Basal ganglia and cerebellum receive different somatosensory information in rats.

There are two great subcortical circuits that relay sensory information to motor structures in the mammalian brain. One pathway relays via the pontine nuclei and cerebellum, and the other relays by way of the basal ganglia. We studied the cells of origin of these two major pathways from the posteromedial barrel subfield of rats, a distinct region of the somatosensory cortex that contains the sensory representation of the large whiskers. We injected tracer substances into the caudate putamen or the pontine nuclei and charted the location of retrogradely filled cortical cells. In preliminary studies, we used double-labeling techniques to determine whether the cells of origin of these two pathways send axon collaterals to other subcortical targets. Lamina V of the rat posteromedial barrel subfield contains two distinct populations of subcortically projecting neurons, which are organized into distinct sublamina. . Corticopontine cells are located exclusively in sublamina Vb, the deeper of two sublamina revealed by cytochrome oxidase staining. Corticostriate cells are located almost exclusively in the more superficial sublamina Va. Experiments using double-labeling fluorescent tracers demonstrate that about one-quarter of the corticopontine cells send a collateral branch to the superior colliculus. Other studies have shown that cells in Vb are activated at very short latency after vibrissal stimulation; hence, they would seem to be an appropriate relay for the rapid transmission of sensory information to the cerebellum for use in sensory guidance of movement.