title: Reaction time, inhibition, working memory and 'delay aversion' performance: genetic influences and their interpretation.
abstract: BACKGROUND
  For candidate endophenotypes to be useful for psychiatric genetic research, they first of all need to show significant genetic influences. To address the relative lack of previous data, we set to investigate the extent of genetic and environmental influences on performance in a set of theoretically driven cognitive-experimental tasks in a large twin sample. We further aimed to illustrate how test-retest reliability of the measures affects the estimates.
  
  
  METHODS
  Four-hundred 7- to 9-year-old twin pairs were assessed individually on tasks measuring reaction time, inhibition, working memory and 'delay aversion' performance. Test-retest reliability data on some of the key measures were available from a previous study.
  
  
  RESULTS
  Several key measures of reaction time, inhibition and working-memory performance indicated a moderate degree of genetic influence. Combining data across theoretically related tasks increased the heritability estimates, as illustrated by the heritability estimates of 60% for mean reaction time and 50% for reaction-time variability. Psychometric properties (reliability or ceiling effects) had a substantial influence on the estimates for some measures.
  
  
  CONCLUSIONS
  The data support the usefulness of several of the variables for endophenotype studies that aim to link genes to cognitive and motivational processes. Importantly, the data also illustrate specific conditions under which the true extent of genetic influences may be underestimated and hence the usefulness for genetic mapping studies compromised, and suggest ways to address this.
authors.affiliation: MRC Social, Genetic and Developmental Psychiatry Centre, Institute of Psychiatry, King's College London, UK. j.kuntsi@iop.kcl.ac.uk
authors.forename: Jonna
authors.initials: J
authors.lastname: Kuntsi
authors.forename: Hannah
authors.initials: H
authors.lastname: Rogers
authors.forename: Greer
authors.initials: G
authors.lastname: Swinard
authors.forename: Norbert
authors.initials: N
authors.lastname: Börger
authors.forename: Jaap
authors.initials: J
authors.lastname: van der Meere
authors.forename: Fruhling
authors.initials: F
authors.lastname: Rijsdijk
authors.forename: Philip
authors.initials: P
authors.lastname: Asherson
mesh_terms: D002648:Child; D006801:Humans; D007206:Individuality; D007266:Inhibition, Psychological; D007360:Intelligence / Q000235:genetics; D008570:Memory, Short-Term; D009042:Motivation; D009483:Neuropsychological Tests / Q000706:statistics & numerical data*; D010641:Phenotype; D011594:Psychometrics / Q000706:statistics & numerical data; D011930:Reaction Time / Q000235:genetics*; D012055:Reinforcement Schedule; D012931:Social Environment; D014429:Twins, Dizygotic / Q000235:genetics* / Q000523:psychology; D014430:Twins, Monozygotic / Q000235:genetics* / Q000523:psychology; D014888:Wechsler Scales / Q000706:statistics & numerical data