Michelle Kelrikh, mjkelrikh@gmail.com
Wednesday, March 21, 2012
Evidence: Plasticity
Shenk repeats multiple times in his novel that nothing "from eye color to intelligence" (198) is fixed, and everything is influenced by the GxE paradigm. Yet he contradicts himself and states that "there are strict limits to plasticity...every functioning human brain has an intricate and unchanging design, billions of years in the making..." (201). If our brains have an intricate evolved supposedly "unchanging" design, then how does Shenk consolidate that this is not true for other organs and traits such as height, intelligence, etc? How might our brains have evolved over time to account for the GxE paradigm? Use evidence from the book and relate this to the biological themes of structure and function and/or evolution.
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Plasticity was most likely very important to us centuries ago when we still had to hunt and gather for food because of the brain's ability to memorize locations and map out that information into a type of encyclopedic awareness. It can also be an adaptive mechanism that compensates for lost function which can improve someone's chances of surviving and reproducing in terms of evolution. David Shenk said that the brain "has a remarkable capacity for remodeling after environmental chance" (35). In the taxi driver experiment, a correlation between the size of the posterior hippocampi which houses spatial skills, was in direct relation with the taxi driver's years of experience. This shows that even though our brains have an intricate and unchanging design, it's not true for other traits such as intelligence since the taxi driver experiment just showed that people dont have a limit when it comes to learning and potential.
ReplyDeleteAnd in terms of structure and function, plasticity involves growing neurons, which include multiple axons (for sending out information) and dendrites (which take in information) and where they meet are called synaptic contacts and that's how information is passed around. Over time, a process called synaptic pruning occurs and it deletes old and not frequently used connections and stronger ones determined by usage are kept and strengthened more with synaptic contacts. Synapses need a purpose to stay so connections that aren't used much will get deleted. The process of synaptic pruning is related to evolution on a smaller scale since whatever is unnecessary is rid of so that resources and nutrients can be focused on necessary needs. And in that way, "plasticity enables the process of developing and pruning connections, allowing the brain to adapt itself to the environment" (http://faculty.washington.edu/chudler/plast.html)
(mindy shaw, mindyshaw95@yahoo.com)
As Mindy stated, brain plasticity allows the brain to adapt accordingly to its environment. Brain plasticity is the “capacity to become, over time, what we demand of it” (Shenk 36). Before extensive research was done on the brain, it was “believed that significant changes in the anatomy and organization of the brain were limited to early periods of development in both humans and animals” (Weiten 97). After many studies done by biopsychologists, there is growing evidence “that the anatomical structure and functional organization of the brain is more ‘plastic’ or malleable than widely assumed” (Weiten 97). Through many neuroimaging studies, it has been shown that experience can sculpt the features of brain structure. Shenk uses the example of how “experienced taxi drivers had a greatly enlarged posterior hippocampus” (Shenk 35). Another example would be of how “an area in the somatosensory cortex that receives input from the fingers of the left hand is enlarged in string musicians who constantly use the left hand to finger the strings of their instruments” (Weiten 97). This is a small portion of what plasticity allows human brains to do. Another amazing aspect of plasticity is that when there is damage done to incoming sensory pathways or destroyed brain tissue, the brain can undergo a “neural reorganization” (Weiten 97). Empasizing Mindy, Shenk quotes Harvard psychiatrist Leon Eisenberg about how “the cortex has a remarkable capacity for remodeling after environmental change” (Shenk 35). There have been people who have had to get an either an entire hemisphere removed or their corpus callosum removed due to damage or to help reduce the frequency of seizures in those with epilepsy. Even after these people have had chunks of their brain removed, they are able to live and function normally. This is due to brain plasticity. If the surgery is due at a young enough age, human brains can adapt by creating new synaptic connections that allow the remaining brain to “take over” the functions of the section of brain that has been removed. In this sense, the brain can recover functions that may have been lost due to damage. Also, plasticity is “influenced by genetic factors such as mutations in brain-derived neuronal growth” (http://onlinelibrary.wiley.com/doi/10.1002/ddrr.64/abstract).
ReplyDeleteFrom this information, it is difficult for me to understand why Shenk would claim that there are strict limits to plasticity.
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ReplyDeleteThere are some limits, such as when one’s Broca is damaged, then the person is no longer able to talk. Or if the Wernicke’s area is damaged, then the person is no longer able to understand language. But from many studies, time and time again, the brain seems to prevail in remodeling itself when the environment or physical structure of the brain changes. So there appear to be limits, but I do not agree that they are strict ones because of all the evidence that proves how much plasticity can do to keep the brain functioning well. Over time, the brain has accommodated to the GxE equation because then turning on and off of certain genes due to the environment can influence the reorganization of “neuronal networks in response to environmental stimulation” (http://onlinelibrary.wiley.com/doi/10.1002/ddrr.64/abstract). The brain does seem to have an unchanging design when humans are born. Every “normal” brain is compartmentalized and has the same basic structure. It’s the ability to react to experiences and adapt to the environment through plasticity that makes each brain so unique. The brain is divided up into different lobes that are specialized to carry out specific functions. Agreeing with Mindy, the theme of structure and function in the brain is crucial. When a certain lobe or area of the brain is bigger, whatever that area is specialized for, the person has more of it or is better at utilizing that function. This is why a taxi driver’s hippocampus is enlargened. The hippocampus is a major area where memories are made and kept. Having a larger propensity for brain plasticity increases the chance of surviving and reproducing, tying in plasticity with evolution. Over time, the brain has evolved to be able to adapt to its environment based on experiences. Those who’s brains do not have as large of a propensity to adapt have a smaller chance of surviving and reproducing because they do not have the correct “equipment” to be successful in the environment they live in.
(Kalista Noegroho, Kalista.dara@gmail.com)