Color, motion and contrast-response functions measured in human cortex using fmri

Purpose. To measure fMRI tuning funclions in identified visual areas within Human cortex ami investigate the re ationahip between neural activity in the human visual cortex and visual appearance. Methods. Multislice fMRI data were acquired ou a 1.5T Signa using a spiral acquisition sequence whose properties were set to obtain BOLD signals, f.etinotopically organized visual areas in human cortex were located by combii.ing the responses to certain stimuli onto a single flattened cortical représentât on. Results. 1) Color tuning to a variety of spatiotemporal targets was measured. In areas VI and V2. color tuning to low spatial frequency targets parallels corresponding behavioral measurements. 2) Activity within the brains of sub ects with localized lesions was measured, a) Structural scans of observer JW reveal no damage, but functional scans in early visual areas show a clear loss of activity that is consistent with the visual field losv b] Observer GY is a hemiaiiope wi ,h damage in left calcannc cortex and sonic residual vision in his right hemifield. We have located several visual areas in the ciamagrd and normal hemispheres, vnd measured motion and rolui respoii&iviu within these areas. 3) Contrast,-response functions were measured to test whether dyslexia it. associated with a déficit in the magnocellular pathway; no differences were found between dyslexic and control groups. Conclusions. Stimulus tuning functions can be measured to obtain information beyond binary statistical classifications (active/not-active). The spatial scale of the fMRI analysis, the signal-to-noise of the method, and t he ability to carry out extended studies of in dividual brains have opened new possibilities for quantitative neurophysiological measurements in human cortex.