Correlated activity in the spinocerebellum is related to spinal timing generators

Encoding of information by neuronal populations implies a correlation of neural activity across cells. Therefore recent evidence for correlated activity in different parts of the nervous system has been interpreted as a possible mechanism for functional coupling or coordinated information processing. We compared the activity in the mossy fiber projection, the dorsal spinocerebellar tract (DSCT) with the responses of Purkinje cells in the spinocerebellum for evidence of correlated activity. A principal component analysis of post-stimulus spike activity revealed temporal patterns of correlated Purkinje cell activity in all parts of the spinocerebellum evoked by rapid, small amplitude passive joint rotations in anesthetized cats. The same basic temporal patterns were induced in DSCT neurons by joint rotations and also by direct nerve stimulation, showing that the patterning resulted from centrally generated rather than peripheral timing. The evidence implies that spinal timing generators, activated by mechanical stimulation of the ipsilateral hindlimb, transmit temporally correlated activity to the cerebellum via spinocerebellar pathways resulting in a coherent modulation of activity in diverse areas of the cerebellar cortex thereby providing the basis for a functional coupling.