Responses of purkinje cells of the cerebellar vermis to neck and macular vestibular inputs

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Abstract
The dynamic analysis of the control exerted by neck and macular vestibular receptors on the cerebellar cortex has been investigated in precollicular decerebrate cats submitted to sinusoidal rotation along the longitudinal axis of the animal at the frequency of 0.026 Hz and at peak amplitudes up to 10° for the neck input and 15° for the macular input. Purkinje (P) cells located in the vermal cortex of the cerebellar anterior lobe, particularly in the longitudinal parasagittal zone which projects to the ipsilateral lateral vestibular nucleus (LVN), showed a sinusoidal modulation of the firing rate in response to sinusoidal stimulation of the neck receptors or the vestibular receptors, the phase of the responses being in most units related to the extreme neck or head position. Mossy fiber (MF) and/or climbing fiber (CF) responses of the same or different P-cells to the two inputs were observed. The sensitivity of the MF-response of the P-cells to the neck input, elicited by sinusoidal rotation of the neck and expressed in per cent of the average firing rate per degree of neck rotation, corresponded on the average to 2.71±1.67, S. D. This value was significantly higher than that of the MF-response of the P-cells to the macular input elicited by sinusoidal tilt along the longitudinal axis of the whole animal, which corresponded to 1.71±1.01, S.D. Most of the MF-responses of the P-cells to the neck input were characterized by an excitation during side-down rotation of the neck and by an inhibition during side-up rotation, whereas most of the MF-responses of the P-cells to the macular input showed just the opposite behavior, being inhibited by side-down tilt of the animal and excited by side-up tilt. Units which received a convergent input from both neck and macular receptors and showed an antagonistic pattern of response to the two inputs were tested during rotation of the head alone, in order to excite simultaneously the two kinds of receptors. Due to the higher sensitivity of the neck over the macular response, the magnitude of the combined response tended to be similar to the difference between the individual ones. Moreover, the phase of the resulting response was always modified with respect to that of the response to the neck input alone, and became in some instances related to velocity of neck rotation rather than to neck position. These findings indicate that opposite responses to neck and macular inputs occur at corticocerebellar level. However, a final integration of the two inputs, leading to suppression of the conflicting responses, may occur either at medullary (LVN) or at spinal cord level.