2 Neuroscience2.7 Neural circuits
2.7.1.12 Attention and its impairment in ADHD
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Written by Resident Doctor Committee · Published
Components of attention
Posner's three operations can fail separately.
Component | Operation | Main systems |
|---|---|---|
Alerting | Readiness to respond | Locus coeruleus, thalamus, right frontoparietal cortex |
Orienting | Selecting location, modality or object | Superior colliculus, pulvinar, frontoparietal networks |
Executive control | Holding rules, resolving conflict, inhibiting responses | Prefrontal cortex, cingulate, basal ganglia |
Type | Feature |
|---|---|
Sustained | Holds performance over time; fatigue and monotony erode it |
Selective | Prioritises relevant information over distractors |
Divided | Shares resources; harder when tasks use similar operations |
Endogenous | Goal-directed |
Exogenous | Captured by external events |
Noradrenaline and arousal
The locus coeruleus supplies noradrenaline: tonic activity sets background arousal, and phasic bursts mark relevant or unexpected events.
Performance follows an inverted U: moderate tonic activity with clear phasic bursts sharpens signals, and too little or too much impairs it.
Orienting networks
Network | Anatomy | Function |
|---|---|---|
Dorsal | Intraparietal and superior parietal cortex, frontal eye fields | Goal-directed orienting to locations and features |
Ventral (right-lateralised) | Temporoparietal junction, ventral frontal cortex | Reorienting to relevant unexpected events |
Left neglect can follow right parietal damage even without a visual field deficit; it is a failure of spatial attention, not eye movement.
Executive control
The dorsolateral prefrontal cortex holds task rules, the cingulate monitors conflict and errors, and right inferior frontal networks stop actions.
Poor coordination between default mode activity, which normally falls during demanding tasks, and task networks may cause lapses.
Impairment
Attention deficit hyperactivity disorder (ADHD) is developmentally inappropriate regulation of attention, activity and impulses, not absent attention.
Circuit | Contribution |
|---|---|
Frontostriatal | Response selection, inhibition, delay sensitivity |
Frontoparietal | Goal maintenance, attention |
Cerebellar | Timing, prediction |
Group studies show varied maturation, including later peak cortical thickness in some regions, rather than a single lesion.
Dopamine modulates working memory and reinforcement learning; noradrenaline affects arousal and prefrontal control.
Reaction times are more variable, with occasional long lapses, and some groups show weaker inhibition or prefer immediate rewards.
Limits of individual inference
Sleep problems, anxiety, learning difficulties, trauma, substances and depression can mimic or coexist with ADHD.
Imaging and cognitive tests show overlapping group distributions and cannot diagnose ADHD alone; nor does response to medication.
Diagnosis rests on developmental history, symptoms and functional impairment across settings.