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15. Reaction time changes in ADHD

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15. Reaction time changes in ADHD

In one study, reaction time to a stop signal, percentage of failed response inhibitions, and standard deviation of reaction time to “go” trial (SDRT) successfully discriminated ADHD sufferers from non-sufferers. Ex-Gaussian decomposition of the reaction time distribution showed that both greater tau and greater sigma affected the results for SDRT. Meanwhile, the traditional measures of inhibitory control were equivalent, if not better, predictors of ADHD status than the ex-Gaussian parameters.1

15.1. Reaction time variance increased in ADHD

ADHD is characterized by an increased variance of reaction time in reaction tests.23456 The increased reaction time variability is supposed to correlate especially with problems of sustained attention, which, however, is controversial. Apparently, reaction time variance is particularly high in the group of ADHD sufferers who make a particularly high number of commisson errors (false-positive errors). Increased cortisol responses to a stressor correlated with increased variance in response time. . Elevated cortisol stress responses are very common in the ADHD-I subtype and are atypical for the ADHD-HI subtype.7895101112
Further, a later and reduced slowing of reaction times after errors than in non-affected individuals was reported.613
Increased individual response variance is a sign of increased neural noise. MPH improves this.14 Neural noise is represented by arhythmic signals in the cortex, measurable as “1/f noise” in the EEG. Dopamine deficiency worsens the signal-to-noise ratio. ADHD is characterized by decreased dopamine levels in the PFC and striatum. Stimulants such as MPH raise dopamine levels there. Increasing dopamine levels to the optimal level improves the signal-to-noise ratio.
Increased reaction time and increased reaction time variability appear to correlate with high dopamine receptor availability (“empty receptors”), which is associated with decreased tonic dopamine levels.15

The symptom of increased reaction time variance also significantly distinguishes ADHD from other mental disorders such as

  • Fear
  • Distress disorders (physical stress disorders, PTSD)
  • Oppositional Defiant Behavior (ODD)
  • Conduct Disorder (CD)
  • Typical developmental disorders

We are currently testing a reaction test to explore whether reaction time variability can be used for AD(HHD) diagnosis. This is the start of the ADxS.org - ADHD reaction test.

15.2. Reaction time reduction in ADHD?

Several studies and reports indicate a shorter reaction time in ADHD.161718 96 According to Barkley, especially in SCT (Sluggish Cognitive Tempo) the reaction time is consistently reduced.
According to another study, the reaction times of ADHD sufferers and non-affected persons do not differ, but the care performance does.
Another study of ADHD sufferers found that, contrary to expectation, carriers of the DRD4-7R gene polymorphism, which is one of the main candidates for heightened sensitivity and ADHD, did not have worse reaction times than unaffected individuals, but carriers of other DRD4 polymorphisms did. Others reported aberrant audiovisual multisensory processing.17
One study found a correlation of prolonged reaction times with ADHD-I.19


  1. Galloway-Long, Huang-Pollock, Neely (2021): Ahead of the (ROC) Curve: A Statistical Approach to Utilizing Ex-Gaussian Parameters of Reaction Time in Diagnosing ADHD Across Three Developmental Periods. J Int Neuropsychol Soc. 2021 Sep 7:1-14. doi: 10.1017/S1355617721000990. PMID: 34488917. n = 550

  2. Salum, Sato, Manfro, Pan, Gadelha, do Rosário, Polanczyk, Castellanos, Sonuga-Barke, Rohde (2019): Reaction time variability and attention-deficit/hyperactivity disorder: is increased reaction time variability specific to attention-deficit/hyperactivity disorder? Testing predictions from the default-mode interference hypothesis. Atten Defic Hyperact Disord. 2019 Mar;11(1):47-58. doi: 10.1007/s12402-018-0257-x.

  3. Machida, Johnson (2019): Integration and segregation of the brain relate to stability of performance in children and adolescents with varied levels of inattention and impulsivity. Brain Connect. 2019 Aug 23. doi: 10.1089/brain.2019.0671.

  4. Gilbert, Huddleston, Wu, Pedapati, Horn, Hirabayashi, Crocetti, Wassermann, Mostofsky (2019): Motor cortex inhibition and modulation in children with ADHD. Neurology. 2019 Aug 6;93(6):e599-e610. doi: 10.1212/WNL.0000000000007899.

  5. Epstein, Erkanli, Conners, Klaric, Costello, Angold (2003): Relations between Continuous Performance Test performance measures and ADHD behaviors. J Abnorm Child Psychol. 2003 Oct;31(5):543-54.

  6. Liu, Hanna, Hanna, Rough, Arnold, Gehring (2020): Behavioral and Electrophysiological Correlates of Performance Monitoring and Development in Children and Adolescents with Attention-Deficit/Hyperactivity Disorder. Brain Sci. 2020 Feb 2;10(2):E79. doi: 10.3390/brainsci10020079. PMID: 32024242.

  7. Paucke, Stibbe, Huang, Strauss(2019): Differentiation of ADHD and Depression Based on Cognitive Performance. J Atten Disord. 2019 Aug 13:1087054719865780. doi: 10.1177/1087054719865780.

  8. Saito, Kaga, Nakagawa, Okubo, Kohashi, Omori, Fukuda, Inagaki (2019): Association of inattention with slow-spindle density in sleep EEG of children with attention deficit-hyperactivity disorder. Brain Dev. 2019 Oct;41(9):751-759. doi: 10.1016/j.braindev.2019.05.004.

  9. Vortrag Barkley (2014) an der Lynn University, Minute 19:40

  10. Machida, Murias, Johnson (2019): Electrophysiological Correlates of Response Time Variability During a Sustained Attention Task. Front Hum Neurosci. 2019 Oct 15;13:363. doi: 10.3389/fnhum.2019.00363. eCollection 2019.

  11. Johnson, Kelly, Bellgrove, Barry, Cox, Gill, Robertson (2019): Response variability in attention deficit hyperactivity disorder: evidence for neuropsychological heterogeneity. Neuropsychologia. 2007 Mar 2;45(4):630-8.

  12. Lee, Shin, Stein (2010): Increased cortisol after stress is associated with variability in response time in ADHD children. Yonsei Med J 51:206–211

  13. Keute, Stenner, Mueller, Zaehle, Krauel (2019): Error-Related Dynamics of Reaction Time and Frontal Midline Theta Activity in Attention Deficit Hyperactivity Disorder (ADHD) During a Subliminal Motor Priming Task. Front Hum Neurosci. 2019 Oct 29;13:381. doi: 10.3389/fnhum.2019.00381. eCollection 2019.

  14. Pertermann, Bluschke, Roessner, Beste (2019): The Modulation of Neural Noise Underlies the Effectiveness of Methylphenidate Treatment in Attention-Deficit/Hyperactivity Disorder. Biol Psychiatry Cogn Neurosci Neuroimaging. 2019 Aug;4(8):743-750. doi: 10.1016/j.bpsc.2019.03.011.

  15. Lou, Rosa, Pryds, Karrebaek, Lunding, Cumming, Gjedde (2004): ADHD: increased dopamine receptor availability linked to attention deficit and low neonatal cerebral blood flow. Dev Med Child Neurol. 2004 Mar;46(3):179-83. doi: 10.1017/s0012162204000313. PMID: 14995087. n = 6

  16. Roshani, Piri, Malek, Michel, Vafaee (2019): Comparison of cognitive flexibility, appropriate risk-taking and reaction time in individuals with and without adult ADHD. Psychiatry Res. 2019 Jul 25:112494. doi: 10.1016/j.psychres.2019.112494.

  17. McCracken, Murphy, Burkitt, Glazebrook, Yielder (2020): Audiovisual Multisensory Processing in Young Adults With Attention-Deficit/Hyperactivity Disorder. Multisens Res. 2020 Jan 2:1-25. doi: 10.1163/22134808-20191472. n = 22

  18. Havenstein (2014): Arbeitsgedächtnisleistung und emotionale Interferenzkontrolle bei Erwachsenen mit Aufmerksamkeitsdefizit-/Hyperativitätsstörung (ADHS); Dissertation, Seite 43, n = 80

  19. Ünsel-Bolat, Ercan, Bolat, Süren, Bacanlı, Yazıcı, Rohde (2019): Comparisons between sluggish cognitive tempo and ADHD-restrictive inattentive presentation phenotypes in a clinical ADHD sample. Atten Defic Hyperact Disord. 2019 Mar 25. doi: 10.1007/s12402-019-00301-y. n = 155