title: Reduced hippocampal volume is associated with overgeneralization of negative context in individuals with PTSD.
abstract: OBJECTIVE
  Previous studies demonstrated reduced hippocampal volume in individuals with posttraumatic stress disorder (PTSD). However, the functional role the hippocampus plays in PTSD symptomatology is still unclear. The aim of the present study was to explore generalization learning and its connection to hippocampal volume in individuals with and without PTSD. Animal and human models argue that hippocampal deficit may result in failure to process contextual information. Therefore we predicted associations between reduced hippocampal volume and overgeneralization of context in individuals with PTSD.
  
  
  METHODS
  We conducted MRI scans of bilateral hippocampal and amygdala formations as well as intracranial and total brain volumes. Generalization was measured using a novel-learning paradigm, which separately evaluates generalization of cue and context in conditions of negative and positive outcomes.
  
  
  RESULTS
  As expected, MRI scans indicated reduced hippocampal volume in PTSD compared to non-PTSD participants. Behavioral results revealed a selective deficit in context generalization learning in individuals with PTSD, F(1, 43) = 8.27, p < .01, η(p)² = .16. Specifically, as predicted, while generalization of cue was spared in both groups, individuals with PTSD showed overgeneralization of negative context. Hence, they could not learn that a previously negative context is later associated with a positive outcome, F(1, 43) = 7.33, p = .01, η(p)² = .15. Most importantly, overgeneralization of negative context significantly correlated with right and left hippocampal volume (r = .61, p = .000; r = .5, p = .000). Finally, bilateral hippocampal volume provided the strongest prediction of overgeneralization of negative context.
  
  
  CONCLUSIONS
  Reduced hippocampal volume may account for the difficulty of individuals with PTSD to differentiate negative and novel conditions and hence may facilitate reexperiencing symptoms.
authors: Institute for the Study of Affective Neuroscience, University of Haifa.
authors: Einat
authors: E
authors: Levy-Gigi
authors: National Institute of Psychiatry and Addictions, Nyírö Gyula Hospital.
authors: Csilla
authors: C
authors: Szabo
authors: Institute for the Study of Affective Neuroscience, Department of Psychology, University of Haifa.
authors: Gal
authors: G
authors: Richter-Levin
authors: National Institute of Psychiatry and Addictions, Nyírö Gyula Hospital, Department of Physiology, Faculty of Medicine, University of Szeged.
authors: Szabolcs
authors: S
authors: Kéri
mesh_terms: D000328:Adult; D000679:Amygdala / Q000473:pathology* / Q000503:physiopathology; D001921:Brain / Q000473:pathology; D005260:Female; D006624:Hippocampus / Q000473:pathology* / Q000503:physiopathology; D006801:Humans; D007858:Learning; D008279:Magnetic Resonance Imaging; D008297:Male; D009929:Organ Size; D013313:Stress Disorders, Post-Traumatic / Q000473:pathology* / Q000503:physiopathology