Response characteristics of cerebellar dentate and lateral cortex neurons to sinusoidal stimulation of neck and labyrinth receptors

Abstract

The activity of 103 individual neurons in the dentate nucleus and 39 neurons in the laterals cortex of the cerebellum has been recorded in decerebrate cats during selective stimulation of neck, vestibular or combined receptors elicited by appropriate rotations about the longitudinal axis (at 0.026 Hz, 8-15° peak amplitude). A proportion of dentate (47.3%) and corticocerebellar (51.5%) neurons responded with a periodic modulation of their firing rate to sinusoidal rotation of the body while the head remained stationary, thus leading to stimulation fo neck receptors. These unit responses depended mainly upon neck position. A proportion of responsive dentate (52.3%) and corticocerebellar (52.9%) units were excited during side-down rotation of the neck and inhibited during side-up rotation, while the remaining units showed the opposite behavior. Within the range of stimulation used, the neck afferent system was not linear, i.e. the gain (imp/s/deg) and the sensitivity of the response (percentage change of the mean firing rate per degree of displacement), slightly decreased by increasing the amplitude of neck rotation from 3° to 12° at 0.026 Hz; however, no change in the phase angle of unit responses was observed. Positional responses were still observed by changing the frequency of neck rotation from 0.026-0.15 Hz at 8°. Dentate (45.9%) and corticocerebellar (29.6%) neurons showed a periodic modulation of their discharge rate during sinusoidal roll tilt of the whole animal leading to stimulation of labyrinth receptors. These unit responses were usually in phase with the peak displacement, due to stimulation of macular receptors. Most of the responsive dentate (71.8%) and corticocerebellar (87.5%) units were excited during side-down tilt of the animal and inhibited during side-up tilt, while the remaining units showed the opposite behavior. Changes in amplitude of stimulation from 5-15° at 0.026 Hz decreased the gain and sensitivity but did not change the phase angle of the unit responses. Both neck and labyrinth inputs were on the average equally effective on the two populations of recorded units. Of 75 dentate neurons tested, 20 units (i.e. 26.7%) responded to both neck and labyrinth inputs, 17 units (i.e. 22.7%) responded to the neck input only, 15 units (i.e. 20%) to the macular input only, while 23 units (i.e. 30.6%) were unresponsive to either type of stimulation. Units receiving convergence from both types of receptors showed either reciprocal or parallel responses to the two inputs. The response characteristics of dentate neurons to combined neck and labyrinth inputs elicited during head rotation closely corresponded to those predicted by a vectorial summation of the individual responses. Neurons of the lateral cortico-nuclear zone of the cerebellum also received convergent signals from the fore- and hind-limbs. Thus, changes in neck or head position could modify the background discharge of both the fore- and/or hind-limb region of the dentate nucleus and the lateral cortex of the cerebellum. The functional significance of te responses of dentate neurons to neck and labyrinth inputs is considered in relation to the known efferent projections of these nuclear neurons to the cerebral cortex and to the spinal cord.