title: Modifiable Arousal in Attention-Deficit/Hyperactivity Disorder and Its Etiological Association With Fluctuating Reaction Times.
abstract: BACKGROUND
  Cognitive theories of attention-deficit/hyperactivity disorder (ADHD) propose that high within-subject fluctuations of cognitive performance in ADHD, particularly reaction time (RT) variability (RTV), may reflect arousal dysregulation. However, direct evidence of arousal dysregulation and how it may account for fluctuating RTs in ADHD is limited. We used skin conductance (SC) as a measure of peripheral arousal and aimed to investigate its phenotypic and familial association with RTV in a large sample of ADHD and control sibling pairs.
  
  
  METHODS
  Adolescents and young adults (N= 292), consisting of 73 participants with ADHD and their 75 siblings, and 72 controls and their 72 siblings, completed the baseline (slow, unrewarded) and fast-incentive conditions of a RT task, while SC was simultaneously recorded.
  
  
  RESULTS
  A significant group-by-condition interaction emerged for SC level (SCL). Participants with ADHD had decreased SCL, compared with controls, in the baseline condition but not the fast-incentive condition. Baseline SCL was negatively associated with RTV, and multivariate model fitting demonstrated that the covariance of SCL with RTV, and of SCL with ADHD, was mostly explained by shared familial effects.
  
  
  CONCLUSIONS
  ADHD is associated with decreased, but modifiable, tonic peripheral arousal. A shared familial cause underlies the relationship between arousal and RTV and between arousal and ADHD. Given the malleability of SCL, if our findings are replicated, it warrants further exploration as a potential treatment target for ADHD.
authors.affiliation: MRC Social, Genetic and Developmental Psychiatry Centre, Institute of Psychiatry, Psychology and Neuroscience, King's College London, London. Electronic address: sarah.2.james@kcl.ac.uk.
authors.forename: Sarah-Naomi
authors.initials: SN
authors.lastname: James
authors.affiliation: Department of Psychology, Institute of Psychiatry, Psychology and Neuroscience, King's College London, London; Centre for Brain and Cognitive Development (CHMC), Department of Psychological Sciences, Birkbeck, University of London, London, United Kingdom.
authors.forename: Celeste H M
authors.initials: CHM
authors.lastname: Cheung
authors.affiliation: MRC Social, Genetic and Developmental Psychiatry Centre, Institute of Psychiatry, Psychology and Neuroscience, King's College London, London.
authors.forename: Fruhling
authors.initials: F
authors.lastname: Rijsdijk
authors.affiliation: MRC Social, Genetic and Developmental Psychiatry Centre, Institute of Psychiatry, Psychology and Neuroscience, King's College London, London.
authors.forename: Philip
authors.initials: P
authors.lastname: Asherson
authors.affiliation: MRC Social, Genetic and Developmental Psychiatry Centre, Institute of Psychiatry, Psychology and Neuroscience, King's College London, London.
authors.forename: Jonna
authors.initials: J
authors.lastname: Kuntsi
keywords: ADHD; Arousal; Familial influences; Reaction time variability; Sibling study; Skin conductance