Parietal cortex tracks the amount of information retrieved even when it is not the basis of a memory decision

Although the parietal cortex is not conventionally associated with memory, a large number of recent fMRI studies have suggested that that the parietal cortex may play a role in recognition memory. Activity in the lateral parietal cortex is correlated with the subjective impression that an item is old, It has therefore been proposed that the parietal cortex may be determining the outcome of the decision process. For instance, parietal cortex may be temporally integrating mnemonic information in favor of an old response until a decision criterion is reached (mnemonic accumulator hypothesis). Activity in the lateral parietal cortex also increases with the amount of information retrieved. It has thus been proposed that lateral parietal cortex may be acting as a working memory buffer into which retrieved information is transferred (output buffer hypothesis). In previous studies, confidence in an old decision and the amount of information retrieved have been confounded, thus making these competing hypotheses difficult to differentiate. We used a frequency discrimination paradigm to dissociate the amount of information retrieved from memory and decision certainty. We found that lateral and medial regions of parietal cortex previously implicated in recognition memory track the absolute amount of information retrieved even when this is not the basis of the recognition decision. Our results present a serious challenge to proposals that the parietal cortex contributes directly to the recognition decision process. (C) 2010 Elsevier Inc. All rights reserved.