Abstract
Both Attention-Deficit/Hyperactivity Disorder (ADHD) and Obsessive-Compulsive Disorder (OCD) are associated with choice impulsivity, i.e. the tendency to prefer smaller immediate rewards over larger delayed rewards. However, the extent to which this impulsivity is mediated by shared or distinct underlying neural mechanisms is unclear. Twenty-six boys with ADHD, 20 boys with OCD and 20 matched controls (aged 12–18) completed an fMRI version of an individually adjusted temporal discounting (TD) task which requires choosing between a variable amount of money now or £100 in one week, one month or one year. Activations to immediate and delayed reward choices were compared between groups using a three-way ANCOVA. ADHD patients had steeper discounting rates on the task relative to controls. OCD patients did not differ from controls or patients with ADHD. Patients with ADHD and OCD showed predominantly shared activation deficits during TD in fronto-striato-insular-cerebellar regions responsible for self-control and temporal foresight, suggesting that choice impulsivity is mediated by overlapping neural dysfunctions in both disorders. OCD patients alone showed dysfunction relative to controls in right orbitofrontal and rostrolateral prefrontal cortex, extending previous findings of abnormalities in these regions in OCD to the domain of choice impulsiveness.
Highlights
Impulsivity is a multifaceted construct and is typified by a premature, poorly controlled, delay averse response pattern where the consequences of acts are poorly considered (Fineberg et al, 2014; Rubia, 2002; Rubia et al, 2009)
The findings show that patient groups relative to controls, shared underactivation in key regions of self-control and temporal foresight (Noreika et al, 2013; Rubia et al, 2009), including right inferior frontal gyrus (IFG), dorsolateral prefrontal cortex (DLPFC), anterior insula (AI), dorsal striatum and bilateral cerebellum during delayed choices
The findings suggest that key mechanisms associated with adaptive reward-related decision making and temporal foresight during temporal discounting (TD) are impaired in both disorders, while orbitofrontal cortex (OFC) and rostrolateral prefrontal cortex (RLPFC) regions are exclusively impaired in Obsessive-Compulsive Disorder (OCD)
Summary
Impulsivity is a multifaceted construct and is typified by a premature, poorly controlled, delay averse response pattern where the consequences of acts are poorly considered (Fineberg et al, 2014; Rubia, 2002; Rubia et al, 2009). It has been investigated as a potential correlate of both Attention-Deficit/Hyperactivity Disorder (ADHD) and Obsessive-Compulsive Disorder (OCD), disorders which affect around 3–8% and 1–3% of children respectively, as well as around 4% (ADHD) and 2% (OCD) of adults (Biederman et al, 2012; Ruscio et al, 2010). In OCD, increased self-reported impulsivity is associated with poorer treatment outcomes (Kashyap et al, 2012)
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