J. Hennig et al., FUNCTIONAL SPECTROSCOPY OF BRAIN ACTIVATION FOLLOWING A SINGLE LIGHT-PULSE - EXAMINATIONS OF THE MECHANISM OF THE FAST INITIAL RESPONSE, International journal of imaging systems and technology, 6(2-3), 1995, pp. 203-208
Localized proton spectroscopy using the PRESS sequence was performed t
o measure the free induction decay of the water signal in a 2 x 2 x 2
= ml voxel located in the visual cortex after a short light pulse. The
experiment was run continuously with a repetition time of 400 ms; the
onset of the light pulse was triggered by the spectrometer. The FIDs
were measured as a function of the echo time (TE) and the length of th
e stimulus (TS). The time course showed three different phases: An ini
tial response was observed 400 ms after the onset of the stimulus, whi
ch was demonstrated to be mainly a change in the apparent spin density
and/or T-1 with a minor contribution of T-2. No significant change i
n T-2 could be measured. Changes in the ionic cell environment and/or
the subsequent increase in cell size upon stimulation are discussed as
a potential mechanism for the observed signal response. (C) 1995 John
Wiley & Sons, Inc.