title: Functional connectivity of the hippocampus in temporal lobe epilepsy: feasibility of a task-regressed seed-based approach.
abstract: OBJECTIVE
  Resting-state functional connectivity (FC) has revealed marked network dysfunction in patients with temporal lobe epilepsy (TLE) compared to healthy controls. However, the nature and the location of these changes have not been fully elucidated nor confirmed by other methodologies. We assessed the presence of hippocampal FC changes in TLE based on the low frequency residuals of task-related functional magnetic resonance imaging data after the removal of task-related activation [i.e., task-regressed functional connectivity MRI (fcMRI)].
  
  
  METHODS
  We employed a novel, task-regressed approach to quantify hippocampal FC, and compare hippocampal FC in 17 patients with unilateral TLE (9 left) with 17 healthy controls.
  
  
  RESULTS
  Our results suggest widespread FC reductions in the mesial cortex associated with the default mode network (DMN), and some local FC increases in the lateral portions of the right hemisphere. We found more pronounced FC decreases in the left hemisphere than in the right, and these FC decreases were greatest in patients with left TLE. Moreover, the FC reductions observed between the hippocampus and posterior cingulate, inferior parietal, paracentral regions are in agreement with previous resting state studies.
  
  
  CONCLUSIONS
  Consistent with the existing literature, FC reductions in TLE appear widespread with prominent reductions in the medial portion of the DMN. Our data expand the literature by demonstrating that reductions in FC may be greatest in the left hemisphere and in patients with left TLE. Overall, our findings suggest that task-regressed FC is a viable alternative to resting state and that future studies may extract similar information on network connectivity from already existing datasets.
authors.affiliation: 1 Department of Psychiatry, University of California , San Diego, California.
authors.forename: Nuri Erkut
authors.initials: NE
authors.lastname: Kucukboyaci
authors.forename: Nobuko
authors.initials: N
authors.lastname: Kemmotsu
authors.forename: Chris E
authors.initials: CE
authors.lastname: Cheng
authors.forename: Holly M
authors.initials: HM
authors.lastname: Girard
authors.forename: Evelyn S
authors.initials: ES
authors.lastname: Tecoma
authors.forename: Vicente J
authors.initials: VJ
authors.lastname: Iragui
authors.forename: Carrie R
authors.initials: CR
authors.lastname: McDonald
mesh_terms: D000293:Adolescent; D000328:Adult; D001931:Brain Mapping / Q000379:methods; D016022:Case-Control Studies; D004833:Epilepsy, Temporal Lobe / Q000503:physiopathology*; D005260:Female; D007839:Functional Laterality / Q000502:physiology; D006624:Hippocampus / Q000503:physiopathology*; D006801:Humans; D007091:Image Processing, Computer-Assisted; D008279:Magnetic Resonance Imaging / Q000379:methods; D008297:Male; D008875:Middle Aged; D009415:Nerve Net / Q000503:physiopathology*; D009434:Neural Pathways / Q000503:physiopathology; D013702:Temporal Lobe / Q000503:physiopathology*; D055815:Young Adult