Modulation of microglia as a potential therapy for Alzheimer’s disease

In an ever-growing, ageing population, neurodegenerative disorders such as Alzheimer’s disease and Parkinson’s disease are becoming more and more prevalent. Years of research have uncovered many key players in the origin and progression of these diseases, though an effective therapy is still much sought after.

Neurodegenerative diseases have many pathologies and causes that are specific to each type. Alzheimer’s disease is characterized by the accumulation of toxic proteins called Amyloid beta and a reduction in the connections between neurons (called synapses) in the brain. One common aspect present in all neurodegenerative diseases is neuroinflammation, an immune response mediated largely by cells in the brain called microglia. Microglia make up 5-20% of brain cells and play a significant role in disease and injury. They help to ‘clean up’ in the brain removing dead cells and debris to keep the brain functioning healthily. When the brain is under stress or experiences injury, the microglia are activated and release pro inflammatory mediators called cytokines, such as IL-6 and TNF-a, as a protective mechanism. In a healthy brain, the release of these molecules produces local inflammation that signals back to the microglia that they are needed to clear and repair the injury. In chronic neuroinflammation, the constant activation of microglia leads to sustained release of toxic cytokines and an excessive, pathogenic inflammation ensues. Such chronic inflammation of the nervous tissue triggered by persistent injury or toxic protein build up in the brain is detrimental and eventually results in the microglia damaging the neurons.

In Alzheimer’s disease, it was believed that microglia were initially activated as a defensive response, to fight against and remove the toxic build up of Amyloid beta. It is now hypothesized that as the microglia become chronically activated, they not only act on toxic proteins but start to indiscriminately destroy synapses in the brain. It is at this point that microglia activation may become a damaging pathogenic response, leading to the exacerbation and development of Alzheimer’s disease. Excessive microglia activity on synapses is likely to play a crucial role in the loss of cognition and memory.

An alternate theory proposes a ‘yin and yang’ role of microglia in Alzheimer’s disease. This suggests early on in disease states, microglia are helpful and are positively recruited to sites of toxic Amyloid Beta build up. However as the disease progresses the microglia become overwhelmed, and signal this through excessive release of toxic pro-inflammatory cytokines. One study using brain scanners describes a ‘twin peak’ of microglia activation in patients suffering from Alzheimer’s Disease – an early protective peak and a later pro-inflammatory peak (Wood, H. 2017).

Aligned with the ‘yin and yang’ theory, microglia can exist in one of two phenotypes; a pro-inflammatory form, associated with neurotoxicity (M1) and an anti-inflammatory form associated with neuroprotection (M2) (Song, G.J. and Suk, K. 2017). M1 phenotypes produce toxic pro-inflammatory mediators such as TNF-a and IL-6, which activate the cells to deal with infection or injury. After an initial first response of the M1 microglia, M2 phenotypes produce anti-inflammatory cytokines such as IL-10, which lead to brain repair. Chronic exposure to the pro-inflammatory toxic amyloid beta plaques maintains the activation of M1 microglia, which eventually contributes to neuron and synapse damage, leading to neuronal degeneration. Identifying the mechanisms that modulate the M1/M2 phenotypes could help uncover how local CNS inflammation can lead to the devastating effects of neuronal degeneration. Additionally, finding ways to control and reduce this chronic microglia activation and inflammation in Alzheimer’s’ disease could have huge therapeutic benefit. Several pharmacological interventions to modulate the microglial phenotypes have been investigated, however all have had limited efficacy when tested in clinical trials. A better understanding of the mechanisms involved in microglia activation and polarization is needed to go forward.

Possible therapeutic interventions

One avenue currently being explored involves a class of drug called Histone Deacetylase inhibitors (HDACi). Histone deacetylase’s are enzymes that remove acetyl groups from lysine amino acids in proteins and are involved in regulating gene expression within our cells. Research has shown HDAC’s are implicated in inflammatory responses (Kannan, V. 2013), interacting with the microglia in our brains. It is clear that inhibitors of HDAC suppress this microglia-activated immune response and push microglia towards the protective M2 phenotype (Waang, G. 2015), but exactly how they do so is not known.

It was assumed HDAC inhibitors achieve this by increasing gene expression within microglia. However recently published research by neuroscientists at the University of Leeds (Wood, I. 2017) has shown that HDAC inhibitors can still inhibit microglia activation even when the synthesis of new proteins is stopped, suggesting that their ability to increase gene expression is not important for their effect in microglia. Studying where in the cell that the HDACs exert their effects is the first step in identifying the important target protein, and will ultimately lead to uncovering the mechanisms by which they work to push microglia towards the M2 phenotype, hence reducing the inflammatory response.

One problem with using HDAC inhibitors as a therapeutic intervention is that they act in a very broad non-specific fashion, affecting many cell processes. Uncovering how HDAC inhibitors work to reduce M1 microglia activation would allow an opportunity to develop more targeted and specific therapeutic interventions for Alzheimer’s disease with reduced potential for deleterious side effects. Chronic neuroinflammation is a common pathology shared with other neurodegenerative disorders, and thus finding ways to control and reduce microglia activation using HDAC inhibitors will not only be crucial in Alzheimer’s disease, but will be beneficial more widely.

Author: Rachel Coneys

Edited by: Molly Campbell

References

Wood, H., 2017. Alzheimer disease: Twin peaks of microglial activation observed in Alzheimer disease. Nat Rev Neurol. 13(3):p129

Wood, I., Grigg, R., and Durham, B., 2017. Inhibition of histone deacetylase 1 or 2 reduces microglia activation through a gene expression independent mechanism. Found online at: http://www.biorxiv.org/content/early/2017/02/10/107649

Song, G.J., and Suk, K., 2017. Pharmacological Modulation of Functional Phenotypes of Microglia in Neurodegenerative Diseases. Front Aging Neurosci. 15;9:p139

Kannan, V., Brouwer, N., Hanisch, U.K., Regen, T., Eggen, B.J., and Boddeke, H.W., 2013. Histone deacetylase inhibitors suppress immune activation in primary mouse microglia. J Neurosci Res. 91(9):p1133-42

Wang, G., Shi, Y., Jiang, X., Leak, R. K., Hu, X., Wu, Y., and Chen, J., 2015. HDAC inhibition prevents white matter injury by modulating microglia/macrophage polarization through the GSK3β/PTEN/Akt axis. Proceedings of the National Academy of Sciences, 112(9), 2853-2853.

 

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Through Your Mind

This week we bring the audience of All That is Neuro something that is a little out of the ordinary for our blog. You may be aware that the 8th-14th of May marked Mental Health Awareness week – where people from all over the world took it upon themselves to help spread awareness of mental health and help fight the stigma. Continuing the pledge to ‘spread the word’, here we feature a post about the work of Chloe Thomas, a final year graphic design student at Nottingham Trent University who utilised her artistic talents to portray the anxious mind in its many different states.

What is the topic of your project, how did you approach it and why? 

Anxiety is something that is really close to my heart. I struggle to express how it is making me feel sometimes and don’t believe that people fully understand it. With the “Through Your Mind” project, I aim to raise awareness of what it feels like to be anxious by creating visual representations of the anxious mind. 

I asked friends and family who suffer from anxiety to draw diagrams of what their brain ‘looks like’ when they are feeling anxious. Using this research, I then recreated their ‘brain drawings’ as 3D sculptures.

Discovering mould-making and casting recently has really inspired my work, so I really loved being able to use what I’ve learned in the studio in my final year of university to make something tactile and visually interesting.”

What are the key features of your designs and how do they relate to anxiety? 

“For this project, I built three brains:

  • One in concrete (to represent the heaviness that an anxious brain can feel).

brain 1.jpeg

  • A pink plaster brain covered in silly string (to communicate the confusion and muddled thoughts that can be felt).

brain 2

  • A black and white layered brain (cast in resin to show the lack of enthusiasm and motivation that anxiety can leave you with).” 

    brain 3.jpeg

What do you hope your project will bring to the general public? 

“I’d love to continue with Through Your Mind by creating a larger collection of brain sculptures to represent more individuals. This would show that anyone can suffer from anxiety in their own individual way – which I think is a really important message to communicate.”

I’d like people to feel able to open up about their anxieties by seeing others who have done so. I’d also like to be rid of the stigma attached to anxiety by helping people to gain some understanding of what it feels like and see the sheer number of people who suffer from anxiety. It’s completely normal and nobody should feel that they can’t speak out about it!” 

 

If you are feeling inspired and want to have a gander at more of Chloe’s work, please take a look at her portfolio: chloethomas.myportfolio.com

 

By Molly Campbell

 

 

 

 

 

 

 

Is S-palmitoylation the next phosphorylation? Research surrounding S-palmitoylation, the reversible post-translational modification, is about to explode thanks to novel detection techniques being utilised – get ahead of the game and find out its importance in neurodevelopment.

S-palmitoylation is the reversible attachment of a fatty acid to the cysteine residue of a target protein1. Between 25 and 40% of eukaryotic cellular proteins are membrane associated, whilst an even higher number of intracellular proteins can undergo modifications to localise them to the phospholipid bilayer and increase association with the membrane2. S-palmitoylation typically occurs as a follow-up to prenylation/myristoylation, which attaches a lipid to the protein to promote transient membrane attachments; S-palmitoylation subsequently inhibits protein dissociation from the membrane, as the palmitoylate group acts as a hydrophobic membrane anchor3. 4.

