Deactivation of human visual cortex during involuntary ocular oscillations

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Abstract
Prompted by the observation of decreased glucose metabolism in the striate and the extrastriate visual cortex in a patient with opsoclonus, we studied the influence of involuntary eye movements on visual cortex activity. Repeated measurements of cerebral blood flow (CBF) by PET were performed in 12 healthy volunteers using a H215 O-bolus technique after ear canal irrigation, either with ice cold or warm (44°C) water with the subject's eyes closed. In addition to blood flow increases in areas involved in central vestibular processing, statistical subtraction analysis revealed a nearly symmetrical, bilateral, highly significant decrease in the occipital cortex covering Brodmann areas 17, 18 and 19 after ice water stimulation of either ears. Region of interest analysis revealed in all subjects a mean decrease in regional CBF (rCBF) of 12.8% (range 4.6–21.0%) in these areas. A similar but less pronounced effect (mean rCBF decrease in visual cortex 4.8%, range 1.1–11.5%) was observed after warm water irrigation. The observations suggest that deactivation of the visual cortex is induced by involuntary ocular oscillations. This deactivation is not dependent on changes of the retinal input (eyes closed). The physiological significance of this hitherto unknown phenomenon may be the protection from inadequate visual input (oscillopsia) during involuntary ocular oscillations.

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