Impairments In Prehension Produced By Early Postnatal Sensory-Motor Cortex Activity Blockade. John H. Martin, Laura Donarummo and Antony Hacking. Center for Neurobiology and Behavior, Columbia University and the New York State Psychiatric Institute.
APStracts 6:0511N, 1999.
This study examined the effect of blocking neural activity in sensory-motor cortex during early postnatal development on prehension. We infused muscimol, either unilaterally or bilaterally, into the sensory-motor cortex of cats to block activity continuously between postnatal weeks 3-7. After stopping infusion, we trained animals to reach and grasp a cube of meat and tested behavior thereafter. Animals that had not received muscimol infusion (unilateral saline infusion; age-matched) reached for the meat accurately, with small endpoint errors. They grasped the meat using coordinated digit flexion followed by forearm supination on 82.7% of trials. Performance using either limb did not differ significantly. In animals receiving unilateral muscimol infusion, reaching and grasping using the limb ipsilateral to the infusion were similar to controls. The limb contralateral to infusion showed significant increases in systematic and variable reaching endpoint errors, often requiring subsequent corrective movements to contact the meat. Grasping occurred on only 14.8% of trials, replaced on most trials by raking without distal movements. Compensatory adjustments in reach length and angle, to maintain endpoint accuracy as movements were started from a more lateral position, were less effective using the contralateral limb than ipsilateral limb. With bilateral inactivations, the form of reaching and grasping impairments was identical to that produced by unilateral inactivation, but the magnitude of the reaching impairments was less. We discuss these results in terms of the differential effects of unilateral and bilateral inactivation on corticospinal tract development. We also investigated the degree to which these prehension impairments after unilateral blockade reflect control by each hemisphere. In animals that had received unilateral blockade between PWs 3-7, we silenced on-going activity (after PW 11) during task performance using continuous muscimol infusion. We inactivated the right (previously active) and then the left (previously silenced) sensory-motor cortex. Inactivation of the ipsilateral (right) sensory-motor cortex produced a further increase in systematic error and less frequent normal grasping. Re-inactivation of the contralateral (left) cortex produced larger increases in reaching and grasping impairments than those produced by ipsilateral inactivation. This suggests that the impaired limb receives bilateral sensory-motor cortex control, but that control by the contralateral (initially silenced) cortex predominates. Our data are consistent with the hypothesis that the normal development of skilled motor behavior requires activity in sensory-motor cortex during early postnatal life.
Received 15 July 1999; accepted in final form 8 October 1999.
APS Manuscript Number J592-9.
Article publication pending Journal of Neurophysiology.
ISSN 1080-4757 Copyright 1999 The American Physiological Society.
Published in APStracts on 21 December 1999