S-palmitoylation is considered to be especially vital in the central nervous system (CNS) – in fact, over 250 proteins expressed in neurones have been identified as S-palmitoylated proteins, and palmitic acid is the fatty acid in the highest concentration in the brain5,6. Examples of S-palmitoylated proteins or protein subunits in the CNS include α subunits of Na+ and β2a subunits of Ca2+ channels , serotonin 1B and 4A receptors, D1 and D2L dopamine receptors, α7 subunit of nicotinic and γ2 subunits of GABAA receptors, as well as various scaffolding proteins , GTPases, chaperones and myelin- associated proteins5,7. However, one notable S-palmitoylated neuronal protein is postsynaptic density-95, PSD-95.

The S-palmitoylation of the postsynaptic scaffolding protein PSD-95 influences synaptic strength and plasticity, due to its involvement in the regulation of postsynaptic glutamate expression. Furthermore, the dysregulation of PSD-95 S-palmitoylation is implicated in Huntington’s disease, whereby altered glutamate expression contributes to disease pathology.

To find out more on the importance of the S-palmitoylation of PSD-95, check out https://badrilla.com/project-landing. If you can spare a couple of minutes, please also fill out the short survey on the landing page – the results are anonymous and will help a final year dissertation project!

  1. Guan, X. & Fierke, C.A. 2011. Understanding Protein Palmitoylation: Biological Significance and Enzymology. Sci China Chem. [Online] 54(12): pp1888-1897. [Date Accessd: 21st February 2017]. Available from: https://www.ncbi.nlm.nih.gov/pubmed/25419213
  2. Pei, Z., Xiao, Y., Meng, J., Hudmon, A. & Cummins, T. R. 2016. Cardiac sodium channel palitoylation regulates channel availability and myocyte excitability with implications for arrhythmia generation. Nature Communications. [Online]. 7(1): 12035. doi: 10.1038/ncomms12035. [Date Accessed: 21st February 2017]. Available from: https://www.ncbi.nlm.nih.gov/pubmed/27337590
  3. Yeste-Velasco, M., Linder, M.E., & Lu, Y-J. 2015. Protein S-palmitoylation and Cancer. Biochimica et Physica Acta. [Online]. 1856(1): pp107-120. [Date Accessed: 21st February 2017]. Available from: https://www.ncbi.nlm.nih.gov/pubmed/26112306
  4. Greaves J. and Chamberlain L. H. 2011. DHHC palmitoyl transferases: substrate interactions and (patho)physiology. Trend in Biochemical Sciences. [Online]. 36(5):245–253. Date Accessed: 11th February 2017.] Available from: http://www.cell.com/trends/biochemical-sciences/fulltext/S0968-0004(11)00014-4
  5. Hayashi T., Rumbaugh G. and Huganir R. L. 2005. Differential regulation of AMPA receptor subunit trafficking by palmitoylation of two distinct sites. Neuron. [Online]. 47(5):709-23. [Date Accessed: 11th February 2017]. Available from: https://ncbi.nlm.nih.gov/pubmed/16129400
  6. Dalva M. B. 2009. Neuronal activity moves protein palmitoylation into the synapse. Journal of Cell Biology. [Online]. 186(1): 7–9. [Date Accessed: 11th February 2017]. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2712999/
  7. Kang R., Wan J., Arstikaitis P., Takahashi H., Huang K., Bailey A. O., Thompson J. X., Roth A. F., Drisdel R. C., Mastro R., Green W. N., John R. Yates J. R. 3rd, Davis N. G. and El-Husseini A. 2008. Neural Palmitoyl-Proteomics Reveals Dynamic Synaptic Palmitoylation. Nature. [Online]. 456(7224): 904–909. [Date Accessed:11th February 2017]. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2610860/#BX1

 

 

Can your gut give you depression?

Do you get butterflies in your stomach when you get nervous or anxious? Ever wondered why this happens? Turns out your gut could play a larger role in your mood than you thought. In recent years’ scientists have been linking disturbances in gut bacteria to several various conditions; including Parkinson’s disease, allergic reactions and depression (Evernsel and Ceylan, 2015).

Mice that are raised in a completely sterile or “germ-free” environment develop an overactive Hypothalamus-Pituitary-Adrenal (HPA) axis (Sudo et al. 2004). This axis is involved in controlling the release of certain neurotransmitters and hormones, including the stress hormone cortisol. Exposing the gut of these mice to certain bacteria leads to recovery of normal function of the HPA system. It is therefore suggested that the bacteria in the gut – or microbiota – can alter the development of their brains. These mice were also found to have altered neurotransmitters such as noradrenaline and serotonin, known to influence mood.

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Figure 1 Visual demonstration of how the gut bacteria can influence brain activity. Taken from: http://sanjosefuncmed.com/successful-aging-part-8b-gut-connections-organs/

In patients that suffer from major depressive disorder, an altered HPA axis has been observed (Dinan and Cryan, 2013). For example, patients often have higher levels of the stress hormone cortisol. Current antidepressants work by changing the levels of noradrenaline and serotonin in the brain. If you link this with the evidence that the bacteria in the mice gut could alter these neurotransmitters, you can hypothesise that altered gut microbiota in humans could cause depression (Figure 1). Alternatively, altering the gut bacteria could potentially treat depression.

The next step for neuroscientists is to actually prove that altered gut microbiota can cause depression or vice versa (Figure 1). Park et al, 2013 used a mouse model of depression to examine HPA alterations and gut microbiota. The mice that presented with chronic depression-like and anxiety-like behaviours also had an elevated HPA axis (and therefore an elevated stress response), and altered gut flora as well as gut motility. These same effects could be brought about by direct administration of corticotropin-releasing hormone.

A proposed theory is that chronic stress causes increased levels of stress hormones from the HPA axis. This can act on the gut to alter bacterial levels and distribution, altering motility and causing diseases such as Irritable Bowel Syndrome (IBS). This further disturbs gut bacteria that can then feedback to the brain, potentiating the stress-response, leading to a cycling that could result in depression. These gut disturbances could explain why patients with IBS also often suffer from depression (Park et al, 2013). The feedback from the gut to the brain is proposed to be brought about by the immune system through activation of inflammatory chemicals that can travel in the blood to act on the brain (Dinan and Cryan, 2013; Figure 1).

Whilst it is easy to get excited about a new possible, effective treatment for depression (something we are sorely lacking), we must bear in mind that these links between gut microbiota and depression have only been shown in preclinical animal models, and the findings are yet to be replicated in humans. It is also still being examined whether the changes in gut bacteria are a primary cause, or a secondary effect from depression. However, full research may lead to the potential of probiotics being used to treat depression (Dinan and Cryan, 2013).

Author: Rosie Porter

Editor: Molly Campbell

References:

Evrensel, A. and Cevlan, M.E. (2015) The Gut-Brain Axis: The Missing Link in Depression. Clinical Psychopharmacology and Neuroscience. 13(3): 239-244

Dinan, T.G. and Cryan, J.F. (2013) Melancholic microbes: a link between gut microbiota and depression? Neurogastroenterol. Motil. 25: 713-719

Park, A.J. Collins, J. Blennerhassett, P.A. Ghia, J.E. Verdu, E.F. Bercik, P. and Collins, S.M. (2013) Altered colonic function and microbiota profile in a mouse model of chronic depression. Neurogastroenterol. Motil. 25(9): 733-741

Sudo, N. Chida, Y. Aiba, Y. Sonoda, J. Oyama, N. Yu, X.N. Kubo, C. Koga, Y. (2004) Postnatal microbial colonization programs the hypothalamic-pituitary-adrenal system for stress response in mice. J Physiol. 558(1): 263-275

 

Creativity: Nature or Nurture?

Creativity exists as an amalgamation of innate talent and acquirable skills, making it the subject of an enduring and complex debate; is creativity a result of nature or nurture? And why are some people more creative than others? Over the years, lesion studies have provided considerable insight regarding the relationship between brain structures and artistic abilities. Additionally, the ever-growing documentation (and scrutiny) of savant/autistic individuals has created a quest to understand and explain the neurological basis of these findings.

What is creativity?

Caselli (2009) conspicuously defined creativity as ‘an attempt to bridge the gap between what is and what should be’ using original or imaginative ideas. The complexity of this debate arises due to the fact that individuals can express creativity across a multitude of disciplines and at different points along a continuum. Innovative behaviour is not restricted to humans, however what separates us from the rest of the animal kingdom, is our utilisation of art as a communicative system. With respect to this, artistic creativity can therefore be defined as a conscious and cognitive process involving several key phases: preparation, incubation, illumination (eureka moment) and production (Heilman, 2016).

So what do we know about the brain already…?

The brain’s outer membrane, and the image people most typically envisage when they imagine the brain, is the cerebral cortex (or cerebrum), which is separated into four lobes: parietal, occipital, temporal and frontal. A structure termed the corpus callosum facilitates communication between the left and right hemispheres – structures that we now understand to differ in their specialities. Information concerning the integration and understanding of stimuli, analysis, language and serial movements (e.g. throwing) are functions belonging to the left hemisphere. The right side of the brain deals with anything concerning visual stimuli e.g. processing, memory, imagery, colour discrimination, as well as the integration of information from all brain regions (Lusebrink, 2004). Just beneath the cerebrum lies the limbic system – a collection of structures responsible for a number of functions including motivation, behaviour, long-term memory, olfaction and (of particular concern in this article) emotion. Despite it being an extensive complex, for the purpose of this article it can broken down into the following critical components: (1) the thalamus – a relay station for all sensory processes occurring in the brain, (2) the hippocampus – crucial in the formation (but not storage) of long-term memories, (3) amygdala – emotional integration of both the conscious (left side) and non-conscious (right side) variety, (4) basal ganglia – the planning and execution of movement.

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Figure 1: the visual pathway from the eye to the brain. Taken from http://visiontherapyofvermont.com/blog/?tag=reading

The visual cortex, found in the occipital lobe, (as shown in figure 1) serves as the final destination for visual information (colour, texture, direction and movement) entering the brain before processing begins. Separation of the visual pathway into two distinct streams, originating in the occipital lobe, forms the basis of the ‘two-stream hypothesis’ and is shown in figure 2. It proposes that form, shape and colour information is received and conveyed to the temporal lobe via the ventral stream, leaving the dorsal stream as the pathway responsible for spatial information travelling to the parietal lobe (Lusebrink, 2004). As the complexity of art increases, recruitment of neurons in the frontal cortex (responsible for higher processing) also increases. Neurons that fire together, wire together’ is a phrase denoting the fact that brain stimulation facilitates brain growth e.g. musicians have been found to have a larger auditory cortex than non-musicians (Heilman, 2016). Nonetheless, this certainty is a source of controversy as it further blurs the boundaries between nature and nurture as explanations for creativity.


Nature or nurture?

The theory of natural selection by Charles Darwin proposes sexual selection as a biological underpinning of art; animals use embellishment and behavioural displays to lure potential sexual partners e.g. peacock’s displaying their tail or the colourful plumage of birds. Such behaviours persisted and evolved with the rise of the Homo sapiens e.g. the use of decorative face paint in African tribes (which is akin to the application of make-up by women in contemporary society). This behaviour highlights many desirable characteristics such as intelligence, creativity and physical aptness that reflect the condition of the brain and body in the flaunting individual (Zaidel, 2010).

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Figure 2: the ventral and dorsal visual pathways originating from the occipital lobe. Taken from https://visionhelp.wordpress.com/2012/08/11/the-three-as-autism-aspergers-and-automobiles-part-5-visual-spatial/ventral-dorsal-stream

Additionally, conclusions drawn from experiments by Reader and Laland (2003) revealed that many birds and non human primates exhibit creativity in the form of cunning and deceptive behaviours, e.g. pigeons teaching each other how to reach food in a difficult place/situation or monkeys rinsing the sand off their sweet potatoes before eating them and passing this on to their relatives. There are many more documented examples of animals using creative methods for survival, leading to an explanation of creativity in humans ‘as an extension of the fundamental biological survival functions’ (Zaidel, 2014) – though this can be extended as an explanation for both sexual and survival functions.

Studying the effects of brain damage, disease or abnormalities can shed some insight into the importance played by specific brain structures or regions. Research concerning savants for example, has been used to try and enhance our understanding of anatomical differences underlying their creative abilities. The term ‘savant’ refers to individuals that possess a constrained yet exceptional level of intellect, in an otherwise defective brain. Savant syndrome can be split into a 50:50 ratio between those who suffer autism and those who have acquired the condition as a result of some form of CNS damage (also known as acquired savant syndrome) (Zaidel, 2014). For example, an interesting MRI study by Treffert (2009) reported the absence of the corpus callosum in the brains of savants that were able to simultaneously scan and interpret two different pages of text. This echoes a fascinating finding by researchers at Cornell University, which found a smaller corpus callosum in writers, musicians and artists (Cox, 2013). Since a component of creativity is considered to be a consequence of the brains’ communicative ability (established previously as the primary role of the corpus callosum), these findings do prove somewhat counterintuitive. Whilst a correlation does not always imply cause and effect, it may be worth looking into this further; perhaps the augmentation of creativity in this way requires that the brain and its hemispheres specialise in a different way by sacrificing efficiency or function in other regions. Of course there is a possibility that multiple factors are at play and that genetic codes have a lot more to answer for. Additionally, lesion studies examining pre and post-damage productivity by artists uncovered the resilience of their skills, regardless of the extent or lateralisation of damage. Artists suffering with dementia and other neurodegenerative diseases display a similar level of resilience even into the later stages of their disease, where a diminished motor activity is what finally stops their art production (Zaidel, 2010). Therefore the extent of the evidence discussed, points towards creativity being an intricate process with no single brain region or pathway playing a dominant role.

Art and emotion: what can art therapy tell us?

Emotion affects almost every aspect of cognition: memory, attention, information processing, etc. (Zaidel, 2010), therefore it is conceivable to propose that art, with the ability to evoke the most powerful of emotions, should have the same effect. A compelling argument states that artistic abilities have evolved as a compensational mechanism allowing the retention of communication in the face of adversity (Zaidel, 2014). This is supported with the emergence of art therapy as a method of treatment for many patients suffering with brain trauma or disease. This technique focuses on how visual and somatosensory information reflect emotions, which in turn affect our experiences, behaviour and thoughts. In this way, art therapy can used to improve emotional and cognitive maturity and has been used to repair damaged cortical pathways. Since all forms of art involve motor movement, victims of stroke, Alzheimer’s disease and schizophrenia were exposed to art therapy in an attempt to activate the basal ganglia – a bridge between motor association and the somatosensory cortices – resulting in a reduction of impairment in these pathways.

The science underlying this therapeutic phenomenon is neuroplasticity – pertaining to the brains’ capacity to reorganise itself in response to injury, disease, new situations or changes in the environment. The success of art therapy is a consequence of its dynamic nature; interaction with art media calls on the activation of sensory, motor and cognitive (interpretation, decision-making, forming internal images) systems (Lusebrink, 2004). Whilst promising, this method remains slightly ambiguous and relatively new. Only time can reveal its efficacy, yet for the sake of this debate it does say a lot about the role of nurture.

So…what can we conclude?

Art is a uniquely human construct that allows us to reflect upon reality as we see it; stylised by our own sense of individuality. Creativity, on the other hand, is subject to influence by both nature and nurture. As already outlined, basic neural underpinnings for creativity can be explained as an evolutionary adaptation for reproduction and survival that grew in complexity as brain anatomy developed. Everyone is innately creative and we use it in our everyday life for a multitude of reasons: negotiations in the workplace, daydreaming, cooking, choosing your clothing and decorating your home. To the contrary, artistic creativity relies very heavily on nurture; an individual’s environment can ease or impede ones artistic faculties.

As Picasso once said:

All children are artists. The problem is trying to stay an artist once one grows up’.

Author: Tiffany Quinn

Edited by: Molly Campbell

References:

Cox, B. (2013). Are some people born creative?. The Guardian. [online] Available at: https://www.theguardian.com/science/blog/2013/sep/19/born-creative-study-brain-hemingway [Accessed 5 Feb. 2017].

 

Heilman, K. (2016). Possible Brain Mechanisms of Creativity. Archives of Clinical Neuropsychology, [online] 31(4), pp.285-296. Available at: https://academic.oup.com/acn/article-lookup/doi/10.1093/arclin/acw009 [Accessed 3 Feb. 2017].

 

Lusebrink, V. (2004). Art Therapy and the Brain: An Attempt to Understand the Underlying Processes of Art Expression in Therapy. Art Therapy, [online] 21(3), pp.125-135. Available at: http://0-www.tandfonline.com.wam.leeds.ac.uk/doi/pdf/10.1080/07421656.2004.10129496?needAccess=true) [Accessed 1 Feb. 2017].

 

Roeser, S. (2010). Emotions and risky technologies. 1st ed. Dordrecht: Springer, pp.62-63.

 

Treffert, D. (2009). The savant syndrome: an extraordinary condition. A synopsis: past, present, future. Philosophical Transactions of the Royal Society B: Biological Sciences, [online] 364(1522), pp.1351-1357. Available at: http://rstb.royalsocietypublishing.org/content/364/1522/1351.short [Accessed 1 Feb. 2017].

 

Zaidel, D. (2010). Art and brain: insights from neuropsychology, biology and evolution. Journal of Anatomy, [online] 216(2), pp.177-183. Available at: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2815940/?tool=pmcentrez [Accessed 3 Feb. 2017].

 

Zaidel, D. (2014). Creativity, brain, and art: biological and neurological considerations. Frontiers in Human Neuroscience, [online] 8. Available at: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4041074/ [Accessed 2 Feb. 2017].

ADHD

ADHD

In this blog article I will underline the key pathophysiology surrounding attention deficit hyperactivity disorder: ADHD

Brain pathophysiology

Many of the brain pathophysiological defects of ADHD are linked with that of the prefrontal lobe, an area which plays a large role in cognition. Therefore, it is uncoincidental that the symptoms linked with the disorder include poor concentration, impulsivity and hyperactivity (R.A. Barkley 2003).  With the use of functional neuroimaging techniques such as FMRI and PET scans, we are able to understand differences in the brain function and structure of ADHD patients, the most prominent of which is seen when using structural MRI. Scans have revealed specific areas in subjects with ADHD are smaller than an individual that does not had ADHD. These areas include the prefrontal lobe, caudate, cerebellum and cerebellar vermis (Zang Yu-Feng 2006).  Using a regional homogeneity method to characterise the local synchronisation of spontaneous brain activity in individuals with methylphenidate and those with placebo. It was seen that in those with the placebo the regional homogeneity of activity was decreased in the bilateral dorsolateral prefrontal cortices. Contrastingly regional homogeneity increased in the bilateral sensorimotor and parieto-visual cortices. Furthermore in those with who taken the methylphenidate, the major effect was down regulation in the right parietal cortex. This down regulation was correlated with decreased symptom scores after 8 weeks of acute methylphenidate doses (Li An et al 2012).

Structural connectivity

Diffusion tensor imaging allows for the imaging of axonal connections between brain areas.  The technique relies on the free movement of water molecules where there are no means of restriction. DTI allows for analysis of the white matter tracts of the brain, where it can map the orientation of the axon and the location. From this, we can image and see the specific connection between brain areas (Konrad and Eickhoff 2010).  Decreased fractional anisotropy (FA) in the right supplementary motor area, right anterior limb of internal capsule, right cerebral peduncle, left middle-cerebellar peduncle, and left cerebellum can be seen in children with ADHD. These results were consistent with those seen with MRI.  Fractional anisotropy is most simply the degree of which the water molecule is directionally dependent as a result of cell membranes and myelin sheath, to that which is free moving with Brownian motion. Finding of lower FA in children with ADHD specifically in these areas is intriguing, as the supplementary motor area has a role in planning, initiation, and execution of motor acts. Additionally, the  right frontostriatal circuitry is thought to be important in the development of organisation and planning (Ashtari et al 2004), which could be linked to poor organisational skills displayed. Consequently, they were able to piece to together links between brain regions and behaviour.

In a study exploring the relationship of frontostriatal structure in ADHD children and behaviour, Casey et al (1997) adopted MRI and behavioural tests. A correlation was found between impulse control and volumetric measure of globus pallidus and basal ganglia. Maps of cortical thickness showed ADHD patients to have a thinner cortex in bilateral frontal regions and the right cingulate cortex, in contrast to those without the disorder. There is now substantial evidence amounting to the role of the cerebellar region in ADHD, as the fractional anisotropy of the area is significant in inattention subscale scores (Durston et al 2003).

Genetics

Genetics accounts for 75% of ADHD cases, as shown by data gathered across four genome-wide association scans investigating the disorder’s heritability. Furthermore, this research placed emphasis on the rarer variants of genes associated with ADHD, such as those coding for DRD4 and DRD5 dopamine receptors (Neale et al 2010).   Further genome-wide association scans show limited overlap  apart with the CDH13. Typically, many of the genes involved are involved in dopaminergic signalling. These include DAT, DRD4, DRD5, TAAR1, MAOA, COMT, and DBH. A mutation in the DRD4–7 receptor results in a wide range of behavioural phenotypes, including ADHD symptoms such as split attention (Kebir et al 2009). Furthermore, polymorphisms of this gene show significance in attention sustained performance tasks (Kieling et al 2006) Given the evidence obtained as a result of the study and meta-analysis, is it clear that DRD4 mutations are influential in displaying ”ADHD-like” phenotypes.  Other genes associated with ADHD include SERT, HTR1B, SNAP25, GRIN2A, ADRA2A, TPH2, and BDNF.

Conclusion

In conclusion, ADHD presents as difficulties in maintaining attention and concentration, but also can affect social aspects. Studies to find clear brain pathologies through imaging techniques have highlighted defects the prefrontal lobe and cerebellum and thus these regional defects are said to contribute to the symptomatic phenotype of the disorder.  There is a clear involvement of biogenic amines, specifically dopamine, with current models showing emphasis on the  mesocorticolimbic dopamine pathway and the locus coeruleus-noradrenergic systems. Furthermore, abnormalities may exist in other pathways such as glutamatergic, serotonergic or cholinergic neurotransmission.   Genetic studies have shown the significance of specific gene variants in contributing to the disorder, specifically those linked to the G-protein coupled receptors DRD4 and DRD5.  Genetic   and phenotypic heterogeneity amongst individuals could explain differences between genetic studies.  However, these differences may exist in different pathways but present the same phenotypic behavioural traits. Meta-analyses have produced a more reliable result than gene-wide association scanning alone, however, the association found only accounts for a small proportion of the genetics of ADHD. Approaches in neuroimaging genetics and epigenetic studies are being investigated to aid a clearer picture of the genetic component of this disorder.

Author: Liam Read

Editor: Molly Campbell

AN, L., CAO, X.-H., CAO, Q.-J., SUN, L., YANG, L., ZOU, Q.-H., KATYA, R., ZANG, Y.-F. & WANG, Y.-F. 2013. Methylphenidate Normalizes Resting-State Brain Dysfunction in Boys With Attention Deficit Hyperactivity Disorder. Neuropsychopharmacology, 38, 1287-1295.

ASHTARI, M., KUMRA, S., BHASKAR, S. L., CLARKE, T., THADEN, E., CERVELLIONE, K. L., RHINEWINE, J., KANE, J. M., ADESMAN, A., MILANAIK, R., MAYTAL, J., DIAMOND, A., SZESZKO, P. & ARDEKANI, B. A. 2005. Attention-deficit/hyperactivity disorder: A preliminary diffusion tensor imaging study. Biological Psychiatry, 57, 448-455.

BARKLEY, R. A. 2003. Issues in the diagnosis of attention-deficit/hyperactivity disorder in children. Brain and Development, 25, 77-83.

CASEY, B. J., CASTELLANOS, F. X., GIEDD, J. N., MARSH, W. L., HAMBURGER, S. D., SCHUBERT, A. B., VAUSS, Y. C., VAITUZIS, A. C., DICKSTEIN, D. P., SARFATTI, S. E. & RAPOPORT, J. L. 1997. Implication of Right Frontostriatal Circuitry in Response Inhibition and Attention-Deficit/Hyperactivity Disorder. Journal of the American Academy of Child & Adolescent Psychiatry, 36, 374-383.

KEBIR, O., TABBANE, K., SENGUPTA, S. & JOOBER, R. 2009. Candidate genes and neuropsychological phenotypes in children with ADHD: review of association studies. J Psychiatry Neurosci, 34, 88-101.

KONRAD, K. & EICKHOFF, S. B. 2010. Is the ADHD brain wired differently? A review on structural and functional connectivity in attention deficit hyperactivity disorder. Human Brain Mapping, 31, 904-916.

NEALE, B. M., MEDLAND, S. E., RIPKE, S., ASHERSON, P., FRANKE, B., LESCH, K.-P., FARAONE, S. V., NGUYEN, T. T., SCHÄFER, H., HOLMANS, P., DALY, M., STEINHAUSEN, H.-C., FREITAG, C., REIF, A., RENNER, T. J., ROMANOS, M., ROMANOS, J., WALITZA, S., WARNKE, A., MEYER, J., PALMASON, H., BUITELAAR, J., VASQUEZ, A. A., LAMBREGTS-ROMMELSE, N., GILL, M., ANNEY, R. J. L., LANGELY, K., O’DONOVAN, M., WILLIAMS, N., OWEN, M., THAPAR, A., KENT, L., SERGEANT, J., ROEYERS, H., MICK, E., BIEDERMAN, J., DOYLE, A., SMALLEY, S., LOO, S., HAKONARSON, H., ELIA, J., TODOROV, A., MIRANDA, A., MULAS, F., EBSTEIN, R. P., ROTHENBERGER, A., BANASCHEWSKI, T., OADES, R. D., SONUGA-BARKE, E., MCGOUGH, J., NISENBAUM, L., MIDDLETON, F., HU, X. & NELSON, S. 2010. Meta-Analysis of Genome-Wide Association Studies of Attention-Deficit/Hyperactivity Disorder. Journal of the American Academy of Child & Adolescent Psychiatry, 49, 884-897.

YU-FENG, Z., YONG, H., CHAO-ZHE, Z., QING-JIU, C., MAN-QIU, S., MENG, L., LI-XIA, T., TIAN-ZI, J. & YU-FENG, W. 2007. Altered baseline brain activity in children with ADHD revealed by resting-state functional MRI. Brain and Development, 29, 83-91.

Brain Disorders: Electroconvulsive Therapy vs Transcranial Magnetic Stimulation.

Shock Therapy: A barbaric treatment no longer in use?
Previous treatments of mental illnesses are often now viewed as extreme. Back in the 1800’s the use of primitive treatment to cut away a section of the patient’s skull to release the ‘evil spirits’ from their body was a common treatment of mental disorders. A tranquilizing chair was also often adopted, where the individual would have to place their head inside a box to reduce blood flow to their brain (Griggs, 2014). Yes, this seems outrageous, terrifying and barbaric in today’s society. In modern day medicine however, the use of biomedical treatments such as electroconvulsive therapy (ECT) and transcranial magnetic stimulation (TMS or rTMS) can actually be used to treat mental disorders, and have shown to be particularly successful in treatment-resistant depression. The unusual historical treatments have often led to the common misconception of ECT in that it is invasive and unsafe, however this is no longer viewed as the case.  These two approaches have actually revolutionized the treatment of depression, and now recent research also supports the use of TMS in those with autism and epilepsy, which will be discussed in this essay.

The History of Electroconvulsive Therapy
Italian neurologists Ugo Cerletti and Lucio Bini developed electroconvulsive therapy. Cerletti was an epilepsy specialist who knew that an electric shock across the head would lead to seizures. He thought that induced convulsions could be used to treat schizophrenia, however these convulsions were far too severe. Along with Kalinowski, a German physician, the researchers developed experiments to test brief electric shocks on humans. Around 10 – 20 ECT shocks on alternate days produced improvement in patients with acute-onset schizophrenia. Another side effect, which appeared to be beneficial, was the retrograde amnesia it caused, as it meant that patients did not report bad experiences towards the therapy. In further use, the treatment was found to be highly effective in depression (Sabbatini, 2016). Today ECT is executed under anesthesia, where small electrical currents are passed through the brain to specific areas via electrodes on the patient’s skull. This targeted therapy makes for an improvement on the previously used treatments such as drugs, as the side effects are minimal. The misconceptions associated with ECT were due to its improper use in its early days. It was often used to control psychiatric patients, whilst conscious and mostly without consent. Various media has depicted ECT in this way, such as the movie/novel One Flew Over the Cuckoos Nest – which is not how the treatment is used (Lilienfeld and Arkowitz, 2014).

ECT Success in Depression
ECT is currently one of the most successful therapies for severe depression, and sometimes in bipolar disorder, however less frequently in other mental disorders. In a meta-analysis by Pagnin et al (2004), ECT was shown to be the superior treatment in comparison to placebos, simulated ECT (a procedure were shocks are not given) and antidepressants, including tricyclic antidepressants and monoamine oxidase inhibitors. Tew et al (1999) found that even older patients with more severe depression and cognitive impairment could tolerate the use of ECT as equally as the younger patients with severe major depression, and even showed some improvement in results.

