Intracranial recordings and human memory

Abstract

Recent work involving intracranial recording during human memory performance provides superb spatiotemporal resolution on mnemonic processes. These data demonstrate that the cortical regions identified in neuroimaging studies of memory fall into temporally distinct networks and the hippocampal theta activity reported in animal memory literature also plays a central role in human memory. Memory is linked to activity at multiple interacting frequencies, ranging from 1 to 500Hz. High-frequency responses and coupling between different frequencies suggest that frontal cortex activity is critical to human memory processes, as well as a potential key role for the thalamus in neocortical oscillations. Future research will inform unresolved questions in the neuroscience of human memory and guide creation of stimulation protocols to facilitate function in the damaged brain.

Figure 1

Normalized power difference plots for the contrast of subsequently remembered > forgotten words in the rhinal cortex (left) and hippocampus (right) reported in [28]. Power increases are shown primarily in the theta and alpha bands prior to stimulus presentation at encoding. Adapted from [28].

Figure 2

Individual subdural recording sites from the patients studied in [30]; blue, prefrontal; green, parietal; orange, precuneus; yellow, parahippocampal. The red oscillation (1-4 Hz) represents coherence between brain regions during spatial memory and the orange oscillation (7- 10 Hz) represents coherence between these regions during temporal memory. Adapted from [30,31].