title: Enhanced neurocognitive functioning and positive temperament in twins discordant for bipolar disorder.
abstract: OBJECTIVE
  Based on evidence linking creativity and bipolar disorder, a model has been proposed whereby factors influencing liability to bipolar disorder confer certain traits with positive effects on reproductive fitness. The authors tested this model by examining key traits known to be associated with evolutionary fitness, namely, temperament and neurocognition, in individuals carrying liability for bipolar disorder. Schizophrenia probands and their co-twins were included as psychiatric controls.
  
  
  METHODS
  Twin pairs discordant for bipolar disorder and schizophrenia and control pairs were identified through the Swedish Twin Registry. The authors administered a neuropsychological test battery and temperament questionnaires to samples of bipolar probands, bipolar co-twins, schizophrenia probands, schizophrenia co-twins, and controls. Multivariate mixed-model analyses of variance were conducted to compare groups on temperament and neurocognitive scores.
  
  
  RESULTS
  Bipolar co-twins showed elevated scores on a "positivity" temperament scale compared with controls and bipolar probands, while bipolar probands scored higher on a "negativity" scale compared with their co-twins and controls, who did not differ. Additionally, bipolar co-twins showed superior performance compared with controls on tests of verbal learning and fluency, while bipolar probands showed performance decrements across all neurocognitive domains. In contrast, schizophrenia co-twins showed attenuated impairments in positivity and overall neurocognitive functioning relative to their ill proband counterparts.
  
  
  CONCLUSIONS
  These findings suggest that supra-normal levels of sociability and verbal functioning may be associated with liability for bipolar disorder. These effects were specific to liability for bipolar disorder and did not apply to schizophrenia. Such benefits may provide a partial explanation for the persistence of bipolar illness in the population.
authors.affiliation: From the Department of Psychology, University of California, Los Angeles; the Department of Medical Epidemiology and Biostatistics, Karolinska Institute, Stockholm; and the Department of Psychology, Yale University, New Haven, Conn.
authors.forename: Rachel G
authors.initials: RG
authors.lastname: Higier
authors.forename: Amy M
authors.initials: AM
authors.lastname: Jimenez
authors.forename: Christina M
authors.initials: CM
authors.lastname: Hultman
authors.forename: Jacqueline
authors.initials: J
authors.lastname: Borg
authors.forename: Cristina
authors.initials: C
authors.lastname: Roman
authors.forename: Isabelle
authors.initials: I
authors.lastname: Kizling
authors.forename: Henrik
authors.initials: H
authors.lastname: Larsson
authors.forename: Tyrone D
authors.initials: TD
authors.lastname: Cannon
mesh_terms: D000328:Adult; D001714:Bipolar Disorder / Q000453:epidemiology / Q000523:psychology*; D003071:Cognition; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009483:Neuropsychological Tests; D012042:Registries; D012559:Schizophrenia / Q000453:epidemiology; D012565:Schizophrenic Psychology; D066107:Social Skills; D013548:Sweden / Q000453:epidemiology; D013694:Temperament; D014427:Twins; D014706:Verbal Learning