Pyramidal input to the basal ganglia in the cat.

In cats with mesencephalic decerebration sparing the cerebral peduncles and ablation of sensorimotor cortex, changes in firing of single neurons of caudate nucleus (CD), putamen (PU), globus pallidus (GP) and entopeduncular necleus (EN) were studied following stimulation of the ipsilateral medullary pyramidal tract (MPT). Cells in CD and PU were not extensively influenced by impulses backfired from MPT (14.7% and 18.7%, respectively). Conversely, a larger number of GP cells (28.1%) and especially EN cells (46.9%) exhibited pronounced changes in their firing following MPT stimulation. The MPT-induced effects on CD and PU were either inhibition or excitations, the latter appearing at latencies greater than 11 ms. The responses observed in GP and EN cells were most frequently excitations, some of which appeared with latencies below 5 ms.