DEACTIVATION OF HUMAN VISUAL-CORTEX DURING INVOLUNTARY OCULAR OSCILLATIONS - A PET ACTIVATION STUDY

Prompted by the observation of decreased glucose metabolism in the str iate 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 w ere performed in 12 healthy volunteers using a (H2O)-O-15-bolus techni que after ear canal irrigation, either with ice cold or warm (44 degre es C) water with the subject's eyes closed. In addition to blood flow increases in areas involved in central vestibular processing, statisti cal subtraction analysis revealed a nearly symmetrical, bilateral high ly significant decrease in the occipital cortex covering Brodmann area s 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 l ess 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 involunt ary 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 inadequat e visual input (oscillopsia) during involuntary ocular oscillations.