Origin of signals conveyed by the ventral spino-cerebellar tract and spino-reticulo-cerebellar pathway.

The "fictitious" scratch reflex was evoked in decerebrate curarized cats by pinna stimulation. Activity of neurons of the ventral spino-cerebellar tract ( VSCT ) from the L4 and L5 segments of the spinal cord as well as of neurons of the spino-reticulo-cerebellar pathway ( SRCP ) from the lateral reticular nucleus of the medulla oblongata was recorded. Cooling and destruction of different parts of the lumbo-sacral enlargement of the spinal cord were performed. Cooling of the L5 or L6 segment abolished the rhythmic activity in the greater part of the spinal hindlimb centre but did not affect the generation of rhythmic oscillations in the remaining (rostral) segments of the lumbo-sacral enlargement. Under these conditions, neither the rhythmic activity of VSCT neurons located rostral to the thermode nor that of SRCP neurons changed. A normal rhythmic activity of SRCP neurons also persisted after destruction of grey matter in the L3 and L4 segments. It can be concluded that activity of these neurons is independent of whichever part of the enlargement generates rhythmic oscillations. From these observations a hypothesis is advanced that the main content of signals conveyed by the VSCT and SRCP to the cerebellum is the information regarding activity of the generator of rhythmic oscillations that is located in the L3-L5 spinal segments.