PREFRONTAL CORTEX AND RECOGNITION MEMORY - FUNCTIONAL-MRI EVIDENCE FOR CONTEXT-DEPENDENT RETRIEVAL-PROCESSES

Functional neuroimaging studies of episodic recognition memory consist ently demonstrate retrieval-associated activation in right prefrontal regions, including the right anterior and right dorsolateral prefronta l cortices, In theory, these activations could reflect processes assoc iated with retrieval success, retrieval effort or retrieval attempt; e ach of these hypotheses has some support from previous studies. In Exp eriment 1, we examined these functional interpretations using function al MRI to measure prefrontal activation across multiple levels of reco gnition performance. Results revealed similar patterns of right prefro ntal activation across varying levels of retrieval success and retriev al effort, suggesting that these activations reflect retrieval attempt , Retrieval attempt may include initiation of retrieval search or eval uation of the products of retrieval, such as scrutiny of specific attr ibutes of the test item in an effort to determine whether it was encou ntered previously, In Experiment 2, we examined whether engagement of retrieval attempt is context-dependent by varying the context in which retrieval was performed; this was done by changing test instructions. Importantly, study and test stimuli were held constant, with only the test instructions varying across conditions, Results revealed that th e pattern of right prefrontal activation varied across retrieval conte xts. Collectively, these experiments suggest that right prefrontal reg ions mediate processes associated with retrieval attempt, with the pro bability of engaging these regions depending upon the retrieval contex t. Conflicting results across previous studies may be reconciled if th e influence of retrieval context on the adopted retrieval strategy is considered. Finally these results suggest that right prefrontal region s activated during recognition are not critical for successful perform ance as similar magnitudes of activation were present across multiple levels of performance. These findings reconcile imaging results with t he selective effects of prefrontal lesions on retrieval-intensive epis odic memory tests.