How does ECT work?
This is one thing we are unsure about, there are many theories postulated however the specific mechanisms leading to improvement in depressive disorders are unknown. It is possible that ECT increases the monoamine neurotransmitters, such as dopamine and serotonin, which are thought to be reduced in those with depression. Another theory is that the treatment stimulates the release of hormones from the hypothalamus or pituitary, as the hypothalamic-pituitary-adrenal axis is thought to be disturbed in depression. The treatment is also thought to have an anti-convulsant nature, rising the threshold for seizures and decreasing their duration. The final theory is that the efficacy of the treatment is due to an increase in synaptogenesis and neurogenesis.

Research by Madsen at al (2000) suggests that ECT leads to an increase in neurogenesis. Rats in this study were either given single electroconvulsive seizures, or a series of 10. Bromodeoxyuridine (BrdU) was administered to the rats; this is a marker commonly used to highlight newly born cells – an indicator of neurogenesis. This marker was used in combination with a specific neuronal marker and co-staining could therefore indicate these new cells were specifically neurons. One month following a single electroconvulsive seizure, there was a 3-fold increase in cells stained with BrdU in the dentate gyrus of the rat’s hippocampus (Figure 1), thus supporting the neurogenesis theory of ECT.

1

Figure 1: A single electroconvulsive seizure (ECS) stimulates cell proliferation. Double immunofluoroscence images showing a rat dentate gyrus from (top) a sham-treated animal and (bottom) an ECS treated-animal. Bromodeoxyuridine (BrdU) was injected six times with 12-hour intervals, starting 72 hours after ECS. Animals survived 1 month after the ECS treatment. Red cells are positive for the mitotic marker BrdU, and green cells are positive for the neuronal marker NeuN. Scale bar, 50 μm (Madsen et al 2000).

Transcranial Magnetic Stimulation: An advancement of ECT
TMS is another brain stimulation technique, which uses magnetic field (similar to that used in an MRI). It is non-invasive and unlike ECT the patients do not have to be under anesthesia. The magnetic currents pass through the brain and skull to induce currents in the brain tissue underlying a coil placed on the scalp of the individual. Similarly to ECT, TMS is a targeted therapy leading to fewer side effects than commonly used medications. This technique does have possible use as a therapeutic method, as it has been shown to be successful in depression. At the American psychiatric association’s annual meeting in 2013 they showed that TMS induced improvement in depression, and these results were maintained throughout the 12-month study, suggesting that the effects of TMS are long lasting. More recently however, TMS has been successfully used as a diagnostic tool for many disorders such as depression, epilepsy and autism (Narayana et al 2015). In epilepsy it has been used to determine the changes in the excitability of neurons in the brains of patients, and how this has altered after treatment with anti-epileptic drugs. TMS can then be applied to these epilepsy patients therapeutically as low-frequency TMS can reduce cortical excitability- it is a very promising treatment approach for people with treatment-resistant refractory epilepsy (Narayana et al 2015). Again, similarly to ECT the biology behind why TMS works is not completely understood. 

Autistic Spectrum Disorder – an upcoming use of TMS
Autistic Spectrum disorder has been considered a possible candidate for the therapeutic use of TMS. Autism affects around 700,000 people in the UK alone. It is a disorder that causes an individual to present with deficits in social interaction and communication across multiple contexts (according to DSM-5).  Advances within Neuroscience have allowed us to determine differences in the brains of those with autistic spectrum disorder, one such variation is that people with autism have larger brain sizes – possibly due to larger numbers of neurons. There is thought to be a lack of communication between various regions in the brain, which could explain why those with autism have difficulties integrating different cognitive functions. Although TMS has been used effectively in the treatment of depression, its use in autism is relatively novel and still being studied.

John Elder Robison, an individual with autistic spectrum disorder, was involved in a six-month study where he received weekly TMS treatments. He revealed that this treatment gave him empathy he had never felt before and the ability to perceive music in a way he had never experienced. To read more about John’s experience, his book ‘switched on’ is available, which details his use of TMS treatment and its effects.

Both of these techniques, ECT and TMS have been very successful in the treatment of depression, and particularly TMS as a diagnostic tool and potential therapeutic tool for many other brain disorders. These brain stimulation techniques hold many advantages over more commonly used treatments such as pharmacotherapy and unquestionably over the tranquilizing chair and primitive treatment. These treatments are not dangerous and could possibly change the way we diagnose and treat specific disorders, including autism, which there is currently few treatments for.

Author: Abbie Byford 

Editor: Molly Campbell

 

References

Griggs, R. 2014. Concise introduction to psychology. Worth Pub.

Sabbatini, R. 2016. The History of Shock Therapy in Psychiatry. Cerebromente.org.br. [Online].

Pagnin, D et al. 2004. Efficacy of ECT in Depression: A Meta-Analytic Review. The Journal of ECT. 20(1),pp.13-20.

Lilienfeld, S. and Arkowitz, H. 2014. The Truth about Shock Therapy. [Online].

Tew, J et al. 1999. Acute Efficacy of ECT in the Treatment of Major Depression in the Old-Old. Am J Psychiatry. 156(12),pp.1865–1870.

Madsen, T el al. 2000. Increased neurogenesis in a model of electroconvulsive therapy. Biological Psychiatry. 47(12),pp.1043-1049.

Narayana, S et al. 2015. Clinical Applications of Transcranial Magnetic Stimulation in Pediatric Neurology. Journal of Child Neurology. 30(9),pp.1111-1124.

https://www.autismspeaks.org/what-autism/diagnosis/dsm-5-diagnostic-criteria

http://www.npr.org/sections/health-shots/2016/04/21/475112703/electric-currents-and-an-emotional-awakening-for-one-man-with-autism

 

 

A Neuroscience Insight into Anxiety Disorders.

I read an article recently in a magazine aimed at individuals my age titled ‘Generation Anxiety’, and this sparked a series of thoughts and questions. The mental health charity Mind reported that 1 in 4 individuals in the UK will experience a mental health problem each year. 1 in 4. A quarter. That’s a lot. Of the listed mental health issues, 4.6 in 100 people will experience anxiety related problems this year.

What is anxiety?
Anxiety disorders describe pathological worry that actually stems from our cave man impulses, our ‘fight or flight response’ to put it simply. In the case of anxiety however an individual may not necessarily have a scenario to trigger such response, it occurs without stimuli, or with stimuli that wouldn’t necessarily be considered as dangerous. The DSM 5 (the diagnostic and statistical manual of mental health disorders) divides pathological anxiety into 3 categories: Obsessive compulsive related disorders, trauma and stressor related disorders and anxiety disorders (Calhoon et al). The stimuli differ for these diagnoses, but in all cases the cognitive and behavioral symptoms of anxiety adversely affect normal functioning.

Having read the initial statistics, I was shocked at how many people are actually affected by this condition. Having read the criteria for diagnosis, I was less shocked, because I most definitely can appreciate how easily worry can spiral and affect an individual in a pathological sense. At the end of the day, life can be very worrying; we are faced with stress every day be it through studying, through work, through financial stresses, all the things that make being an adult quite a burden. As a neuroscience student, I then began to question: what is happening in the brains of individuals for which this worry is becoming pathological? In addition to, why, despite the high incidence of individuals suffering, are there relatively few therapeutic targets identified for treatment? I wanted to explore these questions and present to you the answers from a neuroscience perspective.

Firstly, I encountered this statement from a source discussing mindfulness that I really quite liked:

The underlying mechanism of any mental illness is adaptive and present throughout the human population. A mental disorder is not a new and aberrant development of the human mind but an under- or over-representation of a native mechanism’ (Matthew, 2014).

The brain is complex, and with its complexity it poses the possibility of developing new ‘alternate’ circuits, new mechanisms of neurotransmission with far too much, or less, of the signalling molecule required.

When considering this, anxiety is a sum of its parts. So what has neuroscience taught us?

The Amygdala:
If you keep up to date with our blog you may have read a previous article discussing the role of the amygdala in fear responses. The amygdala is regarded as the ‘central hub’ for the circuitry that creates the sense of fear in our brains. Upon presentation of a threat, the lateral nucleus of the amygdala is activated, and through connections to the central nucleus of the amygdala initiates defensive behavioural mechanisms, freezing being the best example. Connections from the lateral amygdala to the basal amygdala to the nucleus accumbens enable defensive actions, such as avoidance, to be regulated. Don’t worry if the terminology baffles you, the schematic diagram (Figure 1) is a visual representation of these circuits.

Picture1.jpg

Figure 1: A schematic of the circuits underlying defensive reactions and actions (LeDoux and Pine, 2016).

In accordance, individuals with lesions to the amygdala (i.e. damage) fail to show bodily reactions to threat. Imaging studies illustrate that in healthy individuals, a posing threat activates the amygdala, but in the case of an anxiety suffer there is exaggerated amygdala activation. In healthy individuals, cortical areas down-regulate the amygdala, however this capacity is destabilised in individuals with anxiety disorders (LeDoux and Pine, 2016).

Furthermore, a really interesting piece of research by Qin et al (2014) adopted structural and functional MRI to investigate the brain structure of young children who had been diagnosed with early childhood anxiety. Even in children as young as 7-9, MRI illustrated an enlarged amygdala volume, specifically the basolateral amygdala. Findings also showed increased connectivity between the amygdala and distributed brain systems implicated in attention and emotion perception. Machine algorithms suggest that the levels of childhood anxiety could be reliably predicted via amygdala morphometry and intrinsic functional connectivity.

