Abstract We used Positron Emission Tomography to map the neural substrate of human short-term memory for orientation, de®ned as retaining a single orientation in memory over a long delay, by comparing a successive discrimination task with a 6-s delay to the same task with a brief 0.3 s delay and to an identi®cation control task. Short-term memory engaged the superior parietal lobe bilaterally, the middle occipital gyrus bilaterally and the left dorsolateral prefrontal cortex. In addition, we studied the resistance to a distractor item by comparing the successive discrimination task with long delay, with and without an intervening distractor stimulus. This manipulative process engaged left ventral premotor cortex and left dorsolateral prefrontal cortex. The activation of left dorsolateral prefrontal cortex is interpreted as re¯ecting co-ordination between task components. These results, combined with those of two previous studies using an identical reduction strategy, underscore the functional heterogeneity in the prefrontal cortex during short-term and working memory
