Fastigial neuronal responses to sinusoidal horizontal rotation

Characteristics of nystagmus produced by reversible lesions of the medial cerebellar nuclei in the alert monkey

Synaptic activity of the medial cerebellar nuclei was reversibly blocked in 6 Cebus monkeys by cooling through a sheath implanted alongside the fastigial nucleus. Such lesions produced in the dark a strong nystagmus (slow phase velocity 100-200 deg/sec). The slow phase of nystagmus was predominantly in the horizontal plane and was towards the side of the lesion (ipsilateral drift). The maximum velocity of drift was independent of eye position and was directly related to the degree of cooling. Vision abolished the nystagmus. If lights were turned on during nystagmus the drift velocity rapidly decreased to zero with an instantaneous and an exponential component. It is suggested that these results emphasize the importance of the medial cerebellum, possibly by way of the fastigial nucleus, in balancing the output of the paired vestibular nuclei.

Vestibular inputs to the fastigial nucleus; evidence of convergence of macular and ampullar inputs

1. Experiments have been undertaken on 11 decerebrate cats to investigate the effects of natural vestibular stimulation on the activity of cerebellar fastigial neurons. 2. From recordings in the rostral portion of the nucleus during sinusoidal lateral (roll) and horizontal (yaw) rotation, distinctive patterns of response were observed. 3. The majority of neurons sensitive to vestibular stimulation showed responses to a single modality of vestibular activation. During lateral tilt some neurones showed positional sensititivy, others gave responses related tothe velocity of movement. Other neurones responded in phase with the velocity of movement in the horizontal plane. 4. Aside from these neuronal responses, others provided indications of a convergence of inputs from different sets of vestibular receptors. In particular, several neurons showed a pattern of response that indicated tht they received inputs from otolith receptors and ampullar receptors of the vertical canal. At low velocities of movement their response was positional but with inreasing velocity the magnitude of the response increased and there was a marked phase shift of the discharge towards head velocity. 5. Neurons responding to horizontal rotation often showed positional responses during lateral tilt. There were also indications of a convergence of ampullar inputs from both vertical and horizontal canals. 6. The neural pathways mediating these resonses are discussed in consideration of previous neuroanatomical and neurophysiological data. We consider it likely that several pathways may act to evoke the patterns of response observed, and a role of the cerebellar cortex is indicated.