Neural mechanisms of human episodic memory formation across spatial scales
Episodic memory relies upon our ability to retrieve the memory of individual events that we have experienced at a particular time and place. The hippocampus and structures in the medial temporal lobe (MTL) play a critical role in this process by representing relations between memories and the spatiotemporal context within which they occur. A parallel line of research, however, has demonstrated that successful episodic memory retrieval involves recovering neural representations that were present in the cortex when memories were first experienced. This has led to the hypothesis that the hippocampus and MTL may promote episodic memory retrieval through a dialogue with the cortex that facilitates the ability to recover these neural representations. Here we explore this hypothesis by examining neural signals directly captured from the human brain across multiple spatial scales as participants perform a verbal episodic memory task. We show that patterns of neural activity at both the larger mesoscopic scale of intracranial EEG (iEEG) electrodes and at the smaller microscale of single units in the temporal lobe cortex are reinstated when memories are successfully retrieved. Moreover, we show that that such reinstatement of cortical activity is locked to the occurrence of coordinated oscillatory activity between the temporal lobe cortex and structures in the MTL. Together, these data suggest a mechanistic framework through which neural activity in the MTL can promote memory retrieval by initiating the replay of patterns of neural activity in the cortex.
Dr. Kareen Zaghloul is an investigator in the Functional and Restorative Neurosurgery Unit at the National Institute of Neurological Disorders and Stroke, NIH.
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