title: Different genetic factors underlie fear conditioning and episodic memory.
abstract: OBJECTIVE
  Fear conditioning seems to account for the acquisition of post-traumatic stress disorder, whereas conscious recall of events in aftermath of trauma reflects episodic memory. Studies show that both fear conditioning and episodic memory are heritable, but no study has evaluated whether they reflect common or separate genetic factors. To this end, we studied episodic memory and fear conditioning in 173 healthy twin pairs using visual stimuli predicting unconditioned electric shocks.
  
  
  METHODS
  Fear conditioning acquisition and extinction was determined using conditioned visual stimuli predicting unconditioned mild electric shocks, whereas electrodermal activity served as the fear learning index. Episodic memory was evaluated using cued recall of pictorial stimuli unrelated to conditioning. We used multivariate structural equation modeling to jointly analyze memory performance and acquisition as well as extinction of fear conditioning.
  
  
  RESULTS
  Best-fit twin models estimated moderate genetic loadings for conditioning and memory measures, with no genetic covariation between them.
  
  
  CONCLUSIONS
  Individual differences in fear conditioning and episodic memory reflect distinct genetically influenced processes, suggesting that the genetic risk for learning-induced anxiety disorders includes at least two memory-related genetic factors. These findings are consistent with the facts that the two separate learning forms are distant in their evolutionary development, involve different brain mechanisms, and support that genetically independent memory systems are pivotal in the development and maintenance of syndromes related to fear learning.
authors.affiliation: aDepartment of Psychology, Uppsala University, Uppsala bDepartment of Clinical Neuroscience, Karolinska Institutet, Stockholm, Sweden cDepartment of Psychiatry, Virginia Institute for Psychiatry and Behavioral Genetics, Virginia Commonwealth University, Richmond, Virginia, USA.
authors.forename: Mats
authors.initials: M
authors.lastname: Fredrikson
authors.forename: Peter
authors.initials: P
authors.lastname: Annas
authors.forename: John M
authors.initials: JM
authors.lastname: Hettema
mesh_terms: D000328:Adult; D003214:Conditioning, Classical / Q000502:physiology*; D004558:Electric Stimulation; D005239:Fear / Q000502:physiology* / Q000523:psychology*; D005260:Female; D006801:Humans; D008297:Male; D061212:Memory, Episodic; D008960:Models, Psychological; D015999:Multivariate Analysis; D010775:Photic Stimulation / Q000379:methods; D013313:Stress Disorders, Post-Traumatic / Q000235:genetics* / Q000523:psychology*; D014427:Twins / Q000235:genetics* / Q000523:psychology