POSITRON-EMISSION TOMOGRAPHY IMAGING OF LONG-TERM SHAPE-RECOGNITION CHALLENGES

Long-term visual memory performance was impaired by two types of chall enges: a diazepam challenge on acquisition and a sensory challenge on recognition. Using positron-emission tomography regional cerebral bloo d flow imaging, we studied the effect of these challenges on regional brain activation during the delayed recognition of abstract visual sha pes as compared with a baseline fixation task. Both challenges induced a significant decrease in differential activation in the left fusifor m gyrus, suggesting that this region is involved in the automatic or v olitional comparison of incoming and stored stimuli. In contrast, thal amic differential activation increased in response to memory challenge s. This increase might reflect enhanced retrieval attempts as a compen satory mechanism for restoring recognition performance.