We have developed a variety of tasks to activate regions of interest in functional neuroimaging studies. 1. Using the n-back task we found a physiologic concomitant of capacity limitation in short-term memory. Key voxels in prefrontal cortex showed signal intensity plateaus or decreases with increasing load, not increases as might have been predicted. We are now examining the effects of pharmacological manipulation so in this system. First we are administering the indirect dopamine agonist amphetamine in normal controls in an attempt to increase capacity. Second we are using the NMDA antagonist ketamine to model capacity limitations in normal controls. 2. We developed a carefully matched set of verbal fluency tasks to examine the relation between semantic processing, thought disorder, and neurophysiology in schizophrenia using PET CBF methods. 3. To examine the levels of processing account of episodic memory we devised a series or recognition memory tasks. We also paid special attention to the development of a control task that would not involve active processing in the hope of better observing hippocampal activation.
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