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Best and Worst of Neuroscience and Neurology – November 2015
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Maybe this is just a reflection of the annual funding cycle, but it is common to see a lot of high quality publications towards the end of year. And as the end of 2015 is approaching, choosing the most interesting articles for this review becomes a more challenging task. Here, I’m presenting only few of the studies that are worth talking about. As usual, the choice of article for inclusion mostly reflects my personal opinion about their significance.
This month, scientific community marked the birthdays of two scientists: Charles Scott Sherrington and Edgar Adrian. Both Englishmen are best known for their shared Nobel Prize in Physiology received in 1932. Their research established the function of neurons in sending the messages within the neural system and demonstrated the basic rules governing this phenomenon. The works of Adrian and Sherrington laid foundation of modern experimental neuroscience.
THE BEST
Fitness level correlates with strength of brain connections in elderly
Resting-state functional connectivity in the brain is a measure of brain health, and it tends to deteriorate with age. A new study demonstrates that brain connectivity in older adults correlates well with the level of cardiovascular fitness.
The measure, however, is not dependent on the level of person’s physical activity: this means that even those who are not particularly active physically but managed to remain fit in old age still rate better in the brain health measurements. The findings help to understand how fitness protects against age-related neurodegeneration and dementia.
Sensors for proprioception found
It is often said that people have five senses, but this is not really correct. At least one obvious sense which is not on the classical list is proprioception: this sense tells us where our body parts are relative to each other and space around us. Obviously, this sense is important for our balance and body movements.
Finding the neural circuits related to the sense of proprioception has turned out to be a difficult task, however. An article published this month identifies Piezo2 as a sensor protein that translates stretching of muscles and tendons into the proprioceptive signal. Interestingly, the same protein mediates the sense of touch.
Human brain more responsive to environmental influences compared to other primates
The term plasticity refers to the propensity of brain to be altered by its environment. New research shows that compared to chimpanzees, our closest evolutionary relative, the human brain is shaped to a much larger degree by social and cultural influences and other adaptations to the changing environment. The brain organization of chimpanzee, on the other hand, is highly heritable (i.e. genetically determined) and shows little variability.
It is quite likely that high brain plasticity was one of the major evolutionary advantages of human species allowing successful adaptation to a vast range of environments.
Where happiness happens?
Happiness is rather elusive thing. Even defining it in scientific terms is far from straightforward: different people feel happy for different reasons.
Japanese scientists used MRI scans to try and locate happiness within the brain structure. It turned out that people who score higher on happiness ratings have a larger mass of grey matter in their precuneus. The precuneus is a part of superior parietal lobule between the cerebral hemispheres. Interestingly, some research demonstrates that meditation causes increase of grey matter in this region.
New concussion biomarker predicts cognitive impairment
Although most concussions get resolved relatively quickly, approximately one in five patients suffers cognitive impairments that last for several months or even longer. It is now believed that diffuse axonal injury associated with concussion may cause degradation of more damaged axons. The degradation process causes formation of some byproducts, including protein SNTF.
Researchers demonstrated that the level of SNTF is higher in people who suffer from greater cognitive dysfunction. Thus, SNTF level can be used as a marker of axonal injury and indicator of potential cognitive impairment in patients.
THE WORST
The worst doesn’t really mean the results are that bad – this is more a reflection of getting some data that do not meet expectations or defy the currently hold views. Very useful lessons can be learned from such findings.
Working memory: not as simple as it looks
Working memory is called upon when a piece of information needs to be kept in mind for a short period of time. It was always assumed that underlying process should be rather simple.
Measuring the brain activity during various memorizing tasks revealed that it involves rhythmic activity of hippocampus which alternates between less excited and more excited states twice per second. The absence of this rhythmic pattern was associated with mistakes in memorizing. Even though the processes behind the pattern are not clear, it is obvious that formation of working memory involves rather complex processes.
Long-term memory formation: unexpected player
Investigation of the functions of ghrelin receptors in the brain yielded an unexpected discovery.Ghrelin is a hormone involved in the control of appetite but it is not present in the brain.
It turned out that ghrelin receptors in the brain play a different function altogether: they can bind to the dopamine receptor and alter its functions. This double dopamine-ghrelin receptor complex is responsible for synaptic plasticity, the ability of synapses to grow and expand. Synaptic plasticity is considered as one of the major processes behind the long-term memory formation. Blocking of ghrelin receptors was shown to inhibit the formation of memory in animal models.
Dopamine signaling and learning process
Another interesting insight into the process of learning was made using a unique technique of very rapid measurements of changes in dopamine levels. And again, the findings were quite different from previous assumptions.
Using a model of an investment game, scientists expected that dopamine response would correlate with the expected reward and actual outcome. It turned out to be more complex: dopamine responses reflected the so-called reward-prediction errors. Dopamine pulses were combining information about what might have happened with information about what actually happened during the game. This is a more informed approach to learning, and it is interesting that it can be studied by direct experimental measurements.
Neurological component of obesity
Obesity, as it turns out, is not just a result of poor diet and lack of exercise – there is also a neurological component to it. Researchers exposed two groups of children, one with normal body weight and one with BMI in obese range, to the smell of food while measuring their brain activity with fMRI. In obese children, the smell of food (smell of chocolate in these experiments) activated brain areas associated with impulsivity. These brain areas are also known to be linked with the development of obsessive-compulsive disorder. These areas remained inactive in children with normal body weight during this experiment.
More probing study may reveal further clue to the neurological triggers of obesity.
Bipolar disorder associated with low level of omega-3 fatty acids
Fatty acids are very important for the health of the brain, and their lowered level ash been shown to be linked to some diseases. A new pilot study has shown that the level of omega-3 fatty acids is lower in people with bipolar disorder, even though the dietary intake of these acids by the patients does not differ from healthy controls. It also appears that the severity of symptoms in patients correlated with the omega-3 deficit.
Previous studies, however, indicated that omega-3 supplementation cannot help in alleviating the symptoms of bipolar disorder. It remains to be seen if any diet modifications can help to the patients.
References
Dies-Suarez P et al. (2015). Obese children fMRI brain connections for food odor stimuli. Radiological Society of North America 2015, Accepted Scientific Posters. Press Release.
Gomez-Robles, A., Hopkins, W., Schapiro, S., & Sherwood, C. (2015). Relaxed genetic control of cortical organization in human brains compared with chimpanzees Proceedings of the National Academy of Sciences DOI: 10.1073/pnas.1512646112
Johnson, V., Stewart, W., Weber, M., Cullen, D., Siman, R., & Smith, D. (2015). SNTF immunostaining reveals previously undetected axonal pathology in traumatic brain injury Acta Neuropathologica DOI:10.1007/s00401-015-1506-0
Kern, A., Mavrikaki, M., Ullrich, C., Albarran-Zeckler, R., Brantley, A., & Smith, R. (2015). Hippocampal Dopamine/DRD1 Signaling Dependent on the Ghrelin Receptor Cell, 163 (5), 1176-1190 DOI:10.1016/j.cell.2015.10.062
Kishida, K., Saez, I., Lohrenz, T., Witcher, M., Laxton, A., Tatter, S., White, J., Ellis, T., Phillips, P., & Montague, P. (2015). Subsecond dopamine fluctuations in human striatum encode superposed error signals about actual and counterfactual reward Proceedings of the National Academy of Sciences DOI:10.1073/pnas.1513619112
Leszczy?ski, M., Fell, J., & Axmacher, N. (2015). Rhythmic Working Memory Activation in the Human Hippocampus Cell Reports, 13 (6), 1272-1282 DOI: 10.1016/j.celrep.2015.09.081
Sato, W., Kochiyama, T., Uono, S., Kubota, Y., Sawada, R., Yoshimura, S., & Toichi, M. (2015). The structural neural substrate of subjective happiness Scientific Reports, 5 DOI: 10.1038/srep16891
Saunders, E., Reider, A., Singh, G., Gelenberg, A., & Rapoport, S. (2015). Low unesterified:esterified eicosapentaenoic acid (EPA) plasma concentration ratio is associated with bipolar disorder episodes, and omega-3 plasma concentrations are altered by treatment Bipolar Disorders, 17 (7), 729-742 DOI:10.1111/bdi.12337
Voss, M., Weng, T., Burzynska, A., Wong, C., Cooke, G., Clark, R., Fanning, J., Awick, E., Gothe, N., Olson, E., McAuley, E., & Kramer, A. (2015). Fitness, but not physical activity, is related to functional integrity of brain networks associated with aging NeuroImage DOI: 10.1016/j.neuroimage.2015.10.044
Woo, S., Lukacs, V., de Nooij, J., Zaytseva, D., Criddle, C., Francisco, A., Jessell, T., Wilkinson, K., & Patapoutian, A. (2015). Piezo2 is the principal mechanotransduction channel for proprioceptionNature Neuroscience, 18 (12), 1