Abstracts

Rationale: Models of episodic memory formation suggest that when targeting a memory, the neural mechanisms that are engaged during retrieval reinstate activity present during encoding. Empiric evidence for neural reinstatement has largely emerged from functional imaging studies, but the precise spatiotemporal dynamics underlying these processes are poorly understood. Methods: We used intracranial recordings to directly examine the spatiotemporal extent of neural reinstatement as 32 participants with electrodes placed for seizure monitoring performed a paired associates task. Results: We found significantly greater reinstatement of the distributed pattern of oscillatory power during trials that exhibited successful encoding and retrieval compared to incorrect trials. Our results provide evidence for temporal context reinstatement, temporal drift, reinstatement as a correlate of memory strength, and the facilitation of reinstatement by the hippocampus. Furthermore, we quantified the reinstatement of the neural activity in individual frequency bands from individual electrodes and found that reinstatement was largely mediated by theta and high gamma frequencies in the temporal lobes. Leveraging the high temporal precision afforded by intracranial recordings, we found that high gamma activity associated with reinstatement preceded theta activity during encoding, but during retrieval this difference in timing between frequency bands was absent. Conclusions: Our approach capitalizes on the sensitivity of examining multivariate activity and our data demonstrate that patterns of spectral power distributed across multiple spatial locations and multiple frequency bands are reinstated during memory retrieval. Understanding the temporal dynamics and spatial distribution governing the reinstatement of neural processes that are relevant for successful memory encoding and retrieval has important implications for understanding how patterns of cortical activity are coordinated to create, and then to retrieve, a coherent memory trace