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Attention-Deficit/Hyperactivity Disorder (ADHD) is a neurodevelopmental disorder characterized by developmentally inappropriate levels of inattention, hyperactivity, and impulsivity, with three presentations: predominantly inattentive, predominantly hyperactive-impulsive, and combined. ADHD represents primarily a disorder of executive function — particularly working memory, inhibitory control, and cognitive flexibility — rather than of attention per se, as individuals with ADHD can sustain attention to high-interest activities (hyperfocus). The prefrontal cortex and its circuits develop approximately 2–3 years later in individuals with ADHD than in neurotypical peers, making it a developmental delay rather than a developmental deviation. Prevalence is approximately 9–11% in school-age children globally; ADHD has strong heritability (estimated ~70–80%) and is associated with genetic variants affecting dopaminergic and noradrenergic neurotransmission.
Distinguish ADHD from typical developmental inattention and from situational behavior using the DSM-5 cross-situational impairment criterion. Review evidence-based intervention research comparing behavioral therapy, medication (stimulants vs. non-stimulants), and combined approaches across age groups.
To understand ADHD, you first need a clear model of what executive function means. Think of it as the brain's management system — the set of cognitive processes that allow a person to plan, initiate, organize, regulate, and complete goal-directed behavior. The key executive functions implicated in ADHD are inhibitory control (stopping a prepotent response in order to act more deliberately), working memory (holding and manipulating information in mind across brief delays), and cognitive flexibility (shifting between tasks or mental sets). These capacities are primarily implemented by the prefrontal cortex (PFC) and its connections to striatum, cerebellum, and other cortical regions. From your study of adolescent brain development, you know that the PFC is the last brain region to fully mature, completing myelination in the mid-twenties. In individuals with ADHD, this maturation trajectory is delayed by roughly 2–3 years — the cortex eventually reaches the same thickness, but arrives late.
The neurotransmitter basis of ADHD centers on dopamine and norepinephrine circuits. The PFC is particularly sensitive to the concentration of these neurotransmitters: too little or too much both impair function (an inverted-U relationship). Dopamine in the PFC is important for sustaining attention and filtering irrelevant stimuli; norepinephrine modulates the signal-to-noise ratio of incoming information. Stimulant medications (methylphenidate, amphetamine salts) work by increasing synaptic availability of these neurotransmitters — they block reuptake transporters or promote release — which explains why a drug that would make a neurotypical person more alert helps a person with ADHD focus more efficiently. The strong heritability (~70–80%) reflects that many of the genetic variants associated with ADHD affect these dopaminergic and noradrenergic pathways.
The three DSM-5 presentations map to the executive function profile. The predominantly inattentive presentation reflects impairments in working memory and sustained attention — tasks that require holding a goal in mind while filtering distractions. The predominantly hyperactive-impulsive presentation reflects impaired inhibitory control — difficulty stopping responses that feel immediately rewarding in order to pursue delayed goals. The combined presentation involves both profiles. The hyperfocus phenomenon — the ability to sustain intense attention to high-interest activities — seems paradoxical but is consistent with the executive function model: hyperfocus is not controlled attention but a state of automatic engagement that bypasses the executive system entirely. The person with ADHD is not choosing to hyperfocus; the activity is intrinsically stimulating enough that no top-down regulation is required to maintain it.
From your knowledge of developmental screening, you know that diagnosing ADHD requires cross-situational impairment (present in at least two settings), onset before age 12, and ruling out other explanations. The developmental context matters: the same level of inattention that is abnormal for a 10-year-old is normal for a 4-year-old. Effective intervention combines behavioral strategies (which teach compensatory executive function skills and environmental structure), educational accommodations (extended time, reduced distraction), and where indicated, medication. The evidence consistently shows combined approaches outperform either alone, and that medication effects are immediate while behavioral effects accumulate — understanding this timeline is essential for supporting families managing the condition.