Activation of the visual cortex imaged by 24-channel near-infrared spectroscopy

Abstract

Near-infrared spectroscopy (NIRS) is a noninvasive technique for continuousmonitoring of the amounts of total hemoglobin (total-Hb), oxygenatedhemoglobin, (oxy-Hb) and deoxygenated hemoglobin (deoxy-Hb). Thepurpose of the present study was to demonstrate the utility of NIRSin functional imaging of the human visual cortex. A new NIRS imagingsystem enabled measurements from 24 scalp locations covering a 9cm sq area. Topographic images were obtained from interpolationsof the concentration changes between measurement points. Five healthysubjects between 25 and 49 years of age were investigated. Aftera resting baseline period of 50 s, the subjects were exposed to avisual stimulus for 20 s, followed by a 50 s resting period in adimly lit, sound attenuating room. The visual stimulus was a circular,black and white, alternating checkerboard. In four of five subjectsthe visual cortex was the most activated area during visual stimulation.This is the first reported use of a NIRSimaging system for assessinghemodynamic changes in the human visual cortex. The typical hemodynamicchanges expected were observed; the total-Hb and oxy-Hb increasedjust after the start of stimulation and plateaued after 10 s of thestimulation period.