Impairments in prehension produced by early postnatal sensory motor cortexactivity blockade

Impairments in prehension produced by early postnatal sensory motor cortex activity blockade. J. Neurophysiol. 83: 895-906, 2000. This study examined the effects of blocking neural activity in sensory motor cortex during earl y postnatal development on prehension. We infused muscimol, either unilater ally or bilaterally, into the sensory motor cortex of cats to block activit y continuously between postnatal weeks 3-7. After stopping infusion, we tra ined animals to reach and grasp a cube of meat and tested behavior thereaft er. Animals that had not received muscimol infusion (unilateral saline infu sion; age-matched) reached for the meat accurately with small end-point err ors. They grasped the meat using coordinated digit flexion followed by fore arm supination on 82.7% of trials. Performance using either limb did not di ffer significantly. In animals receiving unilateral muscimol infusion, reac hing and grasping using the limb ipsilateral to the infusion were similar t o controls. The limb contralateral to infusion showed significant increases in systematic and variable reaching end-point errors, often requiring subs equent 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 end-point accuracy as movements were started from a more lateral position, were less effective using the contralateral limb than ipsilateral limb. With bilater al inactivations, the form of reaching acid grasping impairments was identi cal to that produced by unilateral inactivation, but the magnitude of the r eaching impairments was less. We discuss these results in terms of the diff erential effects of unilateral and bilateral inactivation on corticospinal tract development. We also investigated the degree to which these prehensio n impairments after unilateral blockade reflect control by each hemisphere. In animals that had received unilateral blockade between postnatal weeks ( PWs) 3 and 7, we silenced on-going activity (after PW 11) during task perfo rmance using continuous muscimol infusion. We inactivated the right (previo usly active) and then the left (previously silenced) sensory motor cortex. Inactivation of the ipsilateral (right) sensory motor cortex produced a fur ther increase in systematic error and less frequent normal grasping. Reinac tivation of the contralateral (left) cortex produced larger increases in re aching and grasping impairments than those produced by ipsilateral inactiva tion. 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 n ormal development of skilled motor behavior requires activity in sensory mo tor cortex during early postnatal life.