Head injury mystery solved

A high school student has helped to solve the long-standing mystery of how the brain is damaged by head injury.

As one might expect the brain is injured at the place where impact takes place during an accident or fall.

But less predictably it is also injured on the opposite side of the head to where the impact took place - and this injury is usually the more severe.

It has been thought that this is simply because the brain first collides against the skull near the point of impact, and then rebounds, hitting the skull at the back.

However, this theory does not explain why the second injury is often worse.

New Scientist magazine reports that Laura Drew, a student at Oakwood High School in Dayton, Ohio, has helped to solve the problem.

Developing an idea put forward by her father William Drew, chief of neurology at the Wright Patterson Air Force Base in Dayton, Laura built a model to simulate what happens inside the head.

Model

Her 'skull' consisted of a tough transparent container filled with a liquid of the same density as the cerebrospinal fluid (CSF) which cushions the brain inside the skull.

The 'brain' was a balloon filled with a slightly less dense saline solution and tethered to the base with a hook.

When the model was propelled into a wall, video footage showed that the momentum of the denser CSF carries it forward, forcing the brain backwards, and into the back of the head.

Only after this impact takes place does the brain rebound and hit the skull at the point where the original blow took place.

This explains why injury on the opposite side of the head - called the contrecoup injury - is usually more severe.

It also explains what happens when someone is hit on the head by, say, a baseball bat.

In this case the head is stationary at the point of impact, and so the brain is not forced backwards to the same extent by a change of momentum. Thus the contrecoup injury will not be noticeably worse than that at the point of contact.

Steve Gilbert, a forensic scientist specialising in brain trauma at the State University of New York in Canton, said the work will help investigators distinguish accidental head injuries from intentional ones.

He said: "Kind of reverses some of the theories, doesn't it?"

Graham Nickson, spokesperson for the charity Headway, told BBC News Online: "There is an awful lot to find out about brain injury.

"If this model helps move us a little further down the road towards understanding how the brain works and how it responds to injury that would be most welcome."