A single severe head injury can trigger long-term brain damage

One major blow to the head is enough to trigger progressive brain deterioration and long-term cognitive decline in some people.

We already know that repeated head knocks – like those sustained in boxing and American football – can lead to personality changes, cognitive problems and depression years later. This condition – known as chronic traumatic encephalopathy (CTE) – is associated with gradual build-up of a protein called tau in the brain.

David Sharp at Imperial College London and his colleagues wondered if similar brain changes can occur after one bad head injury.

To find out, they scanned the brains of 21 men and women who had a single major head injury 18 to 51 years ago in a car accident, assault or fall. They all experienced severe initial symptoms like loss of consciousness for more than 30 minutes, and many have since developed problems with thinking, memory and motivation.

The scans revealed that 15 of the participants have unusually high levels of tau protein in their brains, particularly in the outer layers. This is probably because the outer layers are most vulnerable to external impacts, Sharp’s team writes.

The amount of tau in their brains didn’t seem to relate to symptom severity, but the study may have been too small to detect this relationship, say the researchers.

Dose dependent

High levels of tau have also been found in the outer brain layers of former athletes with CTE, particularly in those who have had the most head blows. This is consistent with the idea that brain deterioration can come from either several relatively minor brain injuries or from a single particularly severe one, writes the team.

Both types of head injury probably damage brain structures called microtubules that are stabilised by tau proteins, say the researchers. This, in turn, could make the tau proteins turn rogue and start forming large tangled clumps that gradually harm the rest of the brain.

At the moment, there are no treatments to slow or reverse brain deterioration following head injuries, but medications like antidepressants can sometimes help to relieve the symptoms of CTE.