Neuropsychological characteristics of adults with attention‐deficit/hyperactivity disorder without intellectual disability

Abstract Aims While several studies have reported various cognitive impairments in children with attention‐deficit/hyperactivity disorder, the neuropsychological profiles of adults with this disorder are understudied. Here, the intelligence and memory functions of adults with attention‐deficit/hyperactivity disorder without intellectual disability were evaluated. Methods The Wechsler Adult Intelligence Scale—Third Edition and Wechsler Memory Scale—Revised were administered to 30 adults with attention‐deficit/hyperactivity disorder whose full‐scale intelligence quotients were >85. Diagnoses were based on the Diagnostic and Statistical Manual of Mental Disorders‐IV criteria. Conners' Adult ADHD Rating Scales—Self‐Report—screening version and the Autism Spectrum Quotient were also evaluated. Results In the Wechsler Adult Intelligence Scale—Third Edition, the verbal intelligence quotient was significantly higher than the performance intelligence quotient and the verbal comprehension score was the highest among the secondary indices. In the Wechsler Memory Scale—Revised, the visual memory score was the highest measure. Although the verbal intelligence quotient had no correlation with any Wechsler Memory Scale—Revised measures, the performance intelligence quotient was significantly correlated with the visual memory and attention scores of the Wechsler Memory Scale—Revised. Conners' Adult ADHD Rating Scales hyperactive‐impulsive score was significantly correlated with the verbal intelligence quotient, whereas the inattention score was not correlated with any measures of the Wechsler Adult Intelligence Scale—Third Edition or Wechsler Memory Scale—Revised. Conclusions The results suggest that while adults with normal‐intelligence attention‐deficit/hyperactivity disorder have comparatively high verbal comprehension and social knowledge, their ability of information processing and visual‐motor coordination are relatively weak.

ity (full-scale IQ < 85) or with severe physical disorders, any other psychiatric disorder, or substance abuse or dependence were excluded. The Japanese version of Conners' Adult ADHD Rating Scales (CAARS)-Self-Report-screening version (CAARS-SR-SV) and Japanese version of the Autism Spectrum Quotient (AQ) were also assessed 8,9,10 in order to evaluate the participants' subjective symptoms. The participants' ages ranged from 18 to 59 with a mean of 31.4 years (standard deviation; SD: 10.8), and the average duration of education was 14.3 years (SD: 1.9; ranged from 12 to 18 years).
The CAARS average inattentive (IA) subscale score was 18.2 (SD: 6.1; ranged from 6 to 27) and the hyperactive/impulsive (HI) subscale score was 9.1 (SD: 6.2; ranged from 1 to 23), which were higher than those in healthy adults. 8 The average AQ score was 31.5 (SD: 6.5; ranged from 15 to 41), which was also higher than that of the healthy adults, although it was lower than the cutoff of 33 points for autism spectrum disorder (ASD). 10 SPSS 22.0J (IBM Corp.) was used for all statistical analyses. The means with standard deviations were calculated for the WAIS-III, WMS-R, AQ, and CAARS. The paired t test was used to calculate the VIQ-PIQ difference of the WAIS-III. One-way repeated-measures analysis of variance was used to compare the secondary indices of the WAIS-III and each measurement of the WMS-R; post hoc pairwise comparisons were performed with Bonferroni correction.
Pearson's product-moment correlation coefficients were calculated among the measurements of the WAIS-III and WMS-R as well as among the measurements of clinical symptoms and the WAIS-III and WMS-R. The significance level was set at 0.05, except for the correlations, at which 0.01 was set to count for the possible type I error. normal range. VIQ was significantly higher than PIQ (t(29) = 2.855, P < .01). Concerning the secondary indices, significant within-participants effects were found (F(2.42) = 4.723, P < .01, ηp 2 = 0.14) with post hoc pairwise comparisons, revealing that the score of verbal comprehension (VC) was significantly higher than that of working memory (WM; P < .05). All measurements of the WMS-R were also within the normal range. The within-participants effects were also significant (F(2.21) = 6.654, P < .01, ηp 2 = 0.187) with the pairwise comparison resulting in the score of visual memory being significantly higher than that of verbal memory (P < .01), general memory (P < .01), and delayed memory (P < .05).

| RE SULTS
Pearson's product-moment correlation coefficients were calculated between the IQ values of the WAIS-III and WMS-R ( Table 2).   The finding of higher VIQ compared to PIQ in this study may be associated with the relatively high AQ score in the participants compared with neurotypicals 10 , although none were diagnosed with ASD. With several studies reporting higher VIQ in individuals with ASD, 11 Several limitations of our study must be considered. First, only 30 participants were included, limiting the statistical power of the study. Second, we did not include normal controls as comparison.

| D ISCUSS I ON
Third, possible effects of medication were not considered. At the time of our assessment, 10 of the 30 participants were on either methylphenidate or atomoxetine. Fourth, only subjective measurements of self-rating scales were used to assess symptoms, lacking objective clinician rating scales.
This study highlights the uneven intelligence and memory profiles of adults with ADHD with possible relation to symptoms.
Further studies that determine the association of daily functioning and medication regimens with objective measures of symptoms are to be planned.

ACK N OWLED G M ENTS
We thank the doctors of the Department of Psychiatry at Showa University for their helpful advice and support in the present study. We would also like to thank Editage for English language editing.

CO N FLI C T O F I NTE R E S T
The authors declare no conflict of interest.

AUTH O R CO NTR I B UTI O N S
MH was critically involved in the analysis of the data and wrote the first draft of the manuscript. WH contributed to the interpretation of the data and the writing of the manuscript. AI was critically involved in the study design and analysis of the data and contributed to the interpretation of the data and the writing of the manuscript.
YO and OT were involved in the subject recruitment process and the clinical diagnostic assessments. All authors contributed to and approved the final manuscript.

A PPROVA L O F TH E R E S E A RCH PROTO CO L BY A N I N S TITUTI O N A L R E V I E WER B OA R D
The study protocol has been approved by the suitably consti-

I N FO R M E D CO N S E NT
All participants provided written consent to the study after a full explanation of the study procedures.

DATA AVA I L A B I L I T Y S TAT E M E N T
Research data are not shared. This is because the participants did not consent for open data sharing.