ARTICLE
Neuropsychological Executive Functions and DSM-IV ADHD Subtypes

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ABSTRACT

Objective

To evaluate and compare a focused set of component neuropsychological executive functions in the DSM-IV attention-deficit/hyperactivity disorder combined (ADHD-C) and inattentive (ADHD-I) subtypes.

Method

The Stop task, Tower of London, Stroop task, Trailmaking Test, and output speed measures were completed by 105 boys and girls aged 7–12 classified as either DSM-IV ADHD-C (n = 46), ADHD-I (n = 18), or community control (n = 41).

Results

Both subtypes had deficits on output speed. A group × gender interaction was observed on the Stop task: boys with ADHD-C were impaired versus boys with ADHD-I, whereas girls in the two subtypes did not differ. The ADHD-C type had a deficit in planning. Neither ADHD group had a deficit in interference control per se, although they were slower than controls on the Stroop tasks.

Conclusions

ADHD-I shares neuropsychological deficits with ADHD-C in the domain of output speed; on most domains the subtypes did not differ. Neuropsychological distinctions between these ADHD subtypes may be few, depending on which domain of executive functioning is assessed, and these distinctions differ by gender. In the case of boys, the two subtypes may be distinguished by the specificity of motor inhibition deficits to ADHD-C.

Section snippets

Summary

The goal of the present study was to examine the DSM-IV combined and inattentive subtypes on a focused, rational battery of selected, commonly used executive function measures. We considered that the inattentive and combined subtypes might reflect related but distinct syndromes. For the combined type, we expected to replicate prior findings that describe deficits in motor inhibition (assessed by a computerized Stop Signal task) and in planning (assessed by the Tower of London task). For the

Participants

A total of 105 children participated in three groups: ADHD combined type (ADHD-C, n = 46), ADHD inattentive type (ADHD-I, n = 18), and non-ADHD controls (n = 41). Child participants from first through sixth grade were recruited from a local pediatric clinic specializing in ADHD referrals, from a local support group for parents of children with ADHD, and from invitation letters sent to parents of children in the local school districts. To the extent possible, control children were matched on

Sample Description

Sample descriptive characteristics are summarized in Table 1. As shown, groups did not differ in age or gender composition.

There was a tendency for more ethnic minority representation in the control group. The ADHD-C and ADHD-I groups did not differ on IQ, but the ADHD-C group had a lower IQ than the control group. As expected, the ADHD-C group had a greater ratio of conduct and oppositional defiant disorders than the other two groups, RD was more common in the ADHD-I than in the control group,

DISCUSSION

This study investigated two ADHD subtypes on four operational domains of executive functioning and on output speed. Overall, the findings are consistent with the literature, but they also introduce new considerations for clarifying the relation of the two ADHD subtypes. The two ADHD groups had similar deficits compared with controls on key response speed measures, such as speed of the Go response (Stop task) and naming speed on the Stroop subtests, suggesting shared deficits in effort or

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    This work was supported by NIMH grant R03-MH57244. The Lansing and East Lansing School Districts provided valuable assistance.

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