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Archive for 10/11/2011

Primitive brain

I have this picture that appeals to me but for which I have never had an evidence. It is not something I believe or even suspect may possibly be true, more an outside chance but interesting.


Think of the brain stem-part of the brain. In some early organism it was all the brain there was and it did everything. It was not that clever but it was in charge of the whole show. Even now if we have a fair amount of the ancient brain alive we can survive in a vegetative state. We can think of that primitive brain having grown its own on-line computer in the form of the mid-brain. Then later, the mid-brain having grown its own on-line computer in the form of the fore-brain. Each layer has deputized a new layer to do some of its functions while keeping some of its control intact.


For example the area that controls whether we are alert or asleep is deep in the brain stem. It causes the thalamus to be either alert or not. The thalamus causes the cortex to be conscious or not.


Science Daily has an item about research of E. Miller of MIT cited below:

Our brains have evolved a fast, reliable way to learn rules such as “stop at red” and “go at green.” Dogma has it that the “big boss” lobes of the cerebral cortex, responsible for daily and long-term decision-making, learn the rules first and then transfer the knowledge to the more primitive, large forebrain region known as the basal ganglia, buried under the cortex.

Although both regions are known to be involved in learning rules that become automatic enough for us to follow without much thought, no one had ever determined each one’s specific role…

Their results suggest that the basal ganglia first identify the rule, and then “train” the prefrontal cortex, which absorbs the lesson more slowly….

Common wisdom suggests that when we learn new things, the prefrontal cortex figures things out first. Then, as our behaviors become familiar and habitual, the more primitive, subcortical basal ganglia take over so that the now-familiar routines can be run off automatically and occupy less of our thoughts.

“What we found was evidence for something very different,” Pasupathy said. “We found that as monkeys learn new, simple rules-associations analogous to ’stop at red, go at green’-the striatum of the basal ganglia shows evidence of learning much sooner and faster than the prefrontal cortex. But, an interesting wrinkle is that the the monkeys’ behavior improved at a slow rate, similar to that of the slower changes in prefrontal cortex.”

This suggests that while the basal ganglia “learn” first, their output forces the prefrontal cortex to change, albeit at a slower rate. The researchers speculate that perhaps the faster learning in the basal ganglia allows us (and our primitive ancestors who lacked a prefrontal cortex) to quickly pick up important information needed for survival. The prefrontal cortex then monitors what the basal ganglia have learned. Its slower, more deliberate learning mechanisms allow it to gather a more judicious “big picture” of what is going on by taking into account more history and thereby exert executive control over behavior.

Pasupathy, A., & Miller, E. (2005). Different time courses of learning-related activity in the prefrontal cortex and striatum Nature, 433 (7028), 873-876 DOI: 10.1038/nature03287