Choice-predictive activity in parietal cortex during source memory decisions.

Neurobiological research has classically focused on perceptual decision-making, although many real-life decisions are based on information that is not currently available but stored in long-term memory. Previous studies have suggested that the lateral parietal cortex encodes decision-related signals during item recognition judgments. In the present fMRI study, we employed a parametric manipulation of evidence for source memory judgments and tested several hypotheses concerning memory decision signals in parietal cortex. As expected, the mean BOLD signal in several parietal regions was modulated by decision evidence. An analysis of the locally distributed pattern of activity, moreover, identified a parietal cluster showing significant choice-predictive activity even at the lowest level of decision evidence, with decoding accuracy that increased as a function of evidence. Decoding patterns were consistent across subjects as shown by a leave-one-subject-out classification analysis. Finally, we found that the pattern of choice-predictive activity in parietal lobe was temporally correlated with that observed in medial temporal regions traditionally associated with long-term memory functions. The present findings are consistent with a general role of lateral parietal regions located around the intraparietal sulcus in representing a decision variable for memory-based decisions.