Concussion alters communication between the brain’s two hemispheres

A team of researchers discovered that patients who sustained a concussion have microstructural changes in their corpus callosum, which has effect on cognitive function.

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Research has demonstrated that the corpus callosum – which is responsible for transmitting signals between the brain’s left and right hemispheres – is damaged from concussion, however, the effect this has on cognitive function is not fully understood.

Therefore, a team of researchers from New York University (NYU; NY, USA) compared the brains of 36 patients with recent concussions with the brains of 27 healthy controls. Using an innovative advance technique of MRI, which measures water diffusion, they were able to produce a microscopic view of the brain’s signal-carrying white matter.

"Looking at how water molecules are diffusing in the nerve fibers in the corpus callosum and within the microenvironment around the nerve fibers allows us to better understand the white matter microstructural injury that occurs," explained study co-author, Melanie Wegener (NYU).

Wegner and her colleagues also included a second innovative advance in their study, called an Interhemispheric Speed of Processing Task, which is a NