Reorganization of movement representations in primary motor cortex following focal ischemic infarcts in adult squirrel monkeys.

1. Intracortical microstimulation (ICMS) techniques were used to derive detailed maps of distal forelimb movement representations in primary motor cortex (area 4) of adult squirrel monkeys before and a few months after a focal ischemic infarct. 2. Infarcts caused a marked but transient deficit in use of the contralateral hand, as evidenced by increased use of the ipsilateral hand, and reduced performance on a task requiring skilled digit use. 3. Infarcts resulted in a widespread reduction in the areal extent of digit representations adjacent to the lesion, and apparent increases in adjacent proximal representations. 4. We conclude that substantial functional reorganization occurs in primary motor cortex of adult primates following a focal ischemic infarct, but at least in the absence of postinfarct training, the movements formerly represented in the infarcted zone do not reappear in adjacent cortical regions.