Concussions used to be thought of as simple injuries. The end of symptoms, such as dizziness and headaches, usually meant a person had fully recovered. Nowhere was this view more prevalent than in sports, where common practice dictated that players could quickly return to the field once the dizziness ended. Now researchers are learning that sports-related concussions are very complicated injuries and that even the mildest ones may cause hidden, long-lasting problems.

“Symptom resolution is not necessarily injury resolution,” said Seymon Slobounov, Ph.D., the Director of the Psychophysiology of Movement Laboratory at Penn State University in University Park, PA. 

Recently, Dr. Slobounov and his team reported the most conclusive evidence to date that an athlete’s brain may remain injured even after the symptoms of a recent concussion have disappeared and that these putative injuries are undetectable by commonly used neuropsychological tests. More importantly, their results suggest that monitoring an athlete’s brain activity with an advanced scanning technique, called rsfMRI, may help assess an athlete’s recovery from a concussion.

Concussion describes the brief loss of consciousness and memory, and dizziness that one may immediately suffer after an abrupt and violent head motion, such as a hit on the head. The traditional view is that once these symptoms have ended, an athlete is ready to return to regular play. However, there is growing concern that sending athletes back onto the field before their brains have fully healed may interfere with their recovery. The problem is that it is very hard to determine whether an athlete’s brain is injured after the symptoms of a concussion have disappeared.

In other words, “there is no gold standard for assessing recovery form a concussion,” Dr. Slobounov said.

Prior studies have used functional magnetic resonance imaging (fMRI) to examine whether there are long-lasting changes in brain activity after a concussion. However, the results have been inconsistent. This may be due to the fact that traditional fMRI measures changes in a small and localized fraction of overall brain activity that is only detectable when subjects are asked to perform a task and that may not be consistently affected by a concussion. 

Dr. Slobounov and his colleagues used a brain imaging technique called resting state fMRI (rsfMRI) to compare the brain activity of athletes who were recovering from a concussion with that of control athletes who had no recent history of a concussion. As the name describes, rsfMRI is done while a person is at rest, which makes it possible to measure the brain’s overall level of activity. The researchers theorized that rsfMRI would allow them to look for larger, more consistent changes in brain activity after a concussion.

The study involved athletes who had experienced a concussion within the previous 10 days but had no residual symptoms. They performed as well as control athletes on neuropsychological and mild exercise tests commonly used to determine whether an athlete has recovered from a concussion.

Nevertheless, rsfMRI brain scans revealed altered patterns of brain activity in the athletes who had suffered a concussion. Much of the activity representing the strength of connections between the left and right halves of the brain was lower, or weaker, than in the uninjured athletes. In contrast to the neuropsychological tests, these results suggested that the injured athletes had not fully healed ten days after the concussion.

When the researchers scanned the athletes’ brains a second time, immediately after administering mild exercise tests, they were surprised to find that the tests affected brain activity similarly in injured and uninjured athletes. The tests strengthened connections between the left and right halves of the brain in both groups. These results suggest that treating concussed athletes with certain mild exercises may need to be studied further.

The corpus callosum, the part of the brain that connects the left and right halves, is commonly affected by more severe traumatic brain injuries. Dr. Slobounov’s results strongly suggest that the corpus callosum may also be the primary site of injury after a concussion.

More importantly, these injuries may not heal until well after the symptoms have passed. These findings further suggest that rsfMRI may improve the assessment of concussed athletes.

Dr. Slobounov and his team received support from the National Institute of Neurological Disorders and Stroke.

–  By Christopher G. Thomas, Ph.D.

Image caption:  A comparison of brain scans taken from an uninjured and a recently concussed athlete reveals potentially harmful changes in brain activity caused by a concussion. The images were captured using a brain scanning technique called resting state functional magnetic resonance imaging (rsfMRI).  Courtesy of Dr. Semyon Slobounov, Penn State University.

Reference:  “Alteration of brain functional network at rest and in response to YMCA physical stress test in concussed athletes: RsFMRI study.” S.M. Slobounov, M. Gay, K. Zhang, B. Johnson, D. Pennell, W. Sebastianelli, S. Horovitz, M. Hallett. NeuroImage, April 15, 2011, Vol. 55(4), pp. 1716-27.

Source : National Institute of Neurological Disorders and Stroke