fMRI BOLD signals in the left angular gyrus and hippocampus are associated with memory precision

It has been proposed that the neural correlates of successful memory retrieval can be dissociated from the correlates of retrieval precision (fidelity). The specific findings supporting this proposal are, however, inconsistent across different studies. Here, functional magnetic resonance imaging (fMRI) was employed to examine these neural correlates in the context of a test of memory for spatial location that minimized temporal overlap between mnemonic and visuomotor processing. During the encoding phase, participants studied different object images, each placed at a random location on an invisible circle. At test, studied and new images were presented to the participants. The requirement was to make a covert recognition memory judgment to each image and to attempt to recall its studied location, guessing if necessary. A cue signaling the requirement to make a location memory judgment was presented 4 s after image onset. Memory precision was estimated as the angular difference between the originally studied location and the location signaled by the participant. In an analysis that combined the data from the present study and a closely similar prior study, we replicated prior reports that during retrieval fMRI BOLD activity in the left angular gyrus (AG) and the hippocampus tracks memory precision on a trial-wise basis. Linear mixed-effects modeling indicated that the activity in the two regions explained independent sources of variability in these judgments. In addition, multivoxel pattern similarity analysis revealed an item-level reinstatement effect (as indexed by encoding-retrieval overlap) in the left AG that was restricted to items associated with high precision judgments. These findings suggest that the hippocampus and the left AG play non-redundant roles in the retrieval and behavioral expression of high precision episodic memories.