title: Functional substrate for memory function differences between patients with left and right mesial temporal lobe epilepsy associated with hippocampal sclerosis.
abstract: OBJECTIVE
  Little is known about the functional substrate for memory function differences in patients with left or right mesial temporal lobe epilepsy (mTLE) associated with hippocampal sclerosis (HS) from an electrophysiological perspective. To characterize these differences, we hypothesized that hippocampal theta connectivity in the resting-state might be different between patients with left and right mTLE with HS and be correlated with memory performance.
  
  
  METHODS
  Resting-state hippocampal theta connectivity, identified via whole-brain magnetoencephalography, was evaluated. Connectivity and memory function in 41 patients with mTLE with HS (left mTLE=22; right mTLE=19) were compared with those in 46 age-matched healthy controls and 28 patients with focal cortical dysplasia (FCD) but without HS.
  
  
  RESULTS
  Connectivity between the right hippocampus and the left middle frontal gyrus was significantly stronger in patients with right mTLE than in patients with left mTLE. Moreover, this connectivity was positively correlated with delayed verbal recall and recognition scores in patients with mTLE. Patients with left mTLE had greater delayed recall impairment than patients with right mTLE and FCD. Similarly, delayed recognition performance was worse in patients with left mTLE than in patients with right mTLE and FCD. No significant differences in memory function between patients with right mTLE and FCD were detected. Patients with right mTLE showed significantly stronger hippocampal theta connectivity between the right hippocampus and left middle frontal gyrus than patients with FCD and left mTLE.
  
  
  CONCLUSIONS
  Our results suggest that right hippocampal-left middle frontal theta connectivity could be a functional substrate that can account for differences in memory function between patients with left and right mTLE. This functional substrate might be related to different compensatory mechanisms against the structural hippocampal lesions in left and right mTLE groups. Given the positive correlation between connectivity and delayed verbal memory function, hemispheric-specific hippocampal-frontal theta connectivity assessment could be useful as an electrophysiological indicator of delayed verbal memory function in patients with mTLE with HS.
authors: Neuroscience Research Institute, Seoul National University College of Medicine, Seoul, Republic of Korea.
authors: Seung-Hyun
authors: SH
authors: Jin
authors: Neuroscience Research Institute, Seoul National University College of Medicine, Seoul, Republic of Korea; Department of Neurosurgery, Seoul National University Hospital, Seoul, Republic of Korea; Department of Neurosurgery, Seoul National University College of Medicine, Seoul, Republic of Korea; Department of Brain and Cognitive Sciences, Seoul National University College of Natural Sciences, Seoul, Republic of Korea. Electronic address: chungc@snu.ac.kr.
authors: Chun Kee
authors: CK
authors: Chung
mesh_terms: D000293:Adolescent; D000328:Adult; D004569:Electroencephalography; D004833:Epilepsy, Temporal Lobe / Q000150:complications* / Q000473:pathology / Q000523:psychology*; D005260:Female; D005625:Frontal Lobe / Q000473:pathology; D007839:Functional Laterality; D006624:Hippocampus / Q000473:pathology*; D006801:Humans; D008279:Magnetic Resonance Imaging; D015225:Magnetoencephalography; D008297:Male; D054220:Malformations of Cortical Development / Q000473:pathology / Q000523:psychology; D008568:Memory; D011939:Mental Recall; D008875:Middle Aged; D009415:Nerve Net / Q000473:pathology; D009434:Neural Pathways; D009483:Neuropsychological Tests; D021641:Recognition, Psychology; D012598:Sclerosis; D013826:Theta Rhythm; D055815:Young Adult
keywords: Functional substrate; Hippocampal sclerosis; Memory; Mesial temporal lobe epilepsy; Resting-state magnetoencephalography