What is the Cognitive Deficit in Sluggish Cognitive Tempo (SCT)? A Review of Neuropsychological Research

Both performance-based and rating measures are commonly used to index executive function in clinical and neuropsychological assessments. They are intended to index the same broad underlying mental construct of executive function. The association between these two types of measures was investigated in the current article. We examined the association between performance-based and rating measures of executive function in 20 studies. These studies included 13 child and 7 adult samples, which were derived from 7 clinical, 2 nonclinical, and 11 combined clinical and nonclinical samples. Only 68 (24%) of the 286 relevant correlations reported in these studies were statistically significant, and the overall median correlation was only .19. It was concluded that performance-based and rating measures of executive function assess different underlying mental constructs. We discuss how these two types of measures appear to capture different levels of cognition, namely, the efficiency of cognitive abilities and success in goal pursuit. Clinical implications of using performance-based and rating measures of executive function are discussed, including the use of these measures in assessing ADHD. © 2012 The Authors. Journal of Child Psychology and Psychiatry © 2012 Association for Child and Adolescent Mental Health.

Individuals with ADHD are characterized as ubiquitously slower and more variable than their unaffected peers, and increased reaction time (RT) variability is considered by many to reflect an etiologically important characteristic of ADHD. The present review critically evaluates these claims through meta-analysis of 319 studies of RT variability in children, adolescents, and adults with ADHD relative to typically developing (TD) groups, clinical control groups, and themselves (subtype comparisons, treatment and motivation effects). Random effects models corrected for measurement unreliability and publication bias revealed that children/adolescents (Hedges' g=0.76) and adults (g=0.46) with ADHD demonstrated greater RT variability relative to TD groups. This increased variability was attenuated by psychostimulant treatment (g=-0.74), but unaffected by non-stimulant medical and psychosocial interventions. Individuals with ADHD did not evince slower processing speed (mean RT) after accounting for RT variability, whereas large magnitude RT variability deficits remained after accounting for mean RT. Adolescents and adults with ADHD were indistinguishable from clinical control groups, and children with ADHD were only minimally more variable than clinical control children (g=0.25). Collectively, results of the meta-analysis indicate that RT variability reflects a stable feature of ADHD and other clinical disorders that is robust to systematic differences across studies. Copyright © 2013 Elsevier Ltd. All rights reserved.

Controversy continues as to whether sluggish cognitive tempo (SCT) is a subtype of attention-deficit/hyperactivity disorder (ADHD) or a distinct disorder. This study examined differences between these disorders in demographics, executive functioning (EF), impairment, and prior professional diagnoses to address the issue. There were 1,800 children 6 to 17 years of age of both sexes from various U.S. ethnic backgrounds who were divided into four groups: (a) high SCT but not ADHD (N = 41), (b) high ADHD but not SCT (N = 95), (c) high in both SCT and ADHD (N = 61), and (d) the control group (N = 1,603). Besides providing demographics, parents completed scales assessing ADHD and SCT symptoms, EF deficits, and psychosocial impairment and reported their child's history of professional diagnoses. SCT symptoms formed two distinct but interrelated factors separate from those for ADHD. SCT differed from ADHD in demographics (age, sex ratio, parental education, income). ADHD was associated with more severe and pervasive EF deficits than SCT, whereas SCT was chiefly associated with mild deficits in Self-Organization. ADHD contributed far more variance to EF deficits than did SCT. Both disorders were impairing, but ADHD was more severely and pervasively so than SCT, especially in Home-School domains; SCT was most impairing in Community-Leisure domains. Different patterns of comorbidity were evident between SCT and ADHD. SCT showed less comorbidity and was particularly associated with depression. SCT may comprise a distinct disorder from ADHD but both may coexist in 39% to 59% of cases each.