PLASTICITY IMPLICATIONS--RECOVERY OF FUNCTION AFTER INJURY TO MOTOR CORTEX

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One of the difficulties associated with evaluating the relationship between cortical damage/reorganization and functional deficit/recovery is the issue of variability in any stroke model. The patient population is heterogeneous with regard to both the amount and location of damaged cortical territory and, accordingly, the severity and type of physical impairment. This is also true in monkey models of stroke where occlusions of the middle cerebral artery at the same point in the brain gives rise to variable functional outcomes as well as variable regions of damage to the brain. Fortunately, we are now able to non-invasively determine the regions of the brain damaged after stroke with magnetic resonance imaging (MRI) techniques in humans and monkeys alike. Additionally, with the advent of the many neuron recording technique, we can use the information gathered from the MRI scans in experimental monkeys to guide placement of recording electrodes adjacent to permanently damaged regions of cortex or into totally healthy regions of cortex. This technique also allows us to examine changes on a daily basis. In Project 3 we propose to use these technologies to follow reorganizational changes correlated with functional recovery at the single unit level of analysis. Our goal is to test specific hypotheses of cortical reorganization by recording from cortical regions that are important for motor control and likely to be involved in compensatory reorganization during recovery of function after occlusion of the middle cerebral artery or after striato-capsullary infarcts. These two types of experimental manipulation are chosen because they mimic the most common types of strokes seen in humans and are the types of stroke studied in human patients in projects 1 & 2. The experiments in project 4 will allow us to begin to unravel the location of cortical region that when damaged give rise to behavioral deficits as well as those implicated in the recovery of behavioral function after stroke. The proposed experiments represent initial efforts to explore the relationship between cortical reorganization and recovery of function in this manner. In the short term, the specific approach will begin to unravel the complex relationships between damaged cortical territories, reorganizing cortical domains, and behavioral performance. In the long term such knowledge show allow for more accurate prognoses and the design of rehabilitative strategies that are optimal for any given pattern for cortical damage.