Biology 202

2006 First Web Paper

On Serendip

What are learning and memory? Tortora and Grabowski define learning as "the ability to acquire new knowledge or skills through instruction or experience. Memory is the process by which that knowledge is retained over time." Our class model of the brain involves boxes within boxes, inputs from sensory neurons, outputs via motor neurons, and an 'I Function' which can create spontaneous output and gives us a sense of self. This model does not, however, offer an explanation for how we learn. How do some inputs become contained within the brain? How can we explain how we are able to retrieve information and produce an output long after an input has been experienced? It seems like learning requires some kind of long lasting change in the brain. Something in the brain must change; something inside the boxes or in the connections between the boxes. How do we account for these brain alterations in our current model of the brain? Our current model is too static to explain learning; it does not account for the dynamic, constant physical fluctuation and alteration of the brain which occur as a result of encoding experience.

One theory about memory altering the brain involves a memory trace called an engram. Engrams are defined as a "physical or biochemical change in the brain (and other neural tissue) in response to external stimuli." (6) As we experience life, our brains are constantly changing to physically record our memories. "The existence of neurologically defined engrams is not significantly disputed, though its exact mechanism and location has been a persistent focus of research for many decades." (6) Brain plasticity is a property of the nervous system that is related to engrams. Plasticity describes the brain's ability to change the organization of the brain in order to adapt to certain circumstances. Unlike the continuous, gradual effect of engrams, brain plasticity deals more with reorganization of the brain during periods of development or after trauma.

According the Vanderbilt Kennedy Center, "understanding the mechanisms of brain plasticity is essential to developing interventions to overcome brain damage." Research on plasticity has been hailed as the pathway towards curing paralysis which is caused by the severing of the spinal cord. Why isn't the brain able to naturally knit the spinal cord back together after it has been severed? If the spinal cord is cut, the nerves do not reconnect, but rather become independent and function separately. Why doesn't the brain reconnect? Is there a reason why the brain doesn't reconnect? If we could harness the brain's property of plasticity, we might be able to cure paralysis, but we do not know the drawbacks. Is there a reason why there is a limit to brain plasticity? The brain naturally mediates the grow of its neural pathways. "Experience determines which connections will be strengthened and which will be pruned; connections that have been activated most frequently are preserved. Neurons must have a purpose to survive." (2) Why do we have this pruning? Can there be too many neural paths? Is it necessary to prune to avoid conflict within the brain?

I propose a new model for thinking about the brain. I understand that models are supposed to be simplified versions of what they represent, but, in order to incorporate engram theory and the property of plasticity, we need to address some problems with our current model of the brain. The first issue concerns the "I function", the identity or consciousness box in the brain. When the "I function" is a closed box inside the brain, it is hard to place it within our model. Some information is an essential part of our identity while other knowledge is less so yet it can all be brought to conscious awareness. I suppose that the fact that we can store knowledge, that our brains have engrams and plasticity, is how the "I function" theory accounts for the multitude of knowledge that our brain contains. Still, I feel that the "I function" should be a more encompassing box.

Another problem with our model of the brain is the fact that our present model is based on square shaped boxes. Why should we have boxes and not any other shape? The boxes have been compared to different nuclei of the brain, but how can we know if these nuclei are truly responsible for our outputs? The box shape is too uniform; the brain is too complex to be made solely of boxes. Also, I do not think that the boxes should have closed edges. Like the membrane of a neuron, I think the brain's boxes have different permeability under certain conditions. These may be bold statements, during one class discussion; we managed to boil down all brain activity to action potentials. Action potentials, and boxes too, are just one piece of the story. Nothing is so simple that it is based out of one thing. There are always more players in each story. Look at action potentials, they can be broken down into ions and membrane permeability and many other complicated features and processes. There is always more information, a further break down of the smallest known pieces. Part of the journey to 'get it less wrong' involves breaking things down more and connecting information together in new ways.

References

1)Course Home Page1) Grobstein, Paul. "Neurobiology and Behavior 2006". http://serendipstudio.org/bb/neuro/neuro06/ (Our class notes)

2)Brain Plasticity: What Is It? Learning and Memory2) Hoiland, Erin. "Brain Plasticity: What Is It? Learning and Memory." http://faculty.washington.edu/chudler/plast.html (A general overview of how Learning and Brain Plasticity are connected)

3)Brain Plasticity3) McCormick, Kat. "Brain Plasticity". http://serendipstudio.org/bb/neuro/neuro03/web1/kmccormick.html (A previous student's webpaper-lots of applications for brain plasticity)

4) Tortora, G. and Grabowski, S. (1996). Principles of Anatomy and Physiology. (8th ed.), New York: HarperCollins College Publishers.

5)Brain Plasticity5) Vanderbilt Kennedy Center for Research on Human Development. "Brain Plasticity". http://kc.vanderbilt.edu/kennedy/research/topics/plasticity.html (Research site connected to Vanderbilt University)

6)ngram (neuropsychology)6) Wikipedia. "Engram (neuropsychology)." http://en.wikipedia.org/wiki/Engram_%28neuropsychology%29 (Online encyclopedia source)

7)Plasticity (brain)7) Wikipedia. "Plasticity (brain)." http://en.wikipedia.org/wiki/Plasticity_%28brain%29 (Online encyclopedia source)


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