It goes without saying that concussions, or even any notable impact to the brain or cranium can go on to have structural impacts on that precious organ. Inevitably, this would manifest as functional abnormalities as well. Hence, the following recent findings should not come as a surprise:
Research at New York University (NYU) by Wegener et al. (2019) has found that the transmission of information between the two hemispheres of the brain is susceptible to being detrimentally altered by even mild traumatic brain injury (TBI). This stems from the fact that the corpus callosum, is a structure vulnerable to damage in cases of TBI.
Concussion Patients Evaluated
To find out, the team of researchers evaluated the brains of patients with recent bouts of concussion, in comparison with healthy controls, using MRI to measure water diffusion in the corpus callosum nerve fibers, a marker of neuronal activity and axonal integrity (Tsurugizawa, Ciobanu, & Le Bihan, 2013). This (evaluation) was done to gauge the injury at a microscopic level within the white matter.
Concurrent with this MRI technique of analysis, the team conducted an information processing task to assess the degree of interhemispheric communication and corpus callosum function, a task that the researchers designed themselves.
How the test worked was as follows:
The participants had to focus on an “X” on a screen, after which words were flashed to the right and left of the “X.” The participants then had to say those flashed words as quickly as they could.
The key variable being evaluated here was reaction time.
What they found was that there was a noticeable reaction time lag to words flashing to the left of the “X” when compared to the right in concussion patients. This was indicative of some degree of compromise in information crossing over the corpus callosum for the reason of cerebral contralateral organization.
Meaning, the left-right disparity stems from the fact that language function is generally situated at the left hemisphere. Therefore, the information presented on the left side of the participant’s visual field has to be transmitted to the visual cortex on the right side of the brain, after which it has to cross at the corpus callosum to reach the language center in the left hemisphere.
On the other hand, for words on the right side of the participant’s visual field, it is already transmitted to the left side and does not need to cross the corpus callosum. In patients with an intact callosum (the controls), there was, expectedly, no notable information processing lag time.
The results of this task corresponded with MRI findings as well. In healthy controls, water diffusion was duly detected in the corpus callosum, particularly, at the splenium, which is situated between the language center in the left hemisphere and the visual cortex in the right hemisphere.
But in concussion patients, there was a definite disparity in these diffusion measures, which was significantly correlated with performance on the aforementioned processing task. These findings give empirical evidence to how concussion impacts this crucial brain structure, and how it manifests functionally for these, and other concussion victims.
With this said, a delineation between concussion and diffuse axonal injury should be mentioned. Both cases have been associated with injuries spanning the whole corpus callosum. However, a variation in particular regions of the corpus callosum in cases of concussion and diffuse axonal injury has been noted.
In measures of neuronal fiber number, concussion patients have been found to have specific vulnerability in the anterior portion of the corpus callosum connected to the frontal lobe. For patients with diffuse axonal injury, damage has more likely transpired in more diffuse regions of the corpus callosum connected with entire frontoparietal lobes (Jang et al. 2019)
In any case, these most recent findings further corroborate an already intuitive idea: that the corpus callosum is susceptible and often damaged in cases of head trauma, which manifests as compromises in information processing in a left-right dependent manner.
Relevance to Treatment
What we should keep in mind is that concussion patients, once diagnosed, receive almost the exact same treatment. However, no one concussion patient is the same. There are many types of concussion, for which symptoms are generally dependent on the damaged brain region(s), and to what extent it (or they) were damaged.
However, the corpus callosum susceptibility findings seem to establish some common ground among concussion patients in general: that information processing along this conduit is at risk.
What I take from this research, and other studies, is that MRI (with measures of diffusion) can be used to monitor all patients for neuronal damage in different regions of the brain, and allow for monitoring the patient during treatment to see if there is improvement conferred during, and as a result of treatment.
This corpus callosum, because of its apparent vulnerability, should receive extra monitoring. This can be supplemented with the concurrent processing task during follow-up visits. Perhaps incorporating this methodology into patient care for concussion patients could improve the way that these patients recover and preserve neurocognitive functioning now, and in the future.
Jang, S. H., Kim, O. L., Kim, S. H., & Do Lee, H. (2019). Differences in corpus callosum injury between cerebral concussion and diffuse axonal injury. Medicine, 98(41).
Tsurugizawa, T., Ciobanu, L., & Le Bihan, D. (2013). Water diffusion in brain cortex closely tracks underlying neuronal activity. Proceedings of the National Academy of Sciences, 110(28), 11636-11641.
Wegener, M., Bacon, J., Chung, S., Wang, X., Bacon,T., Rath, J., Babb, J., & Lui,Y. Influence of Callosal Microstructural Compromise on Interhemispheric Speed of Processing in Mild Traumatic Brain Injury . Radiological Society of North America 2019 Scientific Assembly and Annual Meeting, December 1 – December 6, 2019, Chicago IL