KUNTSI, J., Frazier-Wood, A. C., Banaschewski,,T., Gill, M., Miranda, A., Oades, R. D., Roeyers, H., Rothenberger, A., Steinhausen, H-C., van der Meere, J. J., Faraone, S. V., Asherson, P., Rijsdijk, F. V.,

2013 Genetic analysis of reaction time variability: room for improvement? Psychological Medicine, 43, 1323 - 1333 [view article]

doi: 10.1017/S0033291712002061 [Request a copy]

Introduction: Increased reaction time (RT) variability on cognitive tasks requiring a speeded response is characteristic of several psychiatric disorders. -- In ADHD, the association with RT is strong phenotypically and genetically. -- YET high RT variability is not a stable impairment but shows ADHD-sensitive improvement under certain conditions, as those with rewards. -- The state regulation theory proposed that the RT variability difference score, which captures change from baseline to a rewarded or fast condition, specifically measures "state regulation" -- In contrast, the interpretation of RT variability baseline (slow, unrewarded) scores is debated.

Methods: We aimed directly to investigate the degree of phenotypic and etiological overlap between RT variability baseline and RT variability difference scores ..... thus we conducted genetic model fitting analyses on go/no-go and fast task RT variability data, across task conditions manipulating rewards and event rate, from a population twin (n=1,314) and an ADHD and control sibling-pair (n=1,265) sample.

1 - Phenotypic and genetic / familial correlations were consistently high (0.72 - 0.98) between RT variability baseline and RT variability difference scores, across tasks, manipulations (incentives, fast) & samples.

2 - In contrast, correlations were low between RT variability in the manipulated condition (incentives, fast) and RT vriability difference scores.

3 - A comparison across the two different Go/no-go task RT variability difference scores (slow-fast & slow-incentive) showed high phenotypic and genetic / familial overlap (correlations of 0.75-0.83).


a) Our finding that RT variability difference scores measure largely the same etiological process as RT variability under baseline (slow, unrewarded) condition supports theories of ADHD that emphasize malleability of observed high RT variability.

b) Given the statistical shortcomings of difference scores, we recommend the use of RT variability baseline scores for most analyses, including genetic analyses.