The Bed Nucleus of the Stria Terminalis (BNST):
In neuroscience, one of the techniques in research that I find the most fascinating is optogenetics. This is where neuroscientists transfect cells with genes and render them responsive to light – you can physically turn on and turn off a gene through the presentation of a light stimulus. Two very elegant studies, Jennings et al (2013) and Kim et al (2013) have adopted optogenetics to examine the role of the BNST in anxiety disorders.

Jennings et al looked at the role of the ventral BNST (vBNST) in regulating motivated behaviour and generating anxiety. Interestingly, the study showed that learned anxiety associated with specific environments led to an increase in the activity of some vBNST neurons, and a decrease in activity of others – in accordance with the vBNST consisting functionally distinct cell populations. The vBNST cell populations were found to synapse with neurons of the ventral tegmental area (VTA) that is involved in motivated behaviour and also addiction. Cells that were found to be excited by anxiety-inducing environments excited the VTA cell to which they were synaptically linked, and this activity increased anxiety and decreased reward seeking behaviour. Consistent results were found in vBNST neurons that were inhibited by anxiety seeking behaviour, and activating these connections encouraged reward-seeking behaviour and a reduction in anxiety levels. It must be considered however in these findings that the neurons were artificially excited to induce a state of anxiety – findings might differ in natural anxiety states. Nonetheless this research illustrates nicely that the BNST neuronal population, particularly the ventral neurons, are involved in anxiety. It might be the interplay of these neuronal populations that creates a specific level of anxiety.

Kim et al (2013) investigated whether the cells of the two subregions of the dorsal BNST, the oval nucleus and the anterodorsal BNST regulate anxiety. Their research showed that oval nucleus neurons promoted anxiety, whereas inputs from the amygdala activated the anterodorsal BNST and reduced anxiety. The inhibition of the anterodorsal BNST regions therefore enhanced anxiety. In mice models, the anterodorsal BNST neurons were more active when the mouse was in a safe, familiar environment when compared to an anxiety enhancing one.

The proposed mechanisms from this study are illustrated in figure 2.

2.png

Figure 2: A schematic illustrating the collective findings of Kim and Jennings et al (2013) and the proposed mechanisms underlying anxiety based on their research.

Collectively, these findings suggest evidence that in individuals with anxiety, there are physical structural changes to the brain, producing circuitry alterations that act overall to enhance fear.

For some people, particularly anxiety sufferers themselves, such evidence might be quite daunting; the idea that the brain can actually change its circuitry to produce pathology is quite hard to appreciate. For some, it might be reassuring, as it fights the stigma that unfortunately some associate with mental health conditions as being ‘not real’ – if a structural brain change doesn’t convince you then frankly I’m not sure what will. Regardless of which category you fall into, I would like to point you in the direction of neuroscience research that, using animal models, implies that these alterations can actually be corrected, or silenced, using select methods.

For example, a 2013 study investigated exposure therapy, an element of cognitive behavioural therapy (CBT) and its effects on the structure of the mouse brain. The research showed that exposure therapy silenced and stimulated remodelling of the perisomatic inhibitory synapse. This synapse enables one group of neurons to silence another, and the number of these synapses specifically increased around the fear neurons aforementioned in the amygdala. In the study, mice were placed in a box and exposed to a fear-stimulating situation. A control group did not receive the exposure therapy, whereas a comparison group did. In the exposure therapy group, the mice were placed in the box without the fear inducing situation repeatedly, and this led to a decreased response to the fear stimuli (Trouche et al., 2013). This research nicely demonstrates how the physiological changes in the brain present as behavioural changes. The study also suggested potential new drug targets for improving exposure therapy in humans, which has been found to show a varying success rate thus far.

I hope you will appreciate that the scope of research into anxiety and mental health in neuroscience is extremely large, and thus extends far beyond the content of this article. However, what I do hope to have shown you is how neuroscience research can greatly enhance our understanding of the underlying mechanisms that lead to disorders of the brain such as anxiety, and how these mechanisms produce the behaviour and symptoms that present clinically in sufferers.

Author: Molly Campbell

References:

  1. http://www.mind.org.uk/information-support/types-of-mental-health-problems/statistics-and-facts-about-mental-health/how-common-are-mental-health-problems/
  2. Calhoon, G.G. and Tye, K.M. 2015. Resolving the neural circuits of anxiety. Nature Neuroscience. 18(10), pp. 1394–1404.
  3. Matthew (2014) The Neuroscience of anxiety disorders. Available at: http://www.mindfulnessmd.com/2014/08/09/the-neuroscience-of-anxiety-disorders/ (Accessed: 19 January 2017).
  4. LeDoux, J.E. and Pine, D.S. 2016. Using Neuroscience to help understand fear and anxiety: A Two-System framework. American Journal of Psychiatry. 173(11), pp. 1083–1093.
  5. Qin, S., Young, C., Duan, X., Chen, T., Supekar, K. and Menon, V. 2013. Amygdala subregional structure and intrinsic functional connectivity predicts individual differences in anxiety during early childhood. Biological psychiatry. 75(11), pp. 892–900.
  6. Jennings, J., Sparta, Stamatakis, A., Ung, R., Pleil, K., Kash, T. and Stuber, G. 2013. Distinct extended amygdala circuits for divergent motivational states. Nature. 496(7444), pp. 224–8.
  7. Kim, S., Adhikari, A., Lee, S., Marshel, J., Kim, C., Mallory, C., Lo, M., Pak, S., Mattis, J., Lim, B., Malenka, R., Warden, Neve, R., Tye, K. and Deisseroth, K. 2013. Diverging neural pathways assemble a behavioural state from separable features in anxiety. Nature. 496(7444), pp. 219–23.
  8. Trouche, S., Sasaki, J.M., Tu, T. and Reijmers, L.G. 2013. Fear extinction causes target-specific remodeling of perisomatic inhibitory synapses. Neuron. 80(4). pp. 1-22.

Criminal Brains: Intelligence and Criminal Behaviours

I believe that one of the questions asked at least once in everyone’s lifetime is: “why people do what they do? Why in the same conditions/situations do people make completely different decisions?”. One aspect of human behaviour, in particular, is very intriguing from my point of view: why people choose or find themselves engaging in criminal behaviours, and other individuals in similar circumstances don’t? This article doesn’t obviously claim to be a philosophical treatise, although someone of you may find it fascinating – I don’t have the competences for doing so. However, as neuroscience student what I can do is try to identify some of the factors that may contribute to render some brains more propense to develop the criminal outcome decision compared to others.

Correlation between IQ and criminal behaviours

One of the factors that seems to critically influence the tendency to engage in criminal activities is intelligence. A study conducted by Jovanovic D. et al in 2012 on 120 inmates (60 murderers and 60 non-murderer), showed a negative correlation between IQ and criminal activity; that is, the average IQ of the total inmate population resulted to be lower than the general population. Specifically the average intelligence of the inmates investigated was 95.7, placing the cognitive abilities of these individuals in the lower average of normal abilities. Interestingly, the overall intelligence of the homicide group of inmates (97.4) showed to be greater compared to the non homicide group (94.04), suggesting that the individuals convicted for murders seemed to be “smarter” than individuals convicted for other crimes such as robbery, theft and fraud – but still in the lower average compared to general population. It is important to note that the overall score of IQ was given by the combination of two aspects of intelligence: verbal and manipulative-non verbal tasks. The fascinating fact is that while the non-verbal tasks remain mainly unchanged between all inmates and the general population, the component of the test responsible for decreasing the overall IQ score of all inmates was verbal abilities. Another study from Gibson et al conducted in 2001 showed that the interaction between family adversity and below average verbal IQ at the age of seven is a predictive indicator of early onset of offending behaviours. Once again, it appears that the defecting aspect of intelligence in individuals with higher risk of engaging earlier in criminal behaviours is the verbal part. An even more interesting finding from this study is that the children with higher family adversity factors (i.e. more serious situations), had also lower verbal IQs; in constrast, children with lower adversity factor had higher verbal IQs,. These results can be interpreted in many way, but the most intuitive one would be that specific adverse life events can have an important impact on the development of natural abilities.

Can Intelligence development be promoted to ultimately prevent crime?

I am convinced that the results above describe may raise a number of questions…The first of them being: “what is this trait of personality, i.e. intelligence, that seems to be influenced by the environment and life events?”. Well, it is very difficult to define intelligence, and today, a univocal definition of it that is accepted by everyone still does not exist. However, a broad picture of what intelligence is can be given by describing it as ‘the entirety of abilities that allow individuals to understand and develop complex concepts, engage in diverse types of abstract reasoning and consequently adapt efficiently to the external environment’ (Neisser et al 1996). The finding of Gibson’s et al study seems to suggest that these abilities can be enhanced or reduced by external factors, to the point where the result of this interaction can be considered as a predictive indicator of early offending. Other studies also show that socioeconomical status may have an important impact on neurocognitive abilities during development, in particular on language skills (Hackman et al 2010). It is important to underline the fact that in all the studies here described one particular aspect of intelligence, verbal reasoning, seems to be mostly affected by external adverse events and is found to be responsible for lowering the IQ scoring in criminal adults. This finding opens a wide range of considerations, for example that it is plausible that some adverse events in life may interfere more with the development of some aspects of intelligence, for example verbal skills but not with – or at a lesser extent to – others, such as manipulative/non-verbal abilities. Furthermore, it is possible to infere from this that the study of intelligence in correlation to criminal behaviours can also be used as a tool not only to understand the “reasons” of criminal outcomes, but also for reaching a clearer insight of how intelligence works and is developed.

At this point it is important to notice that, although the external environment plays a crucial role in the development of these abilities, it is widely known that the heritability of intelligence (i.e. the amount of trait variation that is due to the individual genetic code) can be up to 50% (Deary et al 2009). Unfortunately, the genes responsible for heritability of normal range intelligence haven’t been found yet, but what if one day we could map these genes? Could this variable, in conjunction with other indicators such as detrimental life events, family adversity and socioeconomical status, help us to one day predict even more precisely which individuals have higher risk of engaging in criminal activities? And prevent those events by supporting those individuals?

In conclusion, I believe that in light of these considerations, it is reasonable to state that a more supporting society in respect to disadvantaged situations could eventually promote intelligence development in children and could ultimately represent a less criminal society. And even if this wasn’t the case…why not give it a try?

Author: Cristina Cabassi

Edited by Molly Campbell

References:

  • Deary J. I., Johnson W., Houlihan L.M., 2009, Genetic foundations of human intelligence, Hum Genet, 126:215–232

 

  • Gibson L.C., Piquero R.A., Tibbets S.G., 2001 The Contribution of Family Adversity and Verbal IQ to Criminal Behavior,I nternational Journal of Offender Therapy and Comparative Criminology, 45(5), 574-592

 

  • Hackman A.D., Martha J. F., Miachael J.M., 2010, Socioeconomic status and the brain: mechanistic insights from human and animal research, Nat Rev Neurosci; 11(9): 651–659.

 

  • Jovanovic D., Novakovic M., Salamadić A., Petrovic , Maric s., 2012, Analysis of the relation between intelligence and criminal behavior, Journal of Health Sciences, Vol 2, N. 3,

 

  • Neisser et al, 1996, Intelligence: Known and Unknowns, American Psychologist, Vol. 5, N. 2, 77-101

 

 

 

 

 

 

 

 

 

 

 

 

Lights, Genetics, Action – what are the uses of optogenetics in the field of neuroscience?

Optogenetics is a useful tool employed in many areas of biomedical research including and not limited to neuroscience. But does it have the potential to be a clinical weapon? Since the emergence of this technique, the field of optics in science has evolved. As technology changes science has to keep up and with audacious and revolutionary tools such as optogenetics, it is clear that this is happening. But how useful is it really?

What is optogenetics?

It is a new and revolutionary technique used in bioscience for clinical and laboratory function. Breaking down the word gives more meaning; opto meaning the use of light and genetics is reference to the genome. The basic principle of optogenetics is the use of specific wavelengths of light to control and alter a neurone’s firing potential, be it inhibitory or excitatory. The tools involved in the technique (opsins) are actually proteins that are naturally found in microbes, which when activated by light transport the appropriate ions (Boyden, 2011).

This may in theory seems uncomplicated at first glance, however when you delve into the complicated physics and chemistry of the idea, it is not so simple. These opsins, as mentioned, are naturally found in microbes – not humans. This is where genetics and bioengineering are consulted. In order for there to be any clinical use of opsins in humans, then there has to be an efficient way to alter a person’s DNA in order for them to express these opsin proteins. This is a major challenge currently inhibiting the use of opsins in patients.

However, opsins can be used in the lab setting as research. Transgenic mice can be genetically engineered to express the opsins in different parts of the body. This allows scientists to research the consequences of switching certain channels on and off, thereby allowing them to learn more about a disease, condition or anatomy.

There are actually three types of channels used in the technique (Fig.1). Firstly, are the Bacteriorhodopsins which were discovered by Oesterhelt and Stoeckenius (1971; 1973) in the 1970s and were found in the Halobacterium salinarum bacterium. As shown in the diagram, when activated by green light, protons are pumped out of the cell. The next opsin was discovered in the 1980’s and when exposed to yellow/orange light, inhibits the neurone by causing an influx of negative chloride anions (Boyden, 2011). The final and most commonly used opsin is channelrhodopsin. This opsin, when activated by blue light is excitatory, and allows the influx of various cations into the cell, causing depolarisation. This was discovered in Chlamydomonas reinhardtii (a type of algae) (Sineshchekov et al, 2002), and was found to initiate and control phototaxis (Boyden, 2011).

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Fig.1: diagrams showing the three opsin channels used in current research and how they work when the appropriate light is used to stimulate. The colour of the channels represent the light waves used to specifically stimulate the channel. Diagram from (Boyden, 2011).

How does optogenetics work?

First of all you need to use bioengineering in order for the opsin to be expressed in the genome. As Fig.2 shows, the gene for the opsin in question is coupled to a promoter region, allowing for the protein to be expressed via DNA transcription and translation.

Once the genetic construct has been made, it is then introduced into a viral vector. The virus takes up the genetically modified construct and is merged into its genome. The virus is then injected locally to the target neurones only, in the rodent. Here the virus takes on its normal biological function and hijacks the DNA machinery in the rodent, causing it to transcribe the opsin gene. A fibre-optic electrode is then implanted into the rodent and once turned on, it stimulates the opsin channel.

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Fig.2: a summary of how optogenetics works, from the bioengineering to the stimulation of the opsin channel. http://optogenetics.weebly.com/why–how.html

To allow for variability as well as co-occurrence of different opsin channels, each channel is only stimulated at a certain wavelength of light or colour of light (Fig.3). As shown, channel rhodopsin (ChR2) is stimulated by blue light, in the range of roughly 470nm, whereas channel halorhodopsin (NphR) is stimulated by yellow light in the range of roughly 590nm.

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Fig.3: a graph showing the activation wavelengths of various opsin channels. ChemistryViews, 2013.

Once stimulated, the opsin channel opens, leading to an influx/efflux of positive or negative ions depending on the channel’s function. Taking channelrhodopsin as an example; the optrode is turned on, allowing light to shine on the channel and causing it to open. When the neurone is at rest at roughly -70mV, there is a larger concentration of cations on the outside of the cell with respect to the inside, creating a biophysical gradient as well as a concentration gradient. These two factors favour an influx into the neurone, leading to cellular depolarisation and the generation of an action potential. The optrode, when turned on, causes the neurone to fire. This, alongside a whole population of neurones, concurrently depolarise leading to signal generation (summarised in Fig.4).

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Fig.4: diagram summarising the molecular events that occur once the opsin channel (channelrhodopsin used as example) has been stimulated by light. The black arrows indicate biochemical and electrophysical gradient and the direction in which the cations flow. The red arrow is used as a reference point on the action potential trace. +/ symbols represent cations and anions respectively.

Uses of optogenetics in the clinical field

A specific reaction occurs depending on the population of neurones, the location and which pathway you want to control. This is particularly useful for researchers as they can study specific neural circuitry and pathways that may be involved in disorders.

Using optogenetics in the treatment of stroke

The selective stimulation of pyramidal neurones in layer V of the primary motor cortex (M1) was shown to induce the repair processes following a stroke in a study conducted by Cheng et al in 2013. Optogenetics was used in the study in order to test whether specific stimulation of a pathway could help stroke-inflicted mice. Not only were the results promising, but you could say groundbreaking. They found that vs non-optogentically-stimulated mice, the stimulated mice performed significantly better in a range of biochemical as well as behavioural tests.

Fig.5 only provides a snapshot to what they found; Fig.5a shows a significant increase in change in CBF (cerebral blood flow) between stimulated and non-stimulated mice. The reason why CBF was measured is because it is a hallmark for repair. When the brain is damaged, an innate reaction called the neurovascular response kicks in and tries to help alleviate the damage. The % change in CBF was used as a function for repair, because a change indicates that this recovery response is occurring.

There are other hallmarks of repair and recovery, which is shown in Fig.5b. There was a significant increase in neutrophic mRNA expression in either the contralesional primary motor cortex (CM1) or the contralesional somatosensory cortex (CS1). The neurotrophins tested all play a part in repair; Brain Derived Neurotrophin Factor (BDNF) is responsible for inducing axonal and dendritic sprouting; Nerve Growth Factor (NGF) controls the growth of nerves and Neurotrophin3 (NTF3) is involved in survival and differentiation of cells.

Finally, Fig.5c shows results from a distance behavioural test. There is a clear significant difference between distance travelled for stimulated and non-stimulated stroke mice, which if the mice can travel further, indicates recovery from the stroke infliction. If these data can be replicated with a better sample, such as increased number of participants or a change in species tested, then this holds a great potential use in stroke patients.

5aA

5b B

5cC

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Fig.5: figures a. and c. taken from Cheng et al’s study, figure b. is a summarised figure of data from the same study. a. = shows the % change in cerebral blood flow (CBF) between stimulated and non-stimulated mice at post-stroke day 15; b. = graph showing the mRNA content of different neurotrophins in stimulated mice in either the contralesional primary motor cortex (CM1) or the contralesional somatosensory cortex (CS1); c. = a behavioural distance test focusing on stimulated and non-stimulated mice.

 

 

Using optogenetics in the treatment of amnesia

A truly fascinating and useful study using optogenetics was conducted by Ryan et al in 2015, in which they used the technique to study engram cells. These cells are believed to play a part in the consolidation of memory and are changed by learning information (storage) and are reactivated once appropriate retrieval conditions are in place (Tonegawa et al, 2015). This theory is used as the basis behind amnesia in this study. The authors wanted to employ optogenetics in order to stimulate these engram cells, in order to retrieve a memory that should be lost due to disruptions in long term potentiation (LTP) protein synthesis by administrating an inhibitor (anisomycin).

As a control, a group of mice were injected with saline, yet were still optogentically altered to respond to pulses of blue light due to ChR2 presence. The mice were habituated with the optoelectrode and after habituation, they were shocked in order to induce contextual fear conditioning (CFC). This is when the mice associate a previously non-harmful situation/environment to a harmful one due to its association with an electrical shock for example. The mice were then habituated again and optogenetic stimulation induced freezing behaviour in both the anisomycin group (ANI) and the saline group (SAL). Mice were then returned to the chamber they had been shocked in, in order to provoke CFC. Freezing behaviour occurred in both groups and the two groups were then injected with either ANI or SAL. 3 days following the injection, the two groups of mice were returned to the CFC chamber, where the SAL group showed significantly more freezing behaviour (P < 0.01) than ANI, suggesting that ANI had disrupted further memory consolidation of the noxious environment. 4 days later, both groups of mice were stimulated in a non-harmful environment and remarkably, both groups showed significant light-induced freezing behaviour (SAL = P < 0.001 and ANI = P < 0.003) (summarised in Fig.6).

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Fig.6: experimental paradigm from Ryan et al’s 2015 study showing the effects of ChR2 activation by optogenetics on contextual fear conditioning freezing behaviour.

This showed the researchers that by specifically stimulating these engram cells with optogenetics can ‘re-form’ a lost memory. This has massive implications in not only amnesia research, but possibly with disorders such as Alzhemier’s disease, where lost memories can maybe be brought back. The implications are immensely promising, however the logistics and practicality of engineering the technique in humans is a big problem.

Using optogenetics in the treatment of Parkinson’s disease

Parkinson’s disease is a disorder that is characterised by movement deficits, particularly the infamous ‘shuffling gate’. The disease is believed to be caused by the destruction of dopaminergic (DA) neurones within the substantia nigra pars compacta (SNc), leading to atypical neuronal activity in the basal ganglia (BG) (Gradinaru et al, 2009). It is specifically the subthalamic nucleus (STN) and globus pallidus pars interna (GPi) where the irregular neuronal activity leads to the abnormalities including difficulties in initiating and executing motor movements (Albin et al, 1989; Alexander and Crutcher, 1990; DeLong, 1990).

The main advantage of using optogenetics is its selectivity of certain neurones. Deep brain stimulation is a technique used in Parkinson’s disease treatment; however its selectivity for neurones is robust and not very accurate, leading to undesirable effects. This is why Gradinaru et al conducted an optogenetics study in 2009 that primarily targeted the STN by stimulating NpHR opsins, which inhibited the excitatory network. The authors studied the effects of optogenetic stimulation of afferent axonal projections that entered the STN.

Depending on the frequency (be it high or low) determined the therapeutic effects of stimulating the STN afferents using optogenetics. Based on rotational behaviour and head position bias tests, high frequency stimulation (HFS) of the afferents showed remarkable effects (Fig.7). The stimulation ameliorated the parkinsonian symptoms immediately, with significantly reduced rotations per minute (decreased rotations is a sign of Parkinson symptom decrease) compared to pre and post optogenetic HFS. LFS also showed the exact opposite effects.

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Fig.7: the effects of High frequency and Low frequency stimulation (HFS and LFS respectively) on rotational behavioural tests. Note that the Pre and Post indicate before and after optogenetic stimulation. *P < 0.05, n = 5; ***P < 0.001, n = 5 based on t-test.

Based on previous research (Li et al, 2007; Degos et al, 2008) the primary motor cortex M1 and the STN connections may underline the malformed circuitry in Parkinson’s disease. This is why the authors then looked at using optogenetics in the M1. They found that by stimulating from the M1 and recording from the STN (Fig.8a) that similar results were found in reference to LFS and HFS on the rats’ behaviour (Fig.8b).

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Fig.8: a = diagram showing the optogenetic stimulation of the M1 with simultaneous recordings taken from the STN; b = rotational beam behavioural tests at different stages of optogenetic stimulation. **P < 0.01, n = 5 based on t-test.

 

This study helped to show that the selective optogenetic stimulation on certain pathways at high frequency stimulation can help ameliorate Parkinson symptoms, more so than deep brain stimulation. Though hard practically, using optogenetics as a substitute for DBS looks to hold more benefits in treating the movement symptoms.

Using optogenetics in the treatment of Alzheimer’s disease

Alzheimer’s disease (AD) is a lethal neurodegenerative disorder that is the leading cause of dementia and is characterised by memory loss and gradual loss of functional and cognitive processing (Roy et al, 2016). As the disease progresses, neural atrophy gets worse leading to the associated symptoms. Post-mortem brains of patients that suffered AD and those that did not show complete disparity in its structure and general appearance (shown in Fig.9).

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Fig.9: pictures A and B are from patients that did not have Alzheimer’s disease and pictures C and D are from patients that did have the disease. The white arrows are present to compare one picture from another. Note that ventricles in picture D are almost non-existent due to the atrophy. Pictures from Soto-Rojas et al, 2015.

The aforementioned study regarding optogenetic stimulation of engram cells in treating amnesia serves as a basis or as previous research to a study conducted in 2016 by Roy et al. This team built on the ideas and theories found by Ryan et al, as they too used optogenetics to stimulate engram cells (in the hippocampus) in order to retrieve lost memories that occur in the early stages of Alzheimer’s disease (AD).

The team used an AD model which included the over-expression of the delta exon version of presenilin 1 (PSEN1) and also had a mutation in the β-amyloid precursor (APP) leading to increased plaque formations. As well as this model, the team successfully rescued memory recall by optogenetic stimulation in two further models; transgenic mice made from mating c-Fos-tTA mice together (which also had the APP/PSEN1 mutation) and the other model used was a commonly used AD model known as MAPT (Roy et al, 2016). They found that stimulating 7-month-old AD mice could induce memory recall.

It is important to note that a reduction in dendritic spine density has been suggested to play a part in the memory decline of AD patients. Furthermore, the authors detected reduced density of the dentate gyrus (DG) engram spines in 7-month old AD mice against the control (Fig.10).

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Fig.10: the pictures show the difference in spinal density between control mice (left) and the 7-month old AD group (right). There is a clear reduction in the number/density of the dendritic spines in the AD group.

The authors also induced long-term potentiation (LTP) by using optogenetics in order to help consolidate a memory and restoring spine density. Fig.11 shows how after optogenetic-induced LTP, the AD mice group that also had 100 Hz showed an increased freezing response relative to normal AD group. This suggests that optogenetics induced the LTP, which helped the mice recall contextual memory.

This study is relatively recent, yet holds many potential useful future projects, as this way of tackling AD is unique and different from the standard way of administering Acetylcholinesterase inhibitors, which are relatively useless.

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Fig.11: outline of natural memory recall test in which rodents were contextually trained to noxious stimulus and

Future for optogenetics: a conclusion

Optogenetics is a brilliant and innovative tool that has clearly shown promise based on the studies mentioned. The exciting prospect of this tool is that it will only get better and more expansive, as over the next few decades it will surely be used in frontline medicine, as well as in research. The brilliance of using optogenetics in order to try and regain a lost memory is second to none, and is surely a step forward in combating Alzheimer’s disease; a problem that is on the rise in the western world due to increased health procedures.

Though it is very useful in the lab doing research on circuitry, it is harder to employ in in vivo subjects, as the practicality of bioengineering is no easy task. This surely is the biggest obstacle facing optogenetics. Once a way has been found e.g. a possible mixture of implantation by surgery or even using lentiviral vectors, then optogenetics will surely be one of the greatest tools in modern medicine.

 

Author: Ryan Gourlay

References

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Alexander, G.E. and Crutcher, M.D. (1990). Functional architecture of basal ganglia circuits: neural substrates of parallel processing. Trends Neurosci, 13, 266-271.

Boyden, E. S. (2011). A history of optogenetics: the development of tools for controlling brain circuits with light. F1000 Biology Reports3, 11.

Cheng, M.Y., Eric, H., Wanga, E.H., Wooson, W.J., Wanga, S., Suna, G., Leed, A.G., Araca, A., Fennoc, L.E., Deisseroth, K. and Stainberg, G.K. (2014). Optogenetic neuronal stimulation promotes functional recovery after stroke. Proceedings of the National Academy of Sciences, 111, 12913-12918.

Degos, B., Deniau, J.M., Le Cam, J., Mailly, P. and Maurice, N. (2008). Evidence for a direct subthalamo-cortical loop circuit in the rat. Eur. J. Neurosci, 27, 2599-2610.

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Li, S., Arbuthnott, G.W., Jutras, M.J. Goldberg, J.A. and Jaeger, D. (2007). Resonant Antidromic Cortical Circuit Activation as a Consequence of High-Frequency Subthalamic Deep-Brain Stimulation. J. Neurophysiol, 98, 3525-3537.

Oesterhel, D., Stoeckenius, W. (1971). Rhodopsin-like protein from the purple membrane of Halobacterium halobium. Nat New Biol, 233, 149–52.

Oesterhelt, D., Stoeckenius, W. (1973). Functions of a new photoreceptor membrane. Proc Natl Acad Sci U S A, 70, 2853–7.

Roy, D.S., Arons A., Mitchell, T.I., Pignatelli, M., Ryan, T.J. and Tonegawa, S. (2016). Memory retrieval by activating engram cells in mouse models of early Alzheimer’s disease. Nature, 531, 508-512.

Ryan, T.J., Roy, D.S., Pignatelli, M., Arons, A. and Tonegawa, S. (2015). Engram cells retain memory under retrograde amnesia. Science, 348, 1007-1013.

Sineshchekov, O.A., Jung, K.H., Spudich, J.L. (2002). Two rhodopsins mediate phototaxis to low- and high-intensity light in Chlamydomonas reinhardtii. Proc Natl Acad Sci U S A, 99, 8689–94.

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Optogenetics procedure picture: Available from: http://optogenetics.weebly.com/why–how.html.

Wavelengths of light picture: Available from: http://www.chemistryviews.org/details/news/1360543/Optogenetics__Revolutionizing_Biochemistry.html