High gamma and beta band oscillations in left ventral posterior parietal cortex are regionally dissociated during verbal episodic encoding and recall

TL;DR

This study reveals a regional dissociation in the left ventral posterior parietal cortex during verbal memory encoding and recall, with distinct oscillatory patterns linked to external attention and internal memory processes.

Contribution

It uncovers a double dissociation in anterior and posterior VPC activity during encoding and recall, highlighting oscillatory differences related to memory success.

Findings

Anterior VPC activity correlates with encoding success.

Posterior VPC activity correlates with recall success.

High gamma and beta oscillations indicate attention and memory processes.

Abstract

The posterior parietal cortex (PPC) has a unique role in memory retrieval: fMRI and electrocorticography studies suggest that within the ventral PPC (VPC) specifically, there is an anterior-posterior functional divergence between externally-oriented and internally-oriented attention to memory (AtoM). However, the role of VPC during verbal episodic encoding, and the relationship between encoding- and retrieval-related activity, is less understood. Here we show that activation within a subregion of VPC is doubly dissociated between its anterior and posterior parts, during encoding compared to recall in a free recall task. We found that regional activation defined by increased high gamma power and decreased beta power oscillations during encoding and recall correlated with recall success. During word encoding, iEEG sites that showed this correlation were located anterior to those that showed deactivation. Conversely, during word recall, sites that showed stronger correlations between activity and number of words recalled were located more posteriorly. Our results demonstrate the significance of high gamma and beta oscillations suggesting a push-pull relationship between attention to external stimuli and internal memories within left ventral PPC. Knowledge of this divergence of function along the anterior-posterior axis within left ventral PPC may prove useful for guiding brain stimulation strategies.