A NOVEL NEAR-INFRARED SPECTROPHOTOMETRY SYSTEM USING MICROPROBES - ITS EVALUATION AND APPLICATION FOR MONITORING NEURONAL-ACTIVITY IN THE VISUAL-CORTEX

A novel near-infrared (NIR) spectrophotometry system with microprobes of optical transmitter and receivers (550 and 410 mu m in diameter, re spectively) has been developed. A three-dimensional profile of the sig nal source estimated in in vitro experiments showed two spindle-shaped regions around the respective probes, suggesting that the signal dete cted by the present system comes from a relatively restricted region a round each probe. Next, we examined how the concentration of oxygen in inspired gas affected the NIR signals in the rat cerebral cortex in v ivo. Calculated concentrations of oxyhemoglobin (HbO(2)) and deoxyhemo globin (Hb) in the rat cortex changed in mirror-image fashion in respo nse to the change in the O-2 concentration in the inspired gas. Finall y, NIR responses to visual stimulation were recorded from the striate cortex of conscious adult cats that had been monocularly deprived sinc e the peak of the sensitive period. Corresponding to the results of pr evious electrophysiological studies, stimulation of the normal eye ind uced significant NIR signals, whereas that of the deprived eye evoked no response. These results indicate that this new NIR system can be ap plied to study changes in oxygen metabolism in relatively restricted r egions following neuronal activation in the brain. (C) 1997 Elsevier S cience Ireland Ltd.