The hippocampus as the switchboard between perception and memory

Abstract

Adaptive memory recall requires a rapid and flexible switch from external perceptual reminders to internal mnemonic representations. However, owing to the limited temporal or spatial resolution of brain imaging modalities used in isolation, the hippocampal–cortical dynamics supporting this process remain unknown. We thus employed an object-scene cued recall paradigm across two studies, including intracranial electroencephalography (iEEG) and high-density scalp EEG. First, a sustained increase in hippocampal high gamma power (55 to 110 Hz) emerged 500 ms after cue onset and distinguished successful vs. unsuccessful recall. This increase in gamma power for successful recall was followed by a decrease in hippocampal alpha power (8 to 12 Hz). Intriguingly, the hippocampal gamma power increase marked the moment at which extrahippocampal activation patterns shifted from perceptual cue toward mnemonic target representations. In parallel, source-localized EEG alpha power revealed that the recall signal progresses from hippocampus to posterior parietal cortex and then to medial prefrontal cortex. Together, these results identify the hippocampus as the switchboard between perception and memory and elucidate the ensuing hippocampal–cortical dynamics supporting the recall process.

Temporal dynamics of competition between statistical learning and episodic memory in intracranial recordings of human visual cortex

“…A strong candidate is the hippocampus and surrounding medial temporal lobe cortex. In addition to representing predictions ( Kok and Turk-Browne, 2018 ; Sherman and Turk-Browne, 2020 ), the hippocampus interfaces between perception and memory ( Treder et al, 2021 ) and has been shown to drive reinstatement of predicted information in visual cortex ( Bosch et al, 2014 ; Tanaka et al, 2014 ; Danker et al, 2017 ; Hindy et al, 2016 ).…”

A consensus statement on detection of hippocampal sharp wave ripples and differentiation from other fast oscillations

“…As in rodents, ripples are present in and near the CA1 pyramidal layer but not in other layers 98 . The oscillation frequency of ripples in primates is slower (110)(111)(112)(113)(114)(115)(116)(117)(118)(119)(120)(121)(122)(123)(124)(125) than in rodents. Concurrent with ripple occurrence, SPWs are present in the str.…”

“…Under physiological conditions, ripples are prominent in CA1 because of the strong convergent input from the CA2/3 pyramidal neurons along the septotemporal axis 27,29 . CA1 coupled ripples are present but decrease along the subicular-entorhinal axis 62,66,113 . Naturally-occurring fast oscillations can also be observed in dentate gyrus and CA3 pyramidal layer but they vary across a wide frequency range and their spike content is not phase-locked to the CA1 ripple 25 .…”

Reduced memory precision in older age is associated with functional and structural differences in the angular gyrus

“…In particular, a trend-level reduction in retrieval success effects was evident in the AG in the older group. Given emerging insights about the temporal sequence of hippocampal and parietal retrieval operations, with hippocampal signal reflecting successful retrieval preceding that of the posterior parietal cortex 54,55 , it is possible that such a reduction could reflect impoverished input from the HC to the rest of the posterior-medial network in ageing.…”