Concussion, Brain Injury and CTE

From mild concussion to severe traumatic brain injury: what happens when the brain is jolted, why rest and gradual return matter, and the discovery of chronic traumatic encephalopathy in athletes.

What happens in an injury

Traumatic brain injury (TBI) is damage caused by an external force — a fall, car crash, assault, sports collision or blast. The brain floats in fluid inside a hard skull; a sudden acceleration, deceleration or rotation can make it strike the skull and twist, stretching and damaging axons (diffuse axonal injury), bruising tissue and tearing blood vessels. TBIs range from mild (most concussions) to moderate and severe, which may cause prolonged unconsciousness and lasting disability.

Concussion

A concussion is a mild TBI. Most people don't lose consciousness. Symptoms include headache, dizziness, nausea, confusion, feeling "foggy", memory gaps around the event, sensitivity to light and noise, sleep changes and irritability. Standard brain scans are usually normal — the injury is mostly at the level of cells and connections, with a temporary energy crisis as ion balances are disrupted. Most people recover within a few weeks; a minority have persisting symptoms.

Current guidance recommends a short period of relative rest, followed by a gradual, staged return to activity, school and sport — light activity early is now considered helpful rather than complete rest. A second blow before recovery is dangerous: rarely, especially in young people, it can cause catastrophic brain swelling ("second impact syndrome"). The safest rule in sport: "if in doubt, sit them out."

CTE

In 1928 the pathologist Harrison Martland described "punch drunk" boxers with tremor, confusion and personality changes. In 2005 the pathologist Bennet Omalu reported abnormal tau protein in the brain of former NFL player Mike Webster, describing chronic traumatic encephalopathy (CTE) in American football. CTE is a degenerative disease linked to repeated head impacts, including many that don't cause recognised concussions. It is marked by tau build-up around small blood vessels in the depths of the cortical folds, and is associated with problems in mood, behaviour, memory and thinking. A 2023 Boston University report found CTE in the brains of 345 of 376 former NFL players studied — though donated brains are not a random sample. CTE can currently be definitively diagnosed only after death; research on diagnosing it in life is under way.

Prevention

Rule changes (limiting heading in youth football/soccer, reducing contact in practice), better concussion protocols, seatbelts, helmets for cycling, and preventing falls in older adults all reduce brain injuries.