Signalling properties of identified deep cerebellar nuclear neurons related to eye and head movements in the alert cat.

Abstract

1. The spike activity of deep cerebellar nuclear neurons was recorded in the alert cat during spontaneous and during vestibularly and visually induced eye movements. 2. Neurons were classified according to their location in the nuclei, their antidromic activation from projection sites, their sensitivity to eye position and velocity during spontaneous eye movements, and their responses to vestibular and optokinetic stimuli. 3. Type I EPV (eye position and velocity) neurons were located mainly in the posterior part of the fastigial nucleus and activated antidromically almost exclusively from the medial longitudinal fasciculus close to the oculomotor complex. These neurons, reported here for the first time, increased their firing rate during saccades and eye fixations towards the contralateral hemifield. Their position sensitivity to eye fixations in the horizontal plane was 5-3 + 2-6 spikes s' deg1 (mean + S.D.). Eye velocity sensitivity during horizontal saccades was 0-71 + 0-52 spikes s' deg' s'. Variability of their firing rate during a given eye fixation was higher than that shown by abducens motoneurons. 4. Type I EPV neurons increased their firing rate during ipsilateral head rotations at 0 5 Hz with a mean phase lead over eye position of 95x3 + 9.5 deg. They were also activated by contralateral optokinetic stimulation at 30 deg s'. Their sensitivity to eye position and velocity in the horizontal plane during vestibular and optokinetic stimuli yielded values similar to those obtained for spontaneous eye movements. 5. Type II neurons were located in both fastigial and dentate nuclei and were activated antidromically from the restiform body, the medial longitudinal fasciculus close to the oculomotor complex, the red nucleus and the pontine nuclei. Type II neurons were not related to spontaneous eye movements. These neurons increased their firing rate in response to contralateral head rotation and during ipsilateral optokinetic stimulation, and decreased it with the oppositely directed movements. 6. Saccade-related neurons were located mostly in the fastigial and dentate nuclei. Fastigial neurons were activated antidromically from the medial longitudinal fasciculus, while dentate neurons were activated from the red nucleus. These neurons fired a burst of spikes whose duration was significantly related to saccade duration. Dentate neurons responded during omni-directional saccades, while some fastigial neurons fired more actively during contralateral saccades. 7. These three types of neuron represent the output channel for oculomotor signals of the posterior vermis and paravermis. It is proposed that type I EPV neurons correspond to a group of premotor neurons directly involved in oculomotor control. Type II neurons could be responsible for a widespread distribution of vestibular and visual signals related to postural somatic adjustments. Saccade-related neurons are probably involved in the regulation of the duration of eye movements with directional (fastigial neurons) and nondirectional (dentate neurons) speci...

Cerebellar activation during optokinetic stimulation and saccades

“…Three types of neurons were found in both the dentate nucleus and fastigial nucleus, representing the output channel for motor signals of the posterior vermis. 32 Type II neurons modulated their firing rate in response to head rotation (vestibular stimulation) to one side and OKN to the other side, whereas saccade-related dentate neurons responded during omnidirectional saccades. Thus, neurons of the dentate nuclei are involved in the processing of OKN and saccades.…”

Deficits in Saccades and Fixation During Muscimol Inactivation of the Caudal Fastigial Nucleus in the Rhesus Monkey

“…Neurons in the lobules VIc and VII (Helmchen and Büttner 1995;Kase et al 1980;Llinas and Wolfe 1977;Ohtsuka and Noda 1995;Thier et al 2000) and in the cFN (cat: Gruart and Delgado-Garcia 1994;monkey: Fuchs et al 1993;Helmchen et al 1994;Hepp et al 1982;Kleine et al 2003;Ohtsuka and Noda 1991) display saccade-related bursts of activity. Although most of these neurons also show a steady firing rate during intersaccadic intervals Helmchen et al 1994;Kleine et al 2003;Ohtsuka and Noda 1991), the dysmetria observed during muscimol injection in the cFN is interpreted as resulting from the suppression of the saccaderelated bursts.…”

Properties of Cerebellar Fastigial Neurons During Translation, Rotation, and Eye Movements

“…Specifically, the fastigial nucleus (FN), the most medial of the deep cerebellar nuclei, receives both sensory vestibular signals (Kotchabhakdi and Walberg 1978;Noda et al 1990) and cerebellar cortex projections related to motion processing (Wylie et al 1994). Anatomical and physiological studies have separated the fastigial nucleus into rostral and caudal subdivisions, the two being characterized by different afferent and efferent connectivities, as well as neural sensitivities to eye movement and motion stimuli (Buttner et al 1991;Gruart and Delgado-Garcia 1994;Noda et al 1990). Neurons of the caudal FN, known as the fastigial oculomotor region, are under strong inhibitory control from the oculomotor vermis (lobules VI-VII) (Armstrong and Schild 1978;Noda et al 1990) and are modulated during saccadic (Fuchs et al 1993;Helmchen et al 1994) or smooth-pursuit eye movements (Buttner et al 1991;Gardner and Fuchs 1975;Gruart and Delgado-Garcia 1994).…”

“…Pursuit eye-movement neurons in the caudal FN also modulate during suppression of the rotational vestibuloocular reflex (RVOR). The few studies that have characterized pursuitrelated FN neurons only used rotational stimuli (Buttner et al 1991;Gardner and Fuchs 1975;Gruart and Delgado-Garcia 1994). Very little is known at present regarding how caudal FN neurons respond during the translational VOR (TVOR).…”