Brain, Vol 121, Issue 3 429-435, Copyright © 1998 by Oxford University Press
K Ohtsuka and T Enoki
Recent neurophysiological experiments in the monkey have demonstrated that
the flocculus and the posterior vermis, lobules VIc-VII (oculomotor
vermis), are involved in the generation of pursuit eye movements. Whereas
the functions of the flocculus in the control of smooth pursuit have been
intensively investigated, sufficient data are not available for a
profitable discussion of the functions of the oculomotor vermis in the
control of smooth pursuit. We previously indicated that the posterior
vermis can be electrically stimulated by a focal transcranial magnetic
stimulation (TMS) device through the skull in man, and that focal TMS of
the posterior vermis can modulate saccadic eye movements. In this study we
investigated the effects of cerebellar stimulation on smooth pursuit
metrics in man using a focal TMS device. Focal TMS was applied over the
posterior cerebellum in an area approximately 7 mm lateral and caudal to
the inion, where saccadic eye movements are modulated by TMS, during
horizontal smooth pursuit elicited by a step-ramp target with a constant
velocity of 15 degrees/s in four normal subjects. The TMS device was
triggered after the onset of smooth pursuit during the initial acceleration
phase (latency range = 40-80 ms) or the steady-state tracking phase
(latency range = 300-340 ms). We investigated the effect of TMS on the
velocity and acceleration of smooth pursuit. For smooth pursuit directed
ipsilateral to the stimulation side (ipsiversive), focal TMS of the
posterior cerebellum produced abrupt acceleration of pursuit in both
initial acceleration and steady-state tracking phases. On the other hand,
TMS produced abrupt deceleration of contraversive pursuit in both initial
acceleration and steady-state tracking phases. These findings suggest that
the posterior vermis controls smooth pursuit velocity in a
direction-selective manner in both initial acceleration and steady- state
tracking phases.
ARTICLES
Transcranial magnetic stimulation over the posterior cerebellum during smooth pursuit eye movements in man
Department of Ophthalmology, Sapporo Medical University, School of Medicine, Japan.
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