Separation vs. Association

A key function of the brain is to first, process the fact that we are encountering different types of stimuli at every moment, and second, process the simultaneous fact that while there are these different types of stimuli, there are also many consistencies that reflect modifications of the same stimulus at a higher level of abstraction.

One way to evaluate what a cortical region may be doing with respect to this separation/association dichotomy may be to determine the number of neurons at the first level relative to the second level.

If the ratio of neurons at the first relative to second level is large, then the function of the second level is probably to associate. This is a many-to-few limitation. So various permutations and combinations at the first level are funneled into the reduced dimensionality of the second level. Therefore, some combinations are subsumed.

If the ratio of neurons from first to second levels is small, then there is the potential for expansion. The problem becomes a few-to-many scenario. The same combination at the first level may elicit several possible outcomes at the second level. There is information expansion.

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Slicing up HM's brain

Watch HM's brain being documented, slice by slice.

Click here for live link. At the time of this posting, they are already at the occipital structures. So they may finish soon. Not sure what will happen to the link or the video once this entire process is done.

HM was a famous epileptic patient who had much of his medial temporal structures removed as a treatment for the epilepsy. The result of this operation rendered HM unable to form new long-term memories. This finding was instrumental in the notion that the medial temporal structures, such as the hippocampus, is important for memory. Since his operation, HM has been heavily studied. HM passed away on the 8 Dec 2008 due to respiratory failure. [More about HM]