Human rehearsal processes and the frontal lobes: PET evidence.

Our research is focused on working memory. This is a storage system that holds a limited amount of information for a brief time, with that information rapidly accessible and changeable from moment to moment. Such a system is essential for dealing with problems that require one to record features of a constantly changing environment, and to keep these features "on line" as they are used to guide behavior. Extensive research supports two basic claims about the neural implementation of working memory in both human and nonhuman primates: ( 1 ) Working memory is implemented in the brain by heightened neural activity in particular regions, which notably include prefrontal and parietal cortex;'.' and ( 2 ) different kinds of working memories correspond to different kinds of information. This is indicated by findings in nonhuman primates that neurons in different regions of the prefrontal cortex are active when monkeys have to store spatial information versus object information,' and by the PET findings with humans that different networks of cortical regions are active depending on whether people have to remember spatial, object, or verbal i n f ~ r m a t i o n . ~ In this paper, we emphasize human data, and try to go beyond the above two generalizations by decomposing each working memory into two basic constituents. We advance the following hypotheses: