The relationship between executive function, processing speed, and attention-deficit hyperactivity disorder in middle childhood

Abstract

Attention-Deficit Hyperactivity Disorder (ADHD) is a heterogeneous disorder that is highly impairing. Early, accurate diagnosis maximizes long-term positive outcomes for youth with ADHD. Tests of executive functioning (EF) are potential tools for screening and differential diagnosis of ADHD subtypes. However, previous research has been inconsistent regarding the specificity and magnitude of EF deficits across ADHD subtypes. Here, we advance knowledge of the EF-ADHD relationship by using: (1) dimensional latent factor models of ADHD that captures the heterogeneity of expression, and (2) a comprehensive, reliable battery of EF tasks and modeling relationships with a general factor of EF ability. We tested 1548 children and adolescents (ages 7-15 years) from the Texas Twin Project, a population-based cohort with a diverse socioeconomic and ethnic composition. We show that EF deficits were specific to the inattention domain of ADHD. Moreover, we found that the association between EF task performance and inattention was stable across sociodemographic groups. Our results demonstrate that failures of executive control are selectively manifested as covert inattentive symptoms, such as trouble with organization, forgetfulness, and distractedness, rather than overt symptoms, such as inappropriate talkativeness and interruption. Future research, utilizing a bifactor characterization of ADHD in clinical samples, is needed to further refine understanding of the nature of cognitive deficits in ADHD across the full range of symptom variation.

Keywords: ADHD; executive function; hyperactivity; inattention; processing speed; socioeconomic status.

Figure 1.. Bifactor model of parent-rated ADHD symptoms.

Solid paths are significantly different from zero at p < .01. All point estimates are standardized. Non-significant loadings were dropped in subsequent models. Fit statistics: RMSEA=0.04, χ²(25)=75.18, p<0.001, CFI=0.99, TLI=0.98, SRMR=0.02.

Figure 2.. Standardized regression coefficients of ADHD symptom factors on EF, before and after adjusting for processing speed differences.

Bars represent the 95% confidence intervals. Note. EF.Speed represents EF controlling for effects of processing speed.

Figure 3.. Bifactor ADHD regressed onto executive functioning (EF): (a) before and (b) after accounting for the effects of processing speed.

All point estimates are standardized regression coefficients. Age and sex were included as covariates in these models. The effects of age and sex were controlled for at the factor level for processing speed, the level of first-order factor for EF, and at the indicator-level for ADHD. Fit statistics: (a) RMSEA=0.07, χ²(358)=2985.32, p<0.001, CFI=0.80, TLI=0.77, SRMR=0.14; (b) RMSEA=0.02, χ²(349)=646.57, p<0.001, CFI=0.98, TLI=0.97, SRMR=0.04. Note. Solid paths indicate significance (*p<0.05; **p<0.01).