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Prompted by the observation of decreased glucose metabolism in the striate and 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 H2(15)O-bolus technique after ear canal irrigation with ice cold or warm (44 degrees C) water with the subjects 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.

Repeated PET cerebral blood flow measurements using H2(15)O were performed in 13 patients with confirmed Huntington's disease and nine age-matched controls. The activation paradigm consisted of an externally triggered finger opposition task (1.5 Hz) with the dominant hand, the control condition being the auditory input. In the patients with Huntington's disease, impaired activity of the striatum and its frontal motor projection areas (rostral supplementary motor area, anterior cingulate and premotor cortex) could be demonstrated along with enhanced activity mainly in parietal areas during movement. The results suggest that the pathology of Huntington's disease causes impairment of the output part of the basal ganglia-thalamo-cortical motor circuit and may induce a compensatory recruitment of additional accessory motor pathways involving the parietal cortex.

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Summary: In this study the authors used a whole-spectrum near-infrared spectroscopy approach to noninvasively assess changes in hemoglobin oxygenation and cytochrome-c oxidase redox state (Cyt-Ox) in the occipital cortex during visual stimu lation. The system uses a white light source (halogen lamp). The light reflected from the subject's head is spectrally re solved by a spectrograph and dispersed on a cooled charge coupled device camera. The authors showed the following us ing this approach: (1) Changes in cerebral hemoglobin oxygen ation (increase in concentration of oxygenated hemoglobin, decrease in concentration of deoxygenated hemoglobin) in the The energy requirements of brain tissue at rest are almost entirely met by oxidative metabolism of glucose. Cytochrome-c oxidase (Cyt-Ox) is the terminal electron acceptor of the mitochondrial electron transport chain and responsible for more than 90% of the cellular oxygen consumption. The energy generated in this process is used to synthesize ATP. The mechanism and control of the enzyme have been discussed in recent reviews (Coo per, 1990;Brown, 1992).In sections of brain tissue Cyt-Ox activity and concen trations of the enzyme can be measured with different approaches. Such measurements are well established, and Cyt-Ox activity has been shown to be an endogenous metabolic marker of long-term neuronal activity (Wong Riley, 1989).