Neurological damage is injury or disease that affects the brain. It can be caused by stroke (loss of blood supply), trauma (head injury), tumours, infection or degenerative disease (Alzheimer's, Parkinson's). Studying patients with damage gives unique insight into the function of the affected regions — the foundation of cognitive neuroscience.
Stroke
A stroke is the sudden loss of blood supply to part of the brain, causing neurons to die within minutes.
- Ischaemic stroke (~85% of cases) — a clot blocks an artery.
- Haemorrhagic stroke (~15%) — a blood vessel ruptures.
Symptoms depend on the area damaged. A left-middle-cerebral-artery stroke commonly produces right-side weakness and aphasia (often Broca's or Wernicke's). Recovery depends on plasticity (P2.B.3): neighbouring areas can take on lost roles, especially with intensive rehabilitation.
Famous case studies
Phineas Gage (1848)
A railroad foreman who survived a tamping iron passing through his left frontal lobe. He recovered physically but reportedly underwent a personality change — formerly responsible and well-mannered, he became impulsive, foul-mouthed and untrustworthy ("Gage was no longer Gage").
- Significance — early evidence that the frontal lobes are involved in personality, social judgement and impulse control. Reframed the brain from a single organ to a region-specific one, paving the way for localisation theory (P2.B.4).
- Limitations — single case; reports of his personality change vary in reliability; some accounts may have been exaggerated.
HM (Henry Molaison)
At 27, HM had his hippocampus removed bilaterally to treat severe epilepsy. The seizures stopped — but he could no longer form new long-term episodic memories. He could remember his childhood and learn new motor skills, but every time the researcher entered the room, he greeted her as a stranger.
- Significance — the hippocampus is essential for forming new declarative memories, but procedural memory and STM are dissociable.
Clive Wearing
A British musicologist whose hippocampus was destroyed by viral encephalitis. He has dense anterograde amnesia (cannot form new memories) plus partial retrograde amnesia. He retains his musical skill (procedural memory) and his love for his wife (emotional memory). His diary repeatedly reads "Now I am awake," because every moment feels like the first.
Cognitive neuroscience
Cognitive neuroscience is the scientific study of the biological basis of cognition. It combines:
- Cognitive psychology methods (carefully designed tasks).
- Neuroscience methods (case studies, brain imaging, lesion studies, animal research).
Its central claim: every cognitive process (perception, memory, language, decision-making) corresponds to specific neural activity that can be measured and mapped.
Strengths of case study evidence
- Provides rich, detailed insight into rare conditions.
- Allows ethically impossible "experiments" (we wouldn't damage anyone's brain on purpose) by studying naturally occurring damage.
- Strong support for localisation theory.
Limitations
- Single cases don't generalise easily — Gage may have been atypical.
- Damage is rarely confined to one region — confounding effects.
- Pre-injury baseline data is usually missing.
- Eyewitness reports of personality change can be biased or unreliable.
⚠Common mistakes— Common errors
- Treating Phineas Gage as definitive — he is suggestive, not conclusive.
- Confusing anterograde amnesia (can't form new memories) with retrograde (can't recall old memories).
- Forgetting to link the case to the broader theory it supports (e.g. localisation, multi-store model).
AI-generated · claude-opus-4-7 · v3-deep-psychology