Researchers in the US have discovered brain injury alters 'master genes' in the brain that control genes linked to Alzheimer's disease, ADHD and depression.

Head injuries can harm hundreds of genes in the brain, increasing a person's risk of neurological and psychiatric disorders, according to a US study.

Researchers at the University of California have identified "master genes" they believe control hundreds of other genes linked to Alzheimer's disease, Parkinson's disease, post-traumatic stress disorder, stroke, attention deficit hyperactivity disorder, autism, depression, schizophrenia and other disorders.

It's hoped the knowledge could eventually mean scientists will be able to learn how to re-modify or repair damaged genes through the use of drugs and foods and reduce the risk of brain disease.

"Very little is known about how people with brain trauma - like football players and soldiers - develop neurological disorders later in life," said Fernando Gomez-Pinilla, a UCLA professor of neurosurgery and of integrative biology and physiology.

"We hope to learn much more about how this occurs," he said.

As part of the study, published in EBioMedicine, the researchers trained 20 rats to escape from a maze. They then used a fluid to produce a concussion-like brain injury in 10 of the rats; the 10 others did not receive brain injuries.

When the rats were placed in the maze again, those that had been injured took approximately 25 per cent longer than the non-injured rats to solve it.

To learn how the rats' genes had changed in response to the brain injury, the researchers analysed genes from five animals in each group.

In the rats with brain injuries, there was a core group of 268 genes in the hippocampus that had been altered, and a core group of 1215 genes in the white blood cells that had also been changed.

"A surprise was how many major changes occurred to genes in the blood cells," said senior author Associate Professor Xia Yang.

"The changes in the brain were less surprising. It's such a critical region, so it makes sense that when it's damaged, it signals to the body that it's under attack."

While the study was on rats, more than 100 of the genes that changed after the brain injury have counterparts in humans that have been linked to neurological and psychiatric disorders, the researchers reported.

Ass Prof Yang said the study not only indicated which genes are affected by traumatic brain injury and linked to serious disease, but also might point to the genes that govern metabolism, cell communication and inflammation, which might make them the best targets for new treatments for brain disorders.