DISCHARGE OF IDENTIFIED DEEP CEREBELLAR NUCLEI NEURONS RELATED TO EYEBLINKS IN THE ALERT CAT

The activity of identified cerebellar nuclear neurons was recorded in the alert cat during blinks induced by corneal air puffs, light flashe s and tones. Eyelid response to air puffs consisted of an early (16.5/-2.7 ms) downward movement followed by two to three late downward ste ps. Blinks induced by flashes or tones presented longer latencies (52. 6+/-4.8 and 50.1+/-8.0 ms). Type A neurons (n = 86) increased their sp ike activity in coincidence with the beginning of the blink, regardles s of the stimulus modality. The late eyelid downward responses were ac companied by corresponding increases in the firing rate of the neuron. Type A neurons were activated mostly from the red nucleus (48/86) or the restiform body (24/86). Type B neurons (n = 30) fired a brief burs t of spikes slightly preceding the blink, followed by a noticeable dec rease in their firing rate. As for type A, the discharge response of t ype B neurons was always the same regardless of the sensory modality. These neurons were activated from the red nucleus (18/30), oculomotor complex (6/30) and restiform body (6/30). Although no precise temporal coupling was found between the beginning of the neuronal response and the start of either the stimulus or the motor response, linear regres sion analysis demonstrated significant relationships between mean firi ng rate of type A and B neurons and eyelid position, velocity and/or a cceleration. Deep cerebellar nuclei neurons presented here seem to be directly involved in the execution of reflexively induced blinks follo wing the smaller details of eyelid motor performance. The opposite beh avior of type A and B cells suggests an interplay of reciprocal action s to determine the ongoing displacements of the lid. Finally, the cere bellum seems to influence blinks through a spread action on many brain stem sites and not exclusively on the red nucleus.