The effects of stimulating cutaneous and splanchnic afferents on cerebellar unit discharges.

1. Electrical stimulation of the right splanchnic nerve evoked the discharge of single units in the right cerebellar cortex of the anaesthetized cat. The majority of the units also responded to electrical stimulation of an area of skin on the right side of the anterior abdominal wall. The units were all located in lobules Vb-f (culmen) of the anterior lobe of the cerebellum, lateral to the paravermian vein. 2. The response evoked by a conditioning stimulus (C) to one afferent pathway was followed by a period during which the response of a testing stimulus (T) to another pathway was diminished or absent. Diminished responsiveness was indicated by a reduction in the probability of the unit firing and a prolongation of the mean latency of the test response. 3. The effects of interaction depended on the interval between conditioning and testing stimuli and could be demonstrated with intervals as long as 150 msec. Complete blocking of the test response occurred with C-T intervals between 30 and 40 msec; at intervals shorter than 25 msec the effects were less intense. 4. If the C-T interval was constant, increasing the strength of the conditioning stimulus or decreasing the strength of the testing stimulus produced in each case a more powerful and prolonged inhibitory effect on the test response. 5. When two successive stimuli were applied to the splanchnic nerve, the discharge evoked by the first stimulus was invariably followed by complete block of the response to the second stimulus over a wide range of intervals.