Executive Functions

Diamond (2013) identifies three core EFs: (1) Inhibitory control — suppressing dominant/automatic responses, resisting temptation, and filtering irrelevant information; measured by Stroop, stop-signal, and Go/No-Go tasks. (2) Working memory — holding and manipulating information in mind; measured by n-back tasks, digit span backwards, and complex span tasks. (3) Cognitive flexibility (shifting) — switching between tasks or mental sets; measured by WCST and task-switching paradigms. These three are "core" because they are relatively independent of each other (dissociable), have distinct neural substrates, and serve as building blocks for higher-order EFs like planning, reasoning, and fluid intelligence.

ADHD is characterised primarily by deficits in inhibitory control and working memory — two of the three core EFs. Russell Barkley (1997) proposed that ADHD is fundamentally a disorder of behavioural inhibition: the inability to inhibit prepotent responses, ongoing behaviour, and interference from competing stimuli impairs the four executive functions that depend on inhibition (working memory, internalisation of speech, emotion regulation, and reconstitution). Children with ADHD consistently show impaired performance on Stroop and stop-signal tasks, reduced working memory capacity, and poor set-shifting. Stimulant medications (methylphenidate, amphetamine) increase dopamine and noradrenaline in the PFC, directly improving EF performance.

Executive functions rely primarily on prefrontal cortex (PFC) circuits, with contributions from parietal cortex and basal ganglia. The dorsolateral PFC (DLPFC) is particularly important for working memory maintenance and cognitive flexibility. The ventrolateral PFC (VLPFC) and inferior frontal gyrus are critical for inhibitory control. The anterior cingulate cortex (ACC) monitors conflict and errors, signalling the need for increased executive control. The orbitofrontal cortex integrates reward and emotional information with executive processing. Basal ganglia contribute to inhibitory control and set-shifting through their connections with PFC. Damage to any of these nodes — as in focal lesions, ADHD, or schizophrenia — produces characteristic EF deficits.

This remains debated. Short-term laboratory training on working memory tasks (e.g., n-back) produces reliable near-transfer improvements on the trained task and closely similar tasks. However, far transfer — improvements in untrained EF tasks, academic achievement, or fluid intelligence — is modest and often absent, particularly after longer follow-up periods. A 2013 meta-analysis by Melby-Lervåg and Hulme found that WM training produced no reliable far transfer. Broader EF training incorporating multiple tasks, alongside physical activity and self-regulation training, shows more promise, particularly in children with initial EF deficits. Activities with simultaneous cognitive and physical demands — certain martial arts, organised sports, musical training — show some evidence of EF improvements.