Increased reaction time variability in attention-deficit hyperactivity disorder as a response-related phenomenon: evidence from single-trial event-related potentials.
BACKGROUND
Increased intra-subject variability (ISV) in reaction times (RTs) is a promising endophenotype for attention-deficit hyperactivity disorder (ADHD) and among the most robust hallmarks of the disorder. ISV has been assumed to represent an attentional deficit, either reflecting lapses in attention or increased neural noise. Here, we use an innovative single-trial event-related potential approach to assess whether the increased ISV associated with ADHD is indeed attributable to attention, or whether it is related to response-related processing.


METHODS
We measured electroencephalographic responses to working memory oddball tasks in patients with ADHD (N = 20, aged 11.3 ± 1.1) and healthy controls (N = 25, aged 11.7 ± 1.1), and analysed these data with a recently developed method of single-trial event-related potential analysis. Estimates of component latency variability were computed for the stimulus-locked and response-locked forms of the P3b and the lateralised readiness potential (LRP).


RESULTS
ADHD patients showed significantly increased ISV in behavioural ISV. This increased ISV was paralleled by an increase in variability in response-locked event-related potential latencies, while variability in stimulus-locked latencies was equivalent between groups. This result held across the P3b and LRP. Latency of all components predicted RTs on a single-trial basis, confirming that all were relevant for speed of processing.


CONCLUSIONS
These data suggest that the increased ISV found in ADHD could be associated with response-end, rather than stimulus-end processes, in contrast to prevailing conceptions about the endophenotype. This mental chronometric approach may also be useful for exploring whether the existing lack of specificity of ISV to particular psychiatric conditions can be improved upon.
Department of Child and Adolescent Psychiatry, Psychotherapy, and Psychosomatics, University of Freiburg, Freiburg, Germany.|School of Psychology, Bangor University, Bangor, UK.
Christopher W N
CWN
Saville
Department of Psychiatry and Psychotherapy, University of Freiburg, Freiburg, Germany.
Bernd
B
Feige
Department of Child and Adolescent Psychiatry, Psychotherapy, and Psychosomatics, University of Freiburg, Freiburg, Germany.
Christian
C
Kluckert
Department of Child and Adolescent Psychiatry, University of Frankfurt, Frankfurt, Germany.
Stephan
S
Bender
Department of Child and Adolescent Psychiatry, Psychotherapy, and Psychosomatics, University of Freiburg, Freiburg, Germany.
Monica
M
Biscaldi
Department of Psychology, Ben Gurion University of the Negev, Negev, Israel.
Andrea
A
Berger
Department of Child and Adolescent Psychiatry, Psychotherapy, and Psychosomatics, University of Freiburg, Freiburg, Germany.
Christian
C
Fleischhaker
Department of Child and Adolescent Psychiatry, Psychotherapy, and Psychosomatics, University of Freiburg, Freiburg, Germany.
Klaus
K
Henighausen
Department of Child and Adolescent Psychiatry, Psychotherapy, and Psychosomatics, University of Freiburg, Freiburg, Germany.|School of Psychology, Bangor University, Bangor, UK.
Christoph
C
Klein
D001288:Attention / Q000502:physiology; D001289:Attention Deficit Disorder with Hyperactivity / Q000175:diagnosis* / Q000503:physiopathology*; D002540:Cerebral Cortex / Q000503:physiopathology; D002648:Child; D003265:Contingent Negative Variation / Q000502:physiology*; D003657:Decision Making; D004292:Dominance, Cerebral / Q000502:physiology; D004569:Electroencephalography; D058068:Endophenotypes; D018913:Event-Related Potentials, P300 / Q000502:physiology*; D006801:Humans; D008297:Male; D008570:Memory, Short-Term / Q000502:physiology*; D011930:Reaction Time / Q000502:physiology*; D012016:Reference Values
ADHD; EEG; event-related potential; reaction time; working memory