Sensory integration by the dorsal spinocerebellar tract circuitry

Monosynaptic connections from sensory receptors to the dorsal spinocerebellar tract are believed to have a significant role in the transmission of sensory information to the cerebellum. However, predominant polysynaptic connections with highly convergent afferent input suggest a functional organization based on integrated sensory representations. We explored this possibility by examining the responses of dorsal spinocerebellar tract neurons to inputs from muscle receptors. We compared results from two sets of experiments designed to activate receptors in the gastrocnemius-soleus muscles. In one set (135 cells) we stimulated muscle receptors by stretching the isolated muscles and in the other set (194 cells) the muscle receptors were activated by passive foot flexion, which concurrently activated cutaneous and joint receptors as well. Population responses of the spinocerebellar neurons were quite different for the two types of stimuli. Foot flexion elicited long-latency excitatory responses in a majority (53%) of the cells, while muscle stretch elicited a large fraction of early peaking excitatory responses (28%) and inhibitory responses (38%). The long-latency responses to flexion could not be accounted for by specific cutaneous inputs or by possible delayed reflex contractions. We concluded that both types of population response resulted from the muscle stretch and therefore the responses of dorsal spinocerebellar tract cells to these stimuli do not simply reflect the activity in specific classes of sensory receptors.