NEURAL CORRELATES OF MEMORY RETRIEVAL DURING RECOGNITION MEMORY AND CUED-RECALL

Regional brain activity, measured by (H2O)-O-15 PET, was investigated during recognition memory and word-stem cued recall of words in order to compare the neural correlates of two components of memory retrieval -effort and success-as a function of task. For each task there was a b aseline and two retrieval conditions. In one retrieval condition (zero density), none of the test items corresponded to words encoded in a p receding study phase. Differences in activity between this condition a nd the baseline were employed to characterize the neural correlates of retrieval effort in each task. In the other retrieval condition (high density), 80% of the test items had been studied previously. Differen ces in brain activity between this condition and the zero-density cond ition were taken to represent the neural correlates of successful retr ieval. The principal findings concern the right anterior prefrontal co rtex, a region demonstrated previously to be active during episodic re trieval. Relative to baseline, this region showed no evidence of activ ation in the zero-density condition of the recognition task, but did s how enhanced activity in the equivalent condition of the cued-recall t ask. In contrast, relative to the zero-density condition, the high-den sity condition was associated with increased right prefrontal activity during recognition, but reduced activity during cued recall. It is pr oposed that the right prefrontal cortex supports cognitive processes t hat operate on information retrieved in response to a test item and th at these processes contribute to the evaluation of whether the informa tion represents an appropriate prior episode. (C) 1998 Academic Press.