Abstract
Episodic retrieval is thought to involve reactivation of cortical regions that support encoding. The fidelity of our memories is putatively related to how well target memories are selectively reactivated during retrieval attempts. The present study employed multivoxel pattern analysis (MVPA) of fMRI data from a visual memory task to assess how neural measures of cortical reactivation relate to episodic retrieval. We used a paradigm in which individual cue words (nouns) were associated with photographs of well-known faces and/or scenes. Cue words were associated with either a face, scene, or both. Subjects were then presented with the cue word alone and attempted to retrieve the most recently studied photograph associated with each word. Competition–and the demand for selective retrieval–existed whenever a cue word was associated with multiple images. Behavioral results indicated high levels of overall retrieval success, but competitive retrieval was associated with lower recall rates and lower levels of retrieval detail. Pattern classification analyses indicated that patterns of activity in ventral temporal cortex that were elicited during encoding were robustly reactivated during retrieval–that is, classification of the category of retrieved items (face vs. scene) was well above chance. Indeed, the degree of reactivation revealed by pattern analysis increased as a function of retrieval detail that subjects reported, suggesting a link between reactivation and the phenomenology of visual remembering. Moreover, high levels of retrieval detail were associated with increased activation in the hippocampus, suggesting a role for the hippocampus in supporting detailed retrieval and cortical reactivation. Finally, the behavioral costs associated with competition between images were also reflected in neural measures of ventral temporal reactivation, as classification success was poorer when cue words were associated with multiple images. These results demonstrate a tight link between the subjective experience of visual remembering and neural evidence of perceptual reactivation.
This research was supported by research grants NIMH 5R01-MH080309 to A.D.W. and NIH R01-EY014193 and P30-EY000785 to M.M.C.