Event-related potential studies of associative recognition and recall: electrophysiological evidence for context dependent retrieval processes

To investigate the neural correlates of episodic recollection the ERP corre lates of memory for new associations (recently studied novel word pairs) we re investigated using two tasks, associative recognition and associative re call. For the recognition task subjects discriminated old from new word pai rs and, for pairs judged old, reported whether the pairs were intact or rec ombined (compared to at study). For the recall task, subjects discriminated old from new words and, for each word judged old, reported its study assoc iate. ERPs were recorded at test from 25 scalp electrodes, with a 1944-ms r ecording epoch. In Experiment 1, the tasks were randomly interleaved. Consi stent with previous findings, relative to the ERPs for correctly classified new items, the ERP correlates of successful associative recognition consis ted of a sustained left parietal positivity, and two frontal positivities, one early and bilateral, the other occurring later and showing a right-side d maximum. In contrast to previous findings, successful associative recall elicited similar effects to those found for recognition. Topographic analys es revealed that the distribution of these retrieval-related ERP effects we re similar across the two tasks, suggesting that the recognition and recall of associative information gives rise to activity in overlapping, if not t he same, neural populations. In Experiment 2 the tasks were blocked. In con trast to the findings of Experiment 1, successful associative recall elicit ed left parietal and late onsetting right frontal positivities, in the abse nce of the early bilateral frontal positivity. This finding suggests that f rontally-distributed memory-related ERP effects are both neurally and funct ionally dissociable. Specifically, we argue that the functional significanc e of the early frontally distributed ERP effect cannot be accounted for by the 'post-retrieval processing' hypothesis that is taken to account for the late right frontal effect, suggesting that episodic recollection itself is neither neurally nor functionally homogenous. (C) 1999 Published by Elsevi er Science B.V. All rights reserved.