October 6, 2010

"everything's better in moderation" - neural plasticity can't be the exception to that rule.

My neuroscience and behavior seminar, required for all us lucky (or not-so-lucky) neuroscience majors at Vassar, has been molded around one of the most broad and frankly irritating topics of all time: plasticity. Like, I get it. Plasticity's important. New synapses, changes in dendritic spines, pruning - all clearly vital to a functioning brain. And it's definitely necessary for someone studying neuroscience - or any science for that matter - to understand that the brain is capable of changing, even after the so-called "critical period".

Environmental conditions, both intra- and extra-cellularly, have the potential to impact the structure of synapses in the brain. Behaviors can even be re-delegated to new brain regions after an injury (dependent on age and other factors of course). While this all sounds great, there is no way that neural plasticity is always a positive thing. It doesn't make sense that something that can change relatively often would be beneficial to most organisms. Perhaps one can make the argument that as the average life span of a species increases, it could be more favorable (over a century, a lot of environmental stimuli can change dramatically), but often times, plasticity studies are done on mice and rats, both of which do not have a long life span at all. What would be the advantage of neural plasticity after the critical period in development in a mouse that only lives for a few months? Could it possibly be more advantageous for the mouse to have strengthened synapses and stable dendritic branches throughout its lifetime? Is it possible that an organism undergoing neuronal plasticity is actually being diverted from stimuli it should be paying attention to?

It's week 5 of my neuroscience seminar. I have read 17 articles on how neuronal plasticity occurs at different levels of an individual's biology (chromatin remodeling all the way up to cortical neurons being remodeled), and how a thousand different neuronal processes are altered by synaptic plasticity and dendritic changes. After discussing all 17 articles, never has one student questioned the real benefits of these changes occurring in post-developmental subjects. Admittedly, neither have I. I don't know if I can attribute my own hesitation to challenge my Professor's apparent deep affection for neurogenesis and plasticity to my fellow classmates, but there is no way they're not also feeling this frustration. Nothing in science is ever good all the time. In fact, most of the time, eventually we find out that things we think are  beneficial turn out to have colossal downsides. So when is it too much when it comes to plasticity?

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