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The organization of behavioral repertoire in the motor cortex

Dr. Michael Graziano

Monday, November 09, 2009, 12:00pm - 07:00pm

Princeton University, Department of Neuroscience

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We found that complex movements with apparent behavioral meaning can be evoked by electrically stimulating the motor cortex of monkeys. These movements unfold during a stimulation train that is applied on a behaviorally relevant time scale (0.5 - 1s). For example, stimulation of one site in cortex caused the mouth to open and the hand to shape into a grip posture and move to the mouth. Stimulation of another site caused the arm to reach out in front of the monkey with the hand open as if prepared to grasp. Stimulation of yet another site caused an apparent defensive movement including a squint, a ducking of the head, and a thrusting outward of the hand as if to protect the face. These complex movements wee organized across the cortical surface in map that was consistent from animal to animal. We were able to reproduced this map mathematically by reducing a highly-dimensional model of the typical monkey movement repertoire onto the two-dimensional space of the cortex. The reduction sought to maximize local smoothness, or the similarity of neighboring representations. This mathematical approach was able to explain on a theoretical basis the organization of a large area of cortex comprising about 20% of the macaque cortical mantle. The model accounted for the gross topography of the primary motor cortex, premotor cortex, supplementary motor cortex, frontal eye field, and supplementary eye field, all adjacent areas involved in motor control. The fundamental principle of organization in motor cortex might not be a map of the body, as was traditionally suggested, but might instead be a two-dimensional map of a highly-dimensional behavioral repertoire.

Background Readings:

A list of my publications with links can be found at: http://www.princeton.edu/~graziano/Publication.html

A useful paper to read as background for the talk is: http://www.princeton.edu/~graziano/Ann_Rev_06.pdf

Dr. Michael Graziano