Visually Evoked Cerebral Blood Flow Responses

Abstract

Visual stimulation of the occipital cortex results in an increased cerebral blood flow velocity (CBFV) in the posterior cerebral artery, as measured by transcranial Doppler in 10 normal subjects. The increase was greater for visual stimuli with a higher degree of complexity than for stimuli with a lower degree of complexity (movie with 30.1% maximal amplitude, checkerboard with 21%, and diffuse light with 16.3%). Endexpiratory carbon dioxide pressures (PCO2) influenced the visual‐induced changes of CBFV: Hypercapnia induced a reduction of maximal response amplitude from 30% (normocapnia) to 15% (mild hypercapnia) or 8% (severe hypercapnia) as did hypocapnia (19.6%), indicating a nonlinear interaction between the vasomotor effects of PCO2 and physiological activation. Ischemic lesions of the visual cortex studied in 7 patients also strongly reduced the CBFV responses evoked on the affected side, depending on the degree of infarcted tissue.