title: Factors affecting reorganisation of memory encoding networks in temporal lobe epilepsy.
abstract: OBJECTIVE
  In temporal lobe epilepsy (TLE) due to hippocampal sclerosis reorganisation in the memory encoding network has been consistently described. Distinct areas of reorganisation have been shown to be efficient when associated with successful subsequent memory formation or inefficient when not associated with successful subsequent memory. We investigated the effect of clinical parameters that modulate memory functions: age at onset of epilepsy, epilepsy duration and seizure frequency in a large cohort of patients.
  
  
  METHODS
  We studied 53 patients with unilateral TLE and hippocampal sclerosis (29 left). All participants performed a functional magnetic resonance imaging memory encoding paradigm of faces and words. A continuous regression analysis was used to investigate the effects of age at onset of epilepsy, epilepsy duration and seizure frequency on the activation patterns in the memory encoding network.
  
  
  RESULTS
  Earlier age at onset of epilepsy was associated with left posterior hippocampus activations that were involved in successful subsequent memory formation in left hippocampal sclerosis patients. No association of age at onset of epilepsy was seen with face encoding in right hippocampal sclerosis patients. In both left hippocampal sclerosis patients during word encoding and right hippocampal sclerosis patients during face encoding, shorter duration of epilepsy and lower seizure frequency were associated with medial temporal lobe activations that were involved in successful memory formation. Longer epilepsy duration and higher seizure frequency were associated with contralateral extra-temporal activations that were not associated with successful memory formation.
  
  
  CONCLUSIONS
  Age at onset of epilepsy influenced verbal memory encoding in patients with TLE due to hippocampal sclerosis in the speech-dominant hemisphere. Shorter duration of epilepsy and lower seizure frequency were associated with less disruption of the efficient memory encoding network whilst longer duration and higher seizure frequency were associated with greater, inefficient, extra-temporal reorganisation.
authors.affiliation: Department of Clinical and Experimental Epilepsy, UCL Institute of Neurology, Queen Square, London WC1 N 3BG, UK; Epilepsy Society MRI Unit, Chesham Lane, Chalfont St. Peter SL9 0RJ, UK. Electronic address: m.sidhu@ucl.ac.uk.
authors.forename: M K
authors.initials: MK
authors.lastname: Sidhu
authors.affiliation: Department of Clinical and Experimental Epilepsy, UCL Institute of Neurology, Queen Square, London WC1 N 3BG, UK; Epilepsy Society MRI Unit, Chesham Lane, Chalfont St. Peter SL9 0RJ, UK. Electronic address: j.stretton@ucl.ac.uk.
authors.forename: J
authors.initials: J
authors.lastname: Stretton
authors.affiliation: Department of Clinical and Experimental Epilepsy, UCL Institute of Neurology, Queen Square, London WC1 N 3BG, UK; Epilepsy Society MRI Unit, Chesham Lane, Chalfont St. Peter SL9 0RJ, UK. Electronic address: g.winston@ucl.ac.uk.
authors.forename: G P
authors.initials: GP
authors.lastname: Winston
authors.affiliation: Department of Clinical and Experimental Epilepsy, UCL Institute of Neurology, Queen Square, London WC1 N 3BG, UK; Epilepsy Society MRI Unit, Chesham Lane, Chalfont St. Peter SL9 0RJ, UK. Electronic address: m.symms@ucl.ac.uk.
authors.forename: M
authors.initials: M
authors.lastname: Symms
authors.affiliation: Department of Clinical and Experimental Epilepsy, UCL Institute of Neurology, Queen Square, London WC1 N 3BG, UK; Epilepsy Society MRI Unit, Chesham Lane, Chalfont St. Peter SL9 0RJ, UK. Electronic address: p.thompson@ucl.ac.uk.
authors.forename: P J
authors.initials: PJ
authors.lastname: Thompson
authors.affiliation: Department of Clinical and Experimental Epilepsy, UCL Institute of Neurology, Queen Square, London WC1 N 3BG, UK; Epilepsy Society MRI Unit, Chesham Lane, Chalfont St. Peter SL9 0RJ, UK. Electronic address: m.koepp@ucl.ac.uk.
authors.forename: M J
authors.initials: MJ
authors.lastname: Koepp
authors.affiliation: Department of Clinical and Experimental Epilepsy, UCL Institute of Neurology, Queen Square, London WC1 N 3BG, UK; Epilepsy Society MRI Unit, Chesham Lane, Chalfont St. Peter SL9 0RJ, UK. Electronic address: j.duncan@ucl.ac.uk.
authors.forename: J S
authors.initials: JS
authors.lastname: Duncan
mesh_terms: D000328:Adult; D017668:Age of Onset; D004833:Epilepsy, Temporal Lobe / Q000209:etiology / Q000473:pathology / Q000503:physiopathology*; D005145:Face; D005260:Female; D007839:Functional Laterality; D006624:Hippocampus / Q000473:pathology / Q000503:physiopathology; D006801:Humans; D008279:Magnetic Resonance Imaging; D008297:Male; D008568:Memory / Q000502:physiology*; D008875:Middle Aged; D009434:Neural Pathways / Q000473:pathology / Q000503:physiopathology; D009483:Neuropsychological Tests; D010364:Pattern Recognition, Visual / Q000502:physiology; D010775:Photic Stimulation; D011932:Reading; D012598:Sclerosis; D012640:Seizures / Q000209:etiology / Q000473:pathology / Q000503:physiopathology; D013997:Time Factors; D055815:Young Adult
keywords: Duration; Episodic memory; Functional MRI; Seizure frequency; Temporal lobe epilepsy