Macular input to neurons of the spinoreticulocerebellar pathway

The present report summarizes the results obtained in previous experiments in which the responses to lateral tilt of both reticulocerebellar neurons located in the lateral reticular nucleus (NRL) and ascending spinoreticular tract axons, located in the lateral funiculi of the cervical segments C2-C3, had been recorded in precollicular decerebrate cats. Steady changes in unit activity were evoked by 15-20 degrees tilts which lasted as long as the position of the cat was maintained. Most of the units responsive to tilting showed an increase in discharge rate during tilt in one direction and a decrease in discharge rate during tilt in the opposite direction. Moreover the magnitude of the unitary responses was clearly related to the degree of tilt. The responses of the NRL neurons to tilt were attributed in part to direct efferent vestibuloreticular projections from the Deiters' nucleus, in part to some indirect influence of the lateral vestibulospinal tract on neurons of the cervical ascending spinoreticular pathway. Since most of these ascending units affected by tilt were influenced by stimulation of both ipsilateral and contralateral forelimb nerves, and some of them also by stimulation of high threshold neck muscle afferents, it was postulated that these neurons projected to the forelimb and the neck region of the cerebellar cortex of the anterior lobe. This corticocerebellar region may therefore integrate from time to time not only the signal input originating from macular receptors but also the somatosensory input which originates from neck receptors as a result of the actual displacement in head position induced by the vestibulospinal reflex.