title: The genetic and environmental influences of event-related gamma oscillations on bipolar disorder.
abstract: OBJECTIVE
  Gamma oscillations have been proposed to play an important role in neural information coding. There have been a limited number of electrophysiology studies in evoked gamma band responses (GBRs) in bipolar disorder (BPD). It is also unclear whether GBR deficits, if present, are potential endophenotypes for BPD as little is known about the heritability of GBRs. The present study aimed to examine whether GBRs derived from two auditory tasks, the oddball task and the dual-click paradigm, are potential BPD endophenotypes.
  
  
  METHODS
  A total of 308 subjects were included in this study: 198 healthy controls, 59 BPD patients (22 monozygotic BPD twins and 37 BPD patients from 31 families), and 51 unaffected relatives. The evoked gamma responses were calculated using a Morlet wavelet transformation. Structural equation modelling was applied to obtain the genetic (heritability) and environment estimates in each GBR variable and their (genetic) overlap with BPD.
  
  
  RESULTS
  The heritability estimates of GBR to standard stimuli were 0.51 and 0.35 to target stimuli in the oddball task. However, neither response type was impaired in BPD patients or their unaffected relatives. The heritability estimates of GBR to S1 stimuli were 0.54 and 0.50 to S2 stimuli in the dual-click paradigm. BPD patients had reduced gamma power and suppression to S1 stimuli but their unaffected relatives did not.
  
  
  CONCLUSIONS
  Evoked GBRs are heritable traits. However, GBR deficits are not observed in clinically unaffected relatives nor associated with BPD. Gamma responses do not appear to satisfy criteria for being BPD endophenotypes.
authors.affiliation: Psychology Research Laboratory, Harvard Medical School, McLean Hospital Research Service, Boston, MA, USA. mhall@mclean.harvard.edu
authors.forename: Mei-Hua
authors.initials: MH
authors.lastname: Hall
authors.forename: Kevin M
authors.initials: KM
authors.lastname: Spencer
authors.forename: Katja
authors.initials: K
authors.lastname: Schulze
authors.forename: Colm
authors.initials: C
authors.lastname: McDonald
authors.forename: Sridevi
authors.initials: S
authors.lastname: Kalidindi
authors.forename: Eugenia
authors.initials: E
authors.lastname: Kravariti
authors.forename: Fergus
authors.initials: F
authors.lastname: Kane
authors.forename: Robin M
authors.initials: RM
authors.lastname: Murray
authors.forename: Elvira
authors.initials: E
authors.lastname: Bramon
authors.forename: Pak
authors.initials: P
authors.lastname: Sham
authors.forename: Frühling
authors.initials: F
authors.lastname: Rijsdijk
mesh_terms: D000161:Acoustic Stimulation / Q000379:methods; D000293:Adolescent; D000328:Adult; D001714:Bipolar Disorder / Q000235:genetics* / Q000503:physiopathology*; D001931:Brain Mapping; D004192:Discrimination, Psychological; D004200:Diseases in Twins; D004569:Electroencephalography / Q000379:methods; D004777:Environment; D005072:Evoked Potentials, Auditory / Q000235:genetics* / Q000502:physiology; D005190:Family; D005192:Family Health; D005260:Female; D006801:Humans; D016014:Linear Models; D008297:Male; D008875:Middle Aged; D009483:Neuropsychological Tests; D014429:Twins, Dizygotic / Q000235:genetics; D014430:Twins, Monozygotic / Q000235:genetics; D055815:Young Adult