Mechanisms underpinning inattention and hyperactivity: neurocognitive support for ADHD dimensionality

Abstract

Background. Taxometric and behavioral genetic studies suggest that attention deficit hyperactivity disorder (ADHD) is best modeled as a dimension rather than a category. We extended these analyses by testing for the existence of putative ADHD-related deficits in basic information processing (BIP) and inhibitory-based executive function (IB-EF) in individuals in the subclinical and full clinical ranges. Consistent with the dimensional model, we predicted that ADHD-related deficits would be expressed across the full spectrum, with the degree of deficit linearly related to the severity of the clinical presentation.Method. A total of 1547 children (aged 6-12 years) participated in the study. The Development and Well-Being Assessment (DAWBA) was used to classify children into groups according to levels of inattention and hyperactivity independently: (1) asymptomatic, (2) subthreshold minimal, (3) subthreshold moderate and (4) clinical ADHD. Neurocognitive performance was evaluated using a two-choice reaction time task (2C-RT) and a conflict control task (CCT). BIP and IB-EF measures were derived using a diffusion model (DM) for decomposition of reaction time (RT) and error data.Results. Deficient BIP was found in subjects with minimal, moderate and full ADHD defined in terms of inattention (in both tasks) and hyperactivity/impulsivity dimensions (in the 2C-RT). The size of the deficit increased in a linear manner across increasingly severe presentations of ADHD. IB-EF was unrelated to ADHD.Conclusions. Deficits in BIP operate at subclinical and clinical levels of ADHD. The linear nature of this relationship provides support for a dimensional model of ADHD in which diagnostic thresholds are defined in terms of clinical and societal burden rather than representing discrete pathophysiological states.

Association between irritability and bias in attention orienting to threat in children and adolescents

“…In sum, the present report extends previous work from the HRC (Salum et al., ), as this is the first analysis in that, or any other, community‐based sample to examine associations between irritability and attention bias to threat. Our main hypothesis is that irritability is associated with increased attention to threat cues.…”

Heterotypic trajectories of dimensional psychopathology across the lifespan: the case of youth‐onset attention deficit/hyperactivity disorder

“…Diffusion models were used to decompose 2C‐RT into the distinct components of basic information processing: processing efficiency (determined by the drift rate), speed‐accuracy trade‐off (measured as boundary separation) and encoding/motor function (measured as nondecision time). Previous investigations (Salum, Sergeant, et al., ; Salum, Sonuga‐Barke, et al., ) showed important basic processing differences in children with distinct levels of ADHD symptomatology. More information on this methodology can be found in other publications (Salum, Sergeant, et al., ; Salum, Sonuga‐Barke, et al., ).…”

“…Previous investigations (Salum, Sergeant, et al., ; Salum, Sonuga‐Barke, et al., ) showed important basic processing differences in children with distinct levels of ADHD symptomatology. More information on this methodology can be found in other publications (Salum, Sergeant, et al., ; Salum, Sonuga‐Barke, et al., ).…”

“…Corroborating our post‐hoc hypothesis, adolescents with youth‐onset ADHD have not only more symptoms in both parent and teacher reports, but also lower cognitive and school performance than community comparisons as children, before they reach the diagnostic threshold. It was known that these dysfunctions are important components of the neuropsychology of ADHD (Salum, Sergeant, et al., ; Salum, Sonuga‐Barke, et al., ; Willcutt, Doyle, Nigg, Faraone, & Pennington, ). These findings on early cognitive markers were not found in previous cohort studies but might be relevant for adolescent‐onset ADHD.…”

COMT and DAT1 genes are associated with hyperactivity and inattention traits in the 1993 Pelotas Birth Cohort: evidence of sex-specific combined effect

“…43 In addition, deficits in basic information processing were found to be linearly associated with ADHD severity that ranged from asymptomatic to clinical ADHD. 44 A twin study provided evidence of an additive genetic pattern of ADHD inheritance because the observed concordance rates between dizygotic twins were around half of those observed in monozygotic twins. 3 This is consistent with the idea that genetic variants of small effect, either common or rare, together contribute to build a genetic risk for a given psychiatric disorder.…”