Neuroscientists at MIT suspect they've found the brain's system for keeping track of what we do and at least one site in the brain that keeps a sort of checklist.
In a paper published in the Aug. 29 issue of Science, Ann M. Graybiel, the Walter A. Rosenblith Professor of Neuroscience at the McGovern Institute at MIT, and research scientist Naotaka Fujii of the Department of Brain and Cognitive Sciences, report that the "checklist" is in the prefrontal cortex of the brain, known for its ability to keep memories ready to use. They recorded neural activity in the prefrontal cortex in monkeys that had been trained to make a simple series of movements. The neurons whose activity they recorded responded faithfully with each movement, but also had an "extra" response when the monkeys finished the entire sequence of movements.
The experiments described in the report point to the extra response as being the checkmark--the brain's way of noting that the behavior has been done.
Having an overactive checklist system could lead to some of the symptoms displayed by people who suffer from damage to the frontal cortex. If the brain thinks actions are done and doesn't have the urge to do them, apathy can result. Such lack of drive can be a major symptom of frontal lobe dysfunction. At the other extreme, if the brain lacks its checkmark system, behavior may get repeated over and over again. Perseverative behaviors are a classic symptom of frontal lobe damage. It is as though the "it's done" signal is missing. Repetitive behaviors and thoughts are also features of obsessive-compulsive disorder and a range of related disorders that affect both children and adults.
This work also suggests that the prefrontal cortex/basal ganglia brain regions from which the researchers recorded help "package" the individual parts of sequential behaviors into larger chunks. The same nerve cells that make the checkmark also accentuate their activity at the beginning of a movement sequence. A defect in this system may underlie some of the symptoms of Parkinson's disease, in which the patient has to think out each part of a sequence--even a simple movement sequence like standing up from a chair.
For more information about research at the McGovern Institute for Brain Research, see http://web.mit.edu/mcgovern.
A version of this article appeared in MIT Tech Talk on September 10, 2003.
