Interaction between the activity of an epileptic focus and discrete skilled movements in rats

Sixteen male hooded rats were trained to reach into a narrow feeding tube for small food pellets. The paw movements were photoelectrically detected. An epileptic focus established by local application of 1% picrotoxin on the exposed motor cortex increased the frequency of reaching with the ipsilateral paw and impaired reaching with the contralateral paw. Interictal discharge rate of all ipsilateral foci was increased by reaching in the same way as the slow activity (less than 0.5/sec) of contralateral foci. On the other hand, fast activity (greater than 0.5/sec) of contralateral foci was decreased by reaching. Computer analysis of interictal discharge indicence during 512 msec before and after reaching onset showed that the brief facilitation of discharge (50 msec) during the actual movement was often preceded and followed by more prolonged inhibition (200 msec). The inhibition was better expressed in the contralateral hemisphere. The results are interpreted as due to changes of cortical excitability associated with reaching and to interference of the epileptic focus with the cortical elaboration of the skilled movement.