Default mode network connectivity indicates episodic memory capacity in mesial temporal lobe epilepsy.
OBJECTIVE
The clinical relevance of resting state functional connectivity in neurologic disorders, including mesial temporal lobe epilepsy (mTLE), remains unclear. This study investigated how connectivity in the default mode network changes with unilateral damage to one of its nodes, the hippocampus (HC), and how such connectivity can be exploited clinically to characterize memory deficits and indicate postsurgical memory change.


METHODS
Functional magnetic resonance imaging (fMRI) resting state scans and neuropsychological memory assessments (Warrington Recognition Tests for Words and Faces) were performed on 19 healthy controls, 20 patients with right mTLE, and 18 patients with left mTLE. In addition, postsurgical fMRI resting state and memory change (postsurgical memory performance-presurgical memory performance) data were available for half of these patients.


RESULTS
Patients with mTLE showed reduced connectivity from the posterior cingulate cortex (PCC) to the epileptogenic HC and increased PCC connectivity to the contralateral HC. Stronger PCC connectivity to the epileptogenic HC was associated with better presurgical memory and with greater postsurgical memory decline. Stronger PCC connectivity to the contralateral HC was associated with less postsurgical memory decline. Following surgery, PCC connectivity to the remaining HC increased from presurgical values and showed enhanced correlation with postsurgical memory function. It is notable that this index was superior to others (hippocampal volume, preoperative memory scores) in explaining variance in memory change following surgery.


CONCLUSIONS
Our results demonstrate the striking clinical significance of the brain's intrinsic connectivity in evaluating cognitive capacity and indicating the potential of postsurgical cognitive morbidity in patients with mTLE.
Krembil Neuroscience Center & Toronto Western Research Institute, University Health Network, Toronto, Ontario, Canada. cornelia.mccormick@gmail.com
Cornelia
C
McCormick
Maher
M
Quraan
Melanie
M
Cohn
Taufik A
TA
Valiante
Mary Pat
MP
McAndrews
D000328:Adult; D001931:Brain Mapping; D004569:Electroencephalography; D004833:Epilepsy, Temporal Lobe / Q000150:complications*; D005260:Female; D007839:Functional Laterality; D006624:Hippocampus / Q000098:blood supply / Q000473:pathology* / Q000503:physiopathology; D006801:Humans; D007091:Image Processing, Computer-Assisted; D008279:Magnetic Resonance Imaging; D008297:Male; D008569:Memory Disorders / Q000209:etiology* / Q000473:pathology*; D008875:Middle Aged; D009434:Neural Pathways / Q000098:blood supply / Q000473:pathology* / Q000503:physiopathology; D009483:Neuropsychological Tests; D010100:Oxygen / Q000097:blood; D011237:Predictive Value of Tests
D010100:Oxygen