US military members who are exposed to repeated blasts in a war zone may suffer permanent damage in parts of the brain that lend emotional stability, said a study Wednesday.

Researchers have described mild traumatic brain injury (mTBI) -- more commonly called "concussion" -- as the "signature injury of the wars in Iraq and Afghanistan," said the report in the US journal Science Translational Medicine.

More than 250,000 US service members have been diagnosed with mTBI around the world, and post traumatic stress is a common accompaniment.

Seeking to understand more about how these brain injuries affect the brain, a team of researchers at the VA Puget Sound Health Care System and the University of Washington studied war veterans and found that the more blasts they experienced, the more chronic changes occurred in specific parts of the brain.

They found that repeated exposure to blasts affected the cerebellum, resulting in "persistent dysfunction" in this area of the brain that coordinates movements and also influences a person's emotional state.

Studies on mice showed that those exposed to repeated, mild blasts lost neurons in the same brain regions.

A similar pattern of loss has been documented in retired boxers, going back several decades, the report said.

"Problems with mood, irritability, and impulsivity are very common in our mTBI veterans," said study author Elaine Peskind.

"These findings suggest we should pay more attention to how mTBI affects the cerebellum if we want to fully understand the emotional difficulties experienced by veterans with mTBI."