Washington, March 24 (IANS): In the absence of any definitive diagnostic test, treatment of concussion or 'mild traumatic brain injury' generally depends on symptoms such as headache, nausea, dizziness and confusion.

But researchers have now found that all concussion may not always show symptoms, adding to concerns over the possible long-term effects of repeated, 'subconcussive' brain trauma (causing no concussion symptoms) in humans.

A team of researchers used a standard technique called the 'impact-acceleration model' to induce brain injury in rats.

This technique caused 'diffuse axonal injury' to the brain with visible evidence of damage on the cellular level.

But despite a rather extensive pattern of brain injury, the rats had no significant abnormalities on any of the tests.

"The lack of functional deficits is in sharp contrast to neuro-pathological findings indicating neural degeneration, astrocyte reactivity and microglial activation," said Charles L. Rosen of West Virginia University.

The tests were chosen to reflect symptoms and functions similar to those used to diagnose concussion in humans for such as locomotor activity, coordination, cognitive function, and anxiety and depression-like behaviours.

The study appeared in the journal Neurosurgery.