Replay of cortical spiking sequences during human memory retrieval

Human brain activity during memory Animal studies suggest that sequence replay of neuronal activity may underlie memory retrieval and consolidation. However, there is no direct evidence that the replay of spiking activity sequences is important for these processes in the human brain. Vaz et al. simultaneously recorded single-unit spikes, local field potential, and intracranial electroencephalography signals in the brain while participants performed a memory task. Sharp wave ripple oscillations in the temporal lobe cortex reflected bursts of neural spiking, and these bursts of spikes organized into sequences during memory formation. These sequences were replayed during successful memory retrieval. The extent of sequence replay during correct recall was related to the extent to which cortical spiking activity was coupled with ripples in the medial temporal lobe. Science, this issue p. 1131 Human single-unit and local field potential recordings of encoding-related activity sequences during long-term memory formation and retrieval are investigated. Episodic memory retrieval is thought to rely on the replay of past experiences, yet it remains unknown how human single-unit activity is temporally organized during episodic memory encoding and retrieval. We found that ripple oscillations in the human cortex reflect underlying bursts of single-unit spiking activity that are organized into memory-specific sequences. Spiking sequences occurred repeatedly during memory formation and were replayed during successful memory retrieval, and this replay was associated with ripples in the medial temporal lobe. Together, these data demonstrate that human episodic memory is encoded by specific sequences of neural activity and that memory recall involves reinstating this temporal order of activity.