15. Time and reaction time in ADHD

Author: Ulrich Brennecke
Review: Dipl.-Psych. Waldemar Zdero

Reaction time variability in the Continuous Performance Test (CPT), the analog of the 5-CSRTT for humans, is the most frequently observed deficit in neurodevelopmental disorders.¹

An altered perception of time is often reported in ADHD.
In addition, ADHD is characterized by an increased reaction time variance in reaction tests. The increased reaction time variance clearly distinguishes ADHD from other mental disorders such as anxiety, PTSD, ODD, CD and typical developmental disorders.
A slower reaction time and a larger standard deviation of the reaction time may be due to a lower decoding accuracy of the brain. Reaction time variance is particularly high in persons with ADHD who make many commission errors (confusion errors, false-positive errors). In addition, increased cortisol secretion correlates with an increased variance in response time.
ADHD shows a later and less pronounced slowing of reaction time after errors compared to non-affected individuals. An increased reaction time and reaction time variance also appear to correlate with a high availability of dopamine receptors, which is associated with a reduced dopamine level.

There is evidence of shorter reaction time in ADHD, and even more so in SCT. In one study, reaction time to a stop signal, the percentage of failed response inhibitions, and the standard deviation of reaction time to the “go” trial (SDRT) successfully differentiated people with ADHD from those without. Ex-Gaussian decomposition of the reaction time distribution showed that both a larger tau and a larger sigma affected the results for the SDRT.² Meanwhile, the traditional measures of inhibitory control were equally if not better predictors of ADHD status than the ex-Gaussian parameters.³

• 15.1. Reaction time variance increased in ADHD
• 15.2. Reduced reaction time in ADHD?
• 15.3. Rhythm problems
• 15.4. Changed perception of time

15.1. Reaction time variance increased in ADHD¶

ADHD is characterized by an increased variance in reaction time in response tests ^{4 5 6 7 89}
The increased reaction time variability is thought to correlate particularly with problems of sustained attention,^{1011 12} but this is controversial.⁷¹³ Slower reaction time and greater standard deviation of reaction time also appear to be the consequences of lower parieto-occipital multivariate decoding accuracy, which occurred around 240-340 ms after the onset of visual search.¹⁴
Apparently, the response time variance is particularly high in the group of people with ADHD who make a particularly large number of commission errors (confusion errors, false-positive errors).¹⁵ Increased cortisol responses to a stressor correlated with an increased variance in response time.¹⁶ Elevated cortisol stress responses are very common in the ADHD-I subtype and atypical for the ADHD-HI subtype.
Furthermore, a later and reduced slowdown in reaction times after errors was reported than in those not affected.⁸¹⁷
Increased individual response variance is a sign of increased neural noise. MPH improves this.¹⁸ Neural noise is represented by arrhythmic signals in the cortex, which can be measured as “1/f noise” in the EEG. Dopamine deficiency worsens the signal-to-noise ratio. ADHD is characterized by reduced dopamine levels in the PFC and striatum. Stimulants such as MPH increase the dopamine level there. An increase in dopamine levels to the optimal level improves the signal-to-noise ratio.
Increased reaction time and increased reaction time variability seem to correlate with a high availability of dopamine receptors (“empty receptors”), which is associated with reduced tonic dopamine levels.¹⁹

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

• Fear
• Distress disorders (physical stress disorders, PTSD)
• Oppositional defiant behavior (ODD)
• Disorder of social behavior (Conduct Disorder, CD)
• Typical developmental disorders

We are currently testing a reaction test to explore whether reaction time variability can be used to diagnose ADHD. This is where the ADxS.org - ADHD reaction test starts.

15.2. Reduced reaction time in ADHD?¶

Several studies and reports indicate a shorter reaction time in ADHD.^{202122 128} According to Barkley, the reaction time is consistently reduced, especially with SCT (sluggish cognitive tempo)
According to another study, the reaction times of people with ADHD do not differ from those without ADHD, but the level of care does.
Contrary to all expectations, people with ADHD who carried the DRD4-7R gene polymorphism, which is one of the main candidates for increased sensitivity and ADHD, did not show poorer reaction times than non-affected people. However, carriers of other DRD4 polymorphisms did. Others reported deviating audiovisual multisensory processing.²¹
One study found a correlation of prolonged reaction times with ADHD-I.²³

15.3. Rhythm problems¶

A study reports that people with ADHD have significantly more problems tapping out a given rhythm with their fingers.²⁴ The test targets the function of the cerebellum, which is one of the brain regions involved in ADHD.
The difficulties correlated with the degree of hyperactivity/impulsivity. Higher impulsivity correlated with a faster tapping frequency,²⁵

15.4. Changed perception of time¶

The perception of time is altered in ADHD.
This concerns the perception of different lengths of time, although perception for these different time windows is carried out by different regions of the brain.²⁶

While time in the world around us has a uniform speed, the perception of this speed varies from person to person²⁷
In ADHD, there are deficits in reproducing and estimating fixed durations. Children with ADHD tend to state the interval of a certain period of time longer than it was when estimating it, while they keep it too short when they are supposed to reproduce it.²⁸²⁹ People with ADHD therefore have a consistently deviating internal clock. The speed of cognitive functions based on temporal processing is increased. As a result, time passes subjectively faster for people with ADHD than for those not affected, so that real time is perceived as “sluggish”. According to the authors, this disorder in the subjective perception of time should explain the increased avoidance of delays, the stronger perception of boredom, the unpleasant perception of waiting times and the devaluation of distant rewards.
We consider this to be a misinterpretation. If time passes subjectively faster, a distant reward should become relatively more valuable compared to those who are not affected, as the reward subjectively occurs earlier. The correlation is nevertheless undisputed, we merely doubt the causality.

One hypothesis explains impulsivity symptoms of ADHD in particular with inter-individual differences in the perception of time of people with ADHD.³⁰²⁶ The time estimation of children with ADHD was even worse if they had particularly high impulsivity.³¹

One study found evidence that hyperactivity could be due less to reduced impulse inhibition than to an altered perception of time.³²

A faster subjective time in ADHD was interpreted as an additional factor for a devaluation of distant rewards.²⁶ However, this seems questionable to us, because if an objective period of time is subjectively perceived faster, this should be accompanied by a subjectively shorter perceived time, which should tend to counteract a devaluation of distant rewards.
However, there appears to be a more direct link between the devaluation of more distant rewards and impulsivity: subjective time perception can be experimentally assessed using hyperbolic delay discounting procedures to model the influence of time perception on decision making. Hyperbolic delay discounting describes the tendency (known from ADHD) to prefer smaller immediate rewards over larger but delayed rewards.²⁶ This method thus assumes a direct link between the devaluation of more distant rewards and impulsivity.
Addiction research also reports a correlation between impulsivity and a devaluation of more distant rewards, which is attributed to an altered perception of time.³³

In a video game in which rewards were temporally decoupled from the action, people with ADHD performed as well as non-affected people in terms of executive function.³⁵ One study reports that self-perception of attention difficulties in ADHD (and ASD) does not correlate with actual performance in attention tests.³⁶

The perception of time is regulated in the brain by a complex network of timers, accumulators and comparison elements. The hippocampus and the entorhinal cortex are responsible for the longer measures of time and the cerebellum for the measures of time of fractions of a second, which are required in particular for brain-muscle coordination.³⁷