Cortical injury impairs contralateral forelimb immobility during swimming: a simple test for loss of inhibitory motor control.

Most animal models of focal injury to the sensorimotor cortex have been aimed at detecting non-use or impairment of the limbs in specific tasks or during spontaneous exploratory behaviors. However, the inability to hold a limb still can be an equally disabling movement disorder. The present study investigated the loss of control of limb immobility that occurs following damage to the forelimb region of the rat sensorimotor cortex (FL-SMC). When swimming forward in a tank of water, adult rats typically hold both forepaws mostly motionless underneath the chin, using primarily the hindlimbs for stroking movements. Following a unilateral FL-SMC lesion, rats hold only the non-impaired forelimb immobile under the chin, and make 'immature' stroking movements with the impaired forelimb. We have devised a simple means of assessing and quantifying this deficit. While the criterion for most tests of motor recovery involves appropriate movement of an impaired limb, this test depends on adequate inhibition of movement as the norm, and may be a useful way to assess the loss of inhibitory motor control and the efficacy of potential restorative interventions.