Role of the caudal fastigial nucleus in saccade generation. I. Neuronal discharge pattern

Abstract

1. The effects of lesions in both human and nonhuman primates have implicated the cerebellum in the control of rapid eye movements, i.e., saccades. To examine the neural substrate of this control, we recorded the discharge patterns of cerebellar output cells in the fastigial nucleus while monkeys tracked a small, jumping spot of light. 2. In the caudal fastigial nucleus, neurons discharged for saccades in one or several directions. All exhibited a burst. Some also exhibited a saccade-related pause in firing either before or after saccades greater than approximately 3-5 degrees. Thirty-seven percent discharged only a burst, 44% also exhibited a pause before bursts in certain directions, and 19% also paused after the saccade-related burst in certain directions. Although many cells discharged steadily during intersaccadic intervals, few exhibited a robust relation between firing rate and eye position. 3. As a measure of directional selectivity, we plotted the burst lead time as a function of saccade direction for saccades of similar (10 degrees) radial amplitudes. Of 20 neurons tested, 17 burst earliest for contralateral saccades and 1 for upward saccades; 2 others showed little dependence on direction. Of 19 additional units tested only in the horizontal direction, 18 burst earlier for contralateral saccades. 4. For contralateral saccades the burst preceded saccades of all sizes by at least 7.7 ms on average. For ipsilateral saccades, the burst preceded small saccades by an average of 10.3 ms. However, as ipsilateral saccade size increased, the burst began later and later relative to saccade onset so that, on average, it always occurred after the onset of 20 degrees saccades but well before the saccade ended. 5. Many fastigial saccade-related units showed increases in the number of spikes with saccade size and in burst duration with saccade duration in one or more directions. For either relation the highest average correlation coefficients ranged from 0.6 to 0.65. In general, the average correlation coefficients and slopes for either relation were slightly larger for contralateral saccades. Pure burst neurons did not display better average correlations than neurons that also paused. For neurons that also paused either before or after saccades, there was a weak tendency for pause duration to increase with the duration of larger saccades. 6. We tested the effect of eye position on unit discharge in 13 cells by requiring the monkey to make 10 degrees ipsilateral and contralateral saccades from a variety of starting positions.(ABSTRACT TRUNCATED AT 400 WORDS)

Tyrosine Hydroxylase- and Dopamine Transporter-Immunoreactive Axons in the Primate Cerebellum Evidence for a Lobular- and Laminar-Specific Dopamine Innervation

“…For example, numerous studies have demonstrated that schizophrenic subjects display abnormalities in smooth pursuit eye movements (Holzman et al 1973;Hutton and Kennard 1998;Levy et al 1994). The fastigial nucleus, the principal target of efferents from the cerebellar vermis (Ito 1984), is activated during pursuit eye movements (Fuchs et al 1993;Vilis and Hore 1981). Thus, the DA innervation of the primate cerebellar vermis described in the present report may reveal a new locus of action for DA in the pathophysiology of schizophrenia.…”

Cortical and cerebellar activation induced by reflexive and voluntary saccades

“…The Purkinje cells of vermis VI and VII project to the caudal part of the fastigial nucleus, which projects to the vestibular nuclei and saccade-related brainstem nuclei (Noda et al 1990). Electrophysiological experiments and clinical studies suggest that the vermis VI and VII are involved in the direction-selective control of saccade metrics and in saccadic adaptation (Kase et al 1980;Suzuki and Keller 1988;Fuchs et al 1993). Disrupting the posterior vermis, especially area VI, VII and paravermis, in humans using transcranial magnetic stimulation also suggest that these areas are related to the execution of visuallyguided saccades (Hashimoto and Ohtsuka 1995).…”

Multiple Reference Frames for Motion in the Primate Cerebellum

“…Anatomical and physiological studies have separated the fastigial nucleus into rostral and caudal subdivisions (Noda et al, 1990;Buttner et al, 1991). Neurons of the caudal fastigial nucleus are modulated during saccadic or smooth pursuit eye movements (Gardner and Fuchs, 1975;Buttner et al, 1991;Fuchs et al, 1993). In contrast, the rostral division is populated by neurons that are modulated by vestibular stimulation but do not show sensitivity to eye movements (Gardner and Fuchs, 1975;Buttner et al, 1991;Siebold et al, 1997).…”