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Intraindividual variability in inhibitory function in adults with ADHD--an ex-Gaussian approach.

Gmehlin D, Fuermaier AB, Walther S, Debelak R, Rentrop M, Westermann C, Sharma A, Tucha L, Koerts J, Tucha O, Weisbrod M, Aschenbrenner S - PLoS ONE (2014)

Bottom Line: We did not find higher numbers of commission errors in aADHD, while the number of omissions was significantly increased compared with controls.In contrast to increased mean RT, the distributional parameter mu did not document a significant slowing in aADHD.Moreover, we found a significant correlation between tau and the number of omission errors.

View Article: PubMed Central - PubMed

Affiliation: Department of Clinical Psychology and Neuropsychology, SRH Klinikum, Karlsbad-Langensteinbach, Germany.

ABSTRACT

Objective: Attention deficit disorder (ADHD) is commonly associated with inhibitory dysfunction contributing to typical behavioral symptoms like impulsivity or hyperactivity. However, some studies analyzing intraindividual variability (IIV) of reaction times in children with ADHD (cADHD) question a predominance of inhibitory deficits. IIV is a measure of the stability of information processing and provides evidence that longer reaction times (RT) in inhibitory tasks in cADHD are due to only a few prolonged responses which may indicate deficits in sustained attention rather than inhibitory dysfunction. We wanted to find out, whether a slowing in inhibitory functioning in adults with ADHD (aADHD) is due to isolated slow responses.

Methods: Computing classical RT measures (mean RT, SD), ex-Gaussian parameters of IIV (which allow a better separation of reaction time (mu), variability (sigma) and abnormally slow responses (tau) than classical measures) as well as errors of omission and commission, we examined response inhibition in a well-established GoNogo task in a sample of aADHD subjects without medication and healthy controls matched for age, gender and education.

Results: We did not find higher numbers of commission errors in aADHD, while the number of omissions was significantly increased compared with controls. In contrast to increased mean RT, the distributional parameter mu did not document a significant slowing in aADHD. However, subjects with aADHD were characterized by increased IIV throughout the entire RT distribution as indicated by the parameters sigma and tau as well as the SD of reaction time. Moreover, we found a significant correlation between tau and the number of omission errors.

Conclusions: Our findings question a primacy of inhibitory deficits in aADHD and provide evidence for attentional dysfunction. The present findings may have theoretical implications for etiological models of ADHD as well as more practical implications for neuropsychological testing in aADHD.

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Related in: MedlinePlus

Exemplary distribution of RT and relation of Mean, SD and the number of slow responses.NOTE: Dotted grey arrows illustrate a rightward shift of mean RT and an increase of the SD of RT as a consequence of an increasing number of slow responses forming the right tail of the distribution.
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pone-0112298-g001: Exemplary distribution of RT and relation of Mean, SD and the number of slow responses.NOTE: Dotted grey arrows illustrate a rightward shift of mean RT and an increase of the SD of RT as a consequence of an increasing number of slow responses forming the right tail of the distribution.

Mentions: Classical neuropsychological measures like the mean reaction time (mRT) and the standard deviation of reaction time (SD) as the most common and easy to compute variability measure are difficult to interpret because they are strongly correlated [18]. Consequently, mRT and SD do not distinguish between speed and variability. Moreover, as reaction times (RT) are not normally distributed, the mRT and SD may miss systematic aspects of the data due to averaging procedures. With regard to ADHD both behavioral and cognitive findings in children suggest that response patterns in patients are characterized by some overly slow responses falling within the right tail of the RT distribution [19] and therefore differ from control subjects. This pattern offers a possible explanation for both longer mean RT and increased SD without assuming a substantial general slowing of responses in ADHD (see Figure 1 below).


Intraindividual variability in inhibitory function in adults with ADHD--an ex-Gaussian approach.

Gmehlin D, Fuermaier AB, Walther S, Debelak R, Rentrop M, Westermann C, Sharma A, Tucha L, Koerts J, Tucha O, Weisbrod M, Aschenbrenner S - PLoS ONE (2014)

Exemplary distribution of RT and relation of Mean, SD and the number of slow responses.NOTE: Dotted grey arrows illustrate a rightward shift of mean RT and an increase of the SD of RT as a consequence of an increasing number of slow responses forming the right tail of the distribution.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4257533&req=5

pone-0112298-g001: Exemplary distribution of RT and relation of Mean, SD and the number of slow responses.NOTE: Dotted grey arrows illustrate a rightward shift of mean RT and an increase of the SD of RT as a consequence of an increasing number of slow responses forming the right tail of the distribution.
Mentions: Classical neuropsychological measures like the mean reaction time (mRT) and the standard deviation of reaction time (SD) as the most common and easy to compute variability measure are difficult to interpret because they are strongly correlated [18]. Consequently, mRT and SD do not distinguish between speed and variability. Moreover, as reaction times (RT) are not normally distributed, the mRT and SD may miss systematic aspects of the data due to averaging procedures. With regard to ADHD both behavioral and cognitive findings in children suggest that response patterns in patients are characterized by some overly slow responses falling within the right tail of the RT distribution [19] and therefore differ from control subjects. This pattern offers a possible explanation for both longer mean RT and increased SD without assuming a substantial general slowing of responses in ADHD (see Figure 1 below).

Bottom Line: We did not find higher numbers of commission errors in aADHD, while the number of omissions was significantly increased compared with controls.In contrast to increased mean RT, the distributional parameter mu did not document a significant slowing in aADHD.Moreover, we found a significant correlation between tau and the number of omission errors.

View Article: PubMed Central - PubMed

Affiliation: Department of Clinical Psychology and Neuropsychology, SRH Klinikum, Karlsbad-Langensteinbach, Germany.

ABSTRACT

Objective: Attention deficit disorder (ADHD) is commonly associated with inhibitory dysfunction contributing to typical behavioral symptoms like impulsivity or hyperactivity. However, some studies analyzing intraindividual variability (IIV) of reaction times in children with ADHD (cADHD) question a predominance of inhibitory deficits. IIV is a measure of the stability of information processing and provides evidence that longer reaction times (RT) in inhibitory tasks in cADHD are due to only a few prolonged responses which may indicate deficits in sustained attention rather than inhibitory dysfunction. We wanted to find out, whether a slowing in inhibitory functioning in adults with ADHD (aADHD) is due to isolated slow responses.

Methods: Computing classical RT measures (mean RT, SD), ex-Gaussian parameters of IIV (which allow a better separation of reaction time (mu), variability (sigma) and abnormally slow responses (tau) than classical measures) as well as errors of omission and commission, we examined response inhibition in a well-established GoNogo task in a sample of aADHD subjects without medication and healthy controls matched for age, gender and education.

Results: We did not find higher numbers of commission errors in aADHD, while the number of omissions was significantly increased compared with controls. In contrast to increased mean RT, the distributional parameter mu did not document a significant slowing in aADHD. However, subjects with aADHD were characterized by increased IIV throughout the entire RT distribution as indicated by the parameters sigma and tau as well as the SD of reaction time. Moreover, we found a significant correlation between tau and the number of omission errors.

Conclusions: Our findings question a primacy of inhibitory deficits in aADHD and provide evidence for attentional dysfunction. The present findings may have theoretical implications for etiological models of ADHD as well as more practical implications for neuropsychological testing in aADHD.

Show MeSH
Related in: MedlinePlus