title: Time-resolved measurements of brain activation after a short visual stimulus: new results on the physiological mechanisms of the cortical response.
abstract: This paper presents examinations of the time course of the signal from the visual cortex following a brief (2 s) light stimulus. Signal was generated from a 2 x 2 x 2 ml voxel using a modified point-resolved spectroscopy experiment. In accordance with previous studies a triphasic time course was observed. The results indicate that the observable signal contains contributions from non blood oxygen level dependent signal changes occurring immediately after the onset of stimulation. The response 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 the 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 common origin of the signals in the activated cortical areas.
authors.affiliation: Abt. Röntgendiagnostik, MR-Tomographie, Freiburg, Germany.
authors.forename: C
authors.initials: C
authors.lastname: Janz
authors.forename: O
authors.initials: O
authors.lastname: Speck
authors.forename: J
authors.initials: J
authors.lastname: Hennig
mesh_terms: D000328:Adult; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D010100:Oxygen / Q000097:blood; D010775:Photic Stimulation; D013997:Time Factors; D014793:Visual Cortex / Q000098:blood supply / Q000502:physiology*; D014796:Visual Perception / Q000502:physiology*
chemical_list: D010100:Oxygen