Investigating Neural Activity Before and After Concussion

At Utah State University’s Learning, Education, & Auditory Processing (LEAP) Brain Imaging Laboratory, Dr. Ron Gillam and Nick Wan, a doctoral student, have begun to study the short-term effects of concussions using functional near-infrared spectroscopy (fNIRS). Although the data are preliminary, the findings are striking: showing greatly increased brain activity following a mild traumatic brain injury (mTBI).

Gillam and Wan came into this line of study by chance. Gillam’s lab was initially piloting an fNIRS study on attention and memory using healthy adolescents and adults. Participants performed two cognitive tasks: the Stroop task, which is designed to test attention, and the n-back task, which is designed to test attention and also working memory. They also performed a number of tasks that were designed to rest the brain. And as it so happened, two of the participants had mild TBI and experienced concussion symptoms soon after being tested.

We had not anticipated this head trauma -- it was unfortunate luck. But after the research assistants found out, they asked whether those participants would volunteer to be tested again while they had these concussion symptoms. They also volunteered for a 4-week follow up with the same tasks.

Gillam’s research group found that the participants performed the attention and memory tasks with the same degree of accuracy before their concussion and immediately after their concussion. However, while the participants had concussion symptoms, they had much greater neural activation as they were doing the attention and memory tasks. When they came back for a 4-week follow up, their neural activation had returned to pre-concussion levels. These findings are very interesting because they show that the participant’s looked fine on behavioral measures after concussion, but their brains were working much harder in order to get the same behavioral results.

scans of a brain before, during, and after a concussion

Participant's brain during attention tasks. Left: Brain before concussion; middle: brain during concussion symptoms; right: brain 4 weeks after concussion.

These findings are in line with previous research on concussions, supporting the “microtearing hypothesis.” According to the microtearing hypothesis, people who have mild TBIs end up tearing or straining areas of the brain where the impact occurred. These microtears result in a sort of brain pathway detour, where pathways for cognitive functions like attention and memory have to use alternate pathways in order to compensate for the detours created due to microtearing. Just like any city, more detours create greater traffic problems. The greater activation during concussion symptoms can be thought of as more traffic in your brain.

When a city detours a regular street, traffic begins to slow. The brain’s version of slow traffic would be an increase in neural resources -- in this case, higher levels of oxygen concentration. We increase the amount of oxygen in an area of the brain in order to compensate for the microtorn pathways. In other words, your brain may be doing more work than usual in order to make you act or behave as if you never were concussed.

Something interesting in these preliminary data is the fact that all participants performed with the same accuracy in all tests; in fact, reaction time was practically the same. These results were not expected, as our intuition suggested less accurate responses and slower reaction times during the concussion symptoms testing.

More research is absolutely needed to better assess all types of concussions -- not just severe ones – but Gillam’s research shows that brain imaging with fNIRS can help supplement the results of behavioral testing, showing problems that would have been missed if behavioral testing was done alone.