The role of cerebral cortex in evoked somatosensory activity in cat cerebellum

Abstract

Gross responses were recorded at various cerebellar loci following forepaw electrical stimulation. In chloralose-anesthetized cats responses are large over posterior culmen and adjacent simplex, somewhat reduced in paramedian lobules bilaterally, and considerably smaller in posterior vermis and cerebellar hemispheres. Although variable, responses are usually positive-negative and appear to contain components indicated by notches or slope changes in the main wave. Following decerebration, responses in culmen and simplex are greatly reduced and simplified; responses elsewhere are abolished. Similar results follow administration of barbiturates, KCl-induced depression of cerebral cortex, ablation of somatosensory cortex, lesions of dorsal column, medial lemniscus or nucleus ventralis posterolateralis. In addition to “direct afferent pathways” from forepaw to cerebellum, activity travels via the dorsal column-medial lemniscal system to somatosensory cortex and thence to cerebellum and provides a “cortical loop pathway” which acts to enhance the spinocerebellar responses, resulting in increase of response amplitude and duration as well as enlargement of the responsive area. The major route from cortex to cerebellum appears to be via the corticopontocerebellar pathway, and the wide distribution of the forepaw response beyond forelimb area in culmen is presumably due to the wider distribution of this pathway.