TIME-RESOLVED MEASUREMENTS OF BRAIN ACTIVATION AFTER A SHORT VISUAL STIMULUS - NEW RESULTS ON THE PHYSIOLOGICAL-MECHANISMS OF THE CORTICAL RESPONSE

This paper presents examinations of the time course of the signal from the visual cartes following a brief (2 s) light stimulus, Signal was generated from a 2x2x2 ml voxel using a modified point-resolved spectr oscopy experiment. In accordance with previous studies a triphasic tim e course was observed. The results indicate that the observable signal contains contributions from wan blood oxygen level dependent signal c hanges occurring immediately after the onset of stimulation, The respo nse to multiple stimuli could be fitted with a response model which is linear with respect to the BOLD-phase of the response, This suggests that the experiments using a very weak stimulus were performed below t he limit of the arterial reserve, This is in marked contrast to other studies performed by functional magnetic resonance imaging as well as optical imaging, First results using echo planar imaging confirm the c ommon origin of the signals in the activated cortical areas. (C) 1997 John Wiley & Sons, Ltd.