PET STUDIES OF MEMORY - NOVEL VERSUS PRACTICED FREE-RECALL OF WORD LISTS .2.

Positron emission tomography (PET) with the tracer (H2O)-O-15 was used to measure regional cerebral blood flow in 13 healthy volunteers whil e they engaged in free recall of 15-item word lists from the Rey Audit ory Verbal Learning task. The study was designed so that recall of wel l-practiced versus novel material could be compared. One week before t he PET study, subjects were trained to perfect recall of List A, while they were exposed to list B only 60 s prior to PET data acquisition. As in the companion study of free recall of complex narratives, we obs erved that practice tended to decrease the size of activations in regi ons involved in the memory component of the task; we also observed tha t the novel recall task produced greater activation in left frontal re gions, probably due to active encoding, A commonality of other regions observed in this pair of studies, as well as other studies of memory in the literature, suggests that the human brain may contain a distrib uted multinodal general memory system. Nodes on this network include t he frontal, parietal, and temporal cortices, the thalamus, the anterio r and posterior cingulate, the precuneus, and the cerebellum, There ap pears to be a commonality of components across tasks (e.g., retrieval, encoding) that is independent of content, as well as differentiation of some components that may be content-specific or task-specific. In a ddition, these results support a significant role for the cerebellum i n cognitive functions such as memory. (C) 1995 Academic Press, Inc.