A COMPARATIVE FLASH AND EPI STUDY OF REPETITIVE AND SUSTAINED VISUAL ACTIVATION

Functional responses to either brief repetitive or sustained activatio n of the human visual cortex (movie presentation) were monitored using both fast low angle shot and echo planar imaging sequences, To allow for proper comparisons, native image contrasts were equally sensitized to changes in cerebral blood oxygenation with other experimental cond itions matched as much as possible. Putative influences of receiver ba ndwidth and absolute voxel size were specifically addressed, In all ca ses resulting correlation maps and regional signal intensity time cour ses showed excellent spatial and temporal congruence, respectively, In particular, for a 6 min protocol of sustained activation, both FLASH and EPI yielded an initial signal increase (oxygenation overshoof), a subsequent signal decrease during ongoing stimulation, and a marked si gnal drop (oxygenation undershoot) after the end of stimulation, These findings exclude technical differences between FLASH and EPI as the s ource of previous contradictory observations more likely to be explain ed by differences in stimulus design. (C) 1997 John Wiley & Sons.