Corticofugal influences on transmission to the dorsal spinocerebellar tract from hindlimb primary afferents

Summary Effects from the cerebral cortex on neurones of the dorsal spinocerebellar tract (DSCT) were examined: I. In group I units (units receiving monosynaptic excitation from group I fibres) repetitive stimulation of the contralateral sensorimotor cortex usually inhibited impulse transmission from the primary afferents. The inhibition had a latency of 10–20 msec and lasted for 82-100 msec or more. Discharges induced by muscle stretch were also inhibited by the cortical stimulation. DSCT units belonging to extensors and flexors were both inhibited from the cortex. In a small percentage of group I units the inhibition was preceded by a shorter-lasting excitation. 2. FRA units (units receiving excitation from cutaneous and/or high threshold muscle afferents) were typically excited by the cortical stimulation. The excitation was often followed by a period of depression of transmission from the periphery. 3. It is suggested from the effective cortical area and experiments with lesions in the medullary pyramid and in the spinal cord that the inhibition in group I units and the excitation of FRA units are both mediated by the corticospinal tract.Experiments were also made to determine the level where the cell body of a given DSCT unit is located, and the results from 56 units are presented.