brain plasticity: faster than thought (Introduction)

by David Turell , Friday, October 30, 2015, 16:40 (3103 days ago) @ David Turell

Neurons control their firing speeds and make changes more quickly than previously realized:-http://www.sciencedaily.com/releases/2015/10/151029190852.htm-"Neurons communicate by passing electrical messages, known as action potentials, between each other. Each neuron has a highly specialized structural region, the axon initial segment (AIS), whose primary role is in the generation and sending of these messages. The AIS can undergo changes in size and location in response to alterations of a neuron's ongoing electrical activity. However, until now, all such 'AIS plasticity' has been exceptionally slow, occurring over a timescale of days. Work by researchers from the MRC Centre for Developmental Neurobiology (MRC CDN), has found that AIS plasticity can happen quickly, influencing the way cells fire action potentials. These results were published in the online edition of the journal Cell Reports.-***-" Using a technique called 'optogenetics', which allows precise control of neuronal activity with light, they discovered that 3 hours after elevating neuronal activity, the AIS of hippocampal neurons in culture was shortened by approximately 25%.-***-" However, to their surprise, after 3 hours of sustained neuronal activation, neurons with shorter AISs were functionally indistinguishable from their unstimulated counterparts. It turned out that a second form of plasticity was also in action at the same time as AIS shortening, involving molecular alterations to the proteins that drive action potential generation -- voltage-gated sodium channels. This sodium channel modulation acted to balance out any neuronal excitability changes caused by AIS shortening.-***-"The results suggest that brain cells can rapidly alter their structure to fine-tune their function. Since a shorter AIS is associated with decreased electrical excitability in neurons, it could represent a form of adaptation, or 'homeostasis': when neuronal activity is too high in a network, for instance during the early development of the brain, cells shorten their AIS, become less excitable, send fewer action potentials, and thereby return the network to normal levels of activity. This could prove to be an important factor in the brain's responses to perturbed activity, allowing ongoing maintenance of appropriate levels of electrical signalling, even when the inputs to a network have been significantly altered, which might happen in diseases such as epilepsy and bipolar disorder.-"'This work adds a bit of data to confirm the 'biology is messy' dictum. We saw shorter AISs and automatically assumed that our experiments would prove that this results in an excitability reduction. It took some intellectual head scratching and extra experiments to figure out that sodium channels were modulated by a separate pathway and actively counteracted the AIS shortening phenotype."-Comment: Neurons can recognize their level of activity and react to it through a series of feedback channels. The brain can self modulate. To evolve to this level of complexity requires planning, by the brain itself or by God.