Phase-Amplitude Coupling and Phase Synchronization Between Medial Temporal, Frontal and Posterior Brain Regions Support Episodic Autobiographical Memory Recall

Nicolas Roehri,Lucie Bréchet,Alvaro Pascual-Leone,Christoph M Michel,Martin Seeber

doi:10.1007/s10548-022-00890-4

Abstract

Episodic autobiographical memory (EAM) is a complex cognitive function that emerges from the coordination of specific and distant brain regions. Specific brain rhythms, namely theta and gamma oscillations and their synchronization, are thought of as putative mechanisms enabling EAM. Yet, the mechanisms of inter-regional interaction in the EAM network remain unclear in humans at the whole brain level. To investigate this, we analyzed EEG recordings of participants instructed to retrieve autobiographical episodes. EEG recordings were projected in the source space, and time-courses of atlas-based brain regions-of-interest (ROIs) were derived. Directed phase synchrony in high theta (7–10 Hz) and gamma (30–80 Hz) bands and high theta-gamma phase-amplitude coupling were computed between each pair of ROIs. Using network-based statistics, a graph-theory method, we found statistically significant networks for each investigated mechanism. In the gamma band, two sub-networks were found, one between the posterior cingulate cortex (PCC) and the medial temporal lobe (MTL) and another within the medial frontal areas. In the high theta band, we found a PCC to ventromedial prefrontal cortex (vmPFC) network. In phase-amplitude coupling, we found the high theta phase of the left MTL biasing the gamma amplitude of posterior regions and the vmPFC. Other regions of the temporal lobe and the insula were also phase biasing the vmPFC. These findings suggest that EAM, rather than emerging from a single mechanism at a single frequency, involves precise spatio-temporal signatures mapping on distinct memory processes. We propose that the MTL orchestrates activity in vmPFC and PCC via precise phase-amplitude coupling, with vmPFC and PCC interaction via high theta phase synchrony and gamma synchronization contributing to bind information within the PCC-MTL sub-network or valuate the candidate memory within the medial frontal sub-network.

Highlights

Episodic autobiographical memory (EAM) is a complex cognitive function that involves a specific large-scale network of interacting brain regions to store and later retrieve our lives' experiences
We found several statistically significant clusters of point sources in gamma and high theta bands when comparing the power in the memory condition to the control/math condition (Fig. 1, Table 1)
In the gamma band, the left AMY regions of interest (ROIs) was driven by other medial temporal lobe (MTL) regions (HIPP, parahippocampal gyrus (PHG)) and left posterior cingulate cortex (PCC), and the pSFG, anterior cingulate cortex (ACC), and ventromedial prefrontal cortex (vmPFC) were interconnected

Summary

Introduction

Episodic autobiographical memory (EAM) is a complex cognitive function that involves a specific large-scale network of interacting brain regions to store and later retrieve our lives' experiences. Brain oscillations and synchronization within and across large-scale networks facilitate long-distance communication and promote cognitive functions in the healthy human brain (Buzsáki 2006). Theta oscillations are the dominant rhythms recorded in the hippocampus (Buzsaki 2002) and appear to serve as a mechanism of EAM memories constituted of shorter sub-episodes, whose temporal dynamics during recall are supported by the same mechanism as during encoding (Buzsaki 2002; Buzsáki and Moser 2013). Theta oscillations have been associated with both encoding and retrieval of episodic memories (Friese et al 2013; Osipova et al 2006; Sederberg et al 2003)

Methods

Results

Discussion

Conclusion