Responses of cerebellar fastigial neurons to single muscle activation.

In lightly barbiturized cats, the discharges of neurons in the cerebellar fastigial nucleus (CBM) were recorded while single muscles in ipsilateral forelimb were activated by direct stimulation. The aim was to verify whether CBM cells could selectively detect the activity of afferent fibers from a muscle or a joint and to compare the various response characteristics of the rostral and the caudal division of the nucleus, which are known to control a different muscular periphery. Six muscles were routinely tested, two axial, two proximal and two distal ones. A good percentage of neurons in both partitions of the nucleus responded to the muscles tested (53% and 48% in the rostral and caudal part, respectively). In the rostral part of CBM a large proportion of cells (78% of those responsive) were influenced by one or more muscles having either the same function (the extensors or flexors) or acting on the same joint. Many such neurons showed a marked capability to respond to activation of distal muscles and a prevalence of inhibitory responses mainly on contraction of extensor and axial muscles. In the caudal division of the nucleus, 47% of the responsive cells displayed a stereotyped discharge pattern (excitatory or inhibitory) in response to activation of any tested muscle. In contrast to the rostral CBM the incidence of responses to proximal and distal muscles was about equal in the caudal CBM and a majority of neurons had excitatory responses to flexor muscle contraction. The latencies of the excitatory effects ranged from 8 to 53 ms in rostral and 9 up to 69 ms in caudal CBM.(ABSTRACT TRUNCATED AT 250 WORDS)