Re-evaluation of cortical and thalamic responses evoked by stimulation of the cerebellar fastigial nucleus in the cat.

In view of the discrepancies in reports about the cerebral responses induced by stimulation of the cerebellar fastigial nucleus in the cat, attempts were made to re-evaluate the effects of stimulation of the fastigial nucleus in the cerebral cortex and thalamus of cats anesthetized with pentobarbital. Stimulation of the fastigial nucleus elicited responses of low amplitude bilaterally in the medial portion of the precruciate cortex in 7 out of 25 animals studied. The responses were mainly composed of a positive wave which reversed its polarity at a depth between 250 and 500 microns from the cortical surface. Presumable relay cells for the responses were detected in the ventromedial nucleus and the medial area of the ventrolateral nucleus of the thalamus. Thalamic neurones showed a tendency to repetitive spike generation with variable latencies after fastigial stimulation, while conditioning stimuli applied to the midbrain reticular formation apparently counteracted it, enhancing the probability of generation of a single spike at a shorter latency. The effect of pentobarbital anesthesia on the fastigio-thalamic transmission is discussed in relation to the inconstant appearance of cortical responses after fastigial stimulation.