Characterization of brain network supporting episodic memory in the absence of one medial temporal lobe

Abstract

How the brain supports normal episodic memory function without medial temporal lobe (MTL) structures has not been well characterized, which could provide clues for new therapeutic targets for people with MTL dysfunction‐related memory impairment. To characterize brain network supporting effective episodic memory function in the absence of unilateral MTL, we investigated the whole‐brain cortical interactions during functional magnetic resonance imaging memory encoding paradigms of words and figures in patients who showed a normal range of memory capacity following unilateral MTL resection and healthy controls (HC). Compared to the HC, the patients showed less activation in the left inferior frontal areas and right thalamus together with greater activation in the many cortical areas including the medial prefrontal cortex (mPFC). Task‐based functional connectivity (FC) analysis revealed that the mPFC showed stronger interactions with widespread brain areas in both patient groups, including the hippocampus contralateral to the resection. Moreover, the strength of the mPFC FC predicts the individual memory capacity of the patients. Our data suggest that hyperconnectivity of distributed brain areas, especially the mPFC, is a neural mechanism for memory function in the absence of one MTL.

Structural and Functional Alterations in the Contralesional Medial Temporal Lobe in Glioma Patients

“…MTL resection for the treatment of medically intractable temporal lobe epilepsy is commonly associated with episodic memory impairment after surgery (Pillon et al, 1999;Savage et al, 2002). In patients with a normal range of memory capacity following unilateral MTL resection, task-based functional connectivity analysis has revealed functional reorganization in the contralesional hippocampus and medial prefrontal cortex (Jeong et al, 2019). Recently, many studies have demonstrated that the MTL forms two functionally distinct memory circuits, with each circuit delineating distinct anatomical and functional connections to other related brain regions (Kahn et al, 2008;Fanselow and Dong, 2010;Poppenk and Moscovitch, 2011;Libby et al, 2012).…”

Dynamic Functional Connectivity Change-Point Detection With Random Matrix Theory Inference

“…gov/afni/). More details about the memory encoding paradigm and data preprocessing have been described elsewhere (Jeong et al, 2018(Jeong et al, , 2019. Since previous studies have shown that FC during the postencoding resting-state is related to the memory performance (Tambini et al, 2010;Staresina et al, 2013;Tambini and Davachi, 2013), we thought that data that showed evident FC changes of memory related areas rather than entire data of post-encoding resting-state may possibly provide the additional information of the memory consolidation network.…”

“…The same subjects from our previous study are used in this study except for one patient who showed a severe movement artifact (Jeong et al, 2019 ). Patients who underwent unilateral MTL resection (MTLR) to treat medically intractable temporal lobe epilepsy at Seoul National University Hospital at least 1 year before recruitment and were between 19 and 50 years of age are retrospectively recruited.…”

“…The resting-state functional data underwent a number of preprocessing steps including motion correction, slice time correction, co-registration, spatial normalization, and spatial smoothing (AFNI, version: 16.0.00, https://afni.nimh.nih.gov/afni/ ). More details about the memory encoding paradigm and data preprocessing have been described elsewhere (Jeong et al, 2018 , 2019 ).…”

“…The relationships between the behavioral accuracy (d-prime) of the in-scanner memory task and the FC values of post-encoding rest after change-point are also analyzed. Our previous study describes behavioral accuracy in detail (Jeong et al, 2019 ). Figure 3 shows the significant correlations.…”