title: The relationship between Hippocampal asymmetry and working memory processing in combat-related PTSD - a monozygotic twin study.
abstract: BACKGROUND
  PTSD is associated with reduction in hippocampal volume and abnormalities in hippocampal function. Hippocampal asymmetry has received less attention, but potentially could indicate lateralised differences in vulnerability to trauma. The P300 event-related potential component reflects the immediate processing of significant environmental stimuli and has generators in several brain regions including the hippocampus. P300 amplitude is generally reduced in people with PTSD.
  
  
  METHODS
  Our study examined hippocampal volume asymmetry and the relationship between hippocampal asymmetry and P300 amplitude in male monozygotic twins discordant for Vietnam combat exposure. Lateralised hippocampal volume and P300 data were obtained from 70 male participants, of whom 12 had PTSD. We were able to compare (1) combat veterans with current PTSD; (2) their non-combat-exposed co-twins; (3) combat veterans without current PTSD and (4) their non-combat-exposed co-twins.
  
  
  RESULTS
  There were no significant differences between groups in hippocampal asymmetry. There were no group differences in performance of an auditory oddball target detection task or in P300 amplitude. There was a significant positive correlation between P300 amplitude and the magnitude of hippocampal asymmetry in participants with PTSD.
  
  
  CONCLUSIONS
  These findings suggest that greater hippocampal asymmetry in PTSD is associated with a need to allocate more attentional resources when processing significant environmental stimuli.
authors.affiliation: Discipline of Psychiatry, School of Medicine, University of Adelaide, Adelaide, Australia.
authors.forename: Timothy
authors.initials: T
authors.lastname: Hall
authors.affiliation: Discipline of Psychiatry, School of Medicine, University of Adelaide, Adelaide, Australia.|Ramsay Health Care (SA) Mental Health Services, Adelaide, South Australia.|Northern Mental Health, Adelaide Metro Mental Health Directorate, Adelaide, South Australia.
authors.forename: Cherrie
authors.initials: C
authors.lastname: Galletly
authors.affiliation: Cognitive Neuroscience Laboratory and School of Psychology, Flinders University of South Australia, Adelaide, Australia.
authors.forename: C Richard
authors.initials: CR
authors.lastname: Clark
authors.affiliation: Veterans Affairs Medical Centre Research Service, Manchester, New Hampshire, England.|Harvard Medical School, Boston, USA.
authors.forename: Melinda
authors.initials: M
authors.lastname: Veltmeyer
authors.affiliation: Discipline of Psychiatry, School of Medicine, University of Adelaide, Adelaide, Australia.
authors.forename: Linda J
authors.initials: LJ
authors.lastname: Metzger
authors.affiliation: Veterans Affairs Medical Centre Research Service, Manchester, New Hampshire, England.
authors.forename: Mark W
authors.initials: MW
authors.lastname: Gilbertson
authors.affiliation: Massachusetts General Hospital and Harvard Medical School, Boston, USA.
authors.forename: Scott P
authors.initials: SP
authors.lastname: Orr
authors.affiliation: Massachusetts General Hospital and Harvard Medical School, Boston, USA.
authors.forename: Roger K
authors.initials: RK
authors.lastname: Pitman
authors.affiliation: The Centre of Military and Veterans' Health, Adelaide, Australia.
authors.forename: Alexander
authors.initials: A
authors.lastname: McFarlane