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Updated: Feb 13, 2026
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Network Analysis of the Default Mode Network Using Functional Connectivity MRI in Temporal Lobe Epilepsy
Published on: August 5, 2014
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Task activation and functional connectivity show concordant memory laterality in temporal lobe epilepsy.
Noah Sideman1, Ganne Chaitanya1, Xiaosong He1
1Thomas Jefferson University, Department of Neurology, United States.
Epilepsy & Behavior : E&B
|March 3, 2018
Summary
In temporal lobe epilepsy, functional reorganization in the left hemisphere leads to rightward memory laterality. This shift in visual episodic memory is supported by altered functional connectivity, especially in left temporal lobe epilepsy.
Area of Science:
- Neuroscience
- Epilepsy Research
- Cognitive Neurology
Background:
- Mesial temporal lobe (MTL) function asymmetry in epilepsy impacts cognitive risk from neurosurgery.
- Previous studies used fMRI activation laterality index (LI) to assess visual episodic memory shifts in MTL structures.
- The concordance between activation-based LI and task-related functional connectivity (FC) in epilepsy remains underexplored.
Purpose of the Study:
- To investigate if task-related functional connectivity (FC) aligns with standard fMRI activation laterality measures in temporal lobe epilepsy (TLE).
- To examine visual episodic memory laterality patterns in patients with TLE compared to healthy controls.
Main Methods:
- fMRI scanning during a scene encoding task (SET) in 56 TLE patients (31 LTLE, 25 RTLE) and 34 healthy controls (HC).
- Assessment of activation-based laterality index (LI) for hippocampal gyrus (HG) and parahippocampal gyrus (PHG) during SET.
- Comparison of activation LI with task-related functional connectivity (FC) measures.
Main Results:
- Patients with left TLE (LTLE) showed a consistently higher, right-lateralized LI in HG and PHG compared to HC and right TLE (RTLE) groups, indicating functional reorganization.
- RTLE patients did not exhibit a clear contralateral shift; HG showed no laterality bias, and PHG had no LI shift.
- FC data in LTLE confirmed reorganization, with rightward LI linked to connections between left occipital/frontal regions and the right PHG, and between right HG and left frontal areas.
Conclusions:
- Altered laterality patterns in mesial temporal lobe epilepsy (MTLE) vary by seizure onset side and affected structures.
- Good correspondence between task LI activation and FC patterns in LTLE suggests that visual episodic memory reorganization requires both activation and connectivity shifts.
- Understanding these laterality patterns is crucial for predicting cognitive outcomes after epilepsy surgery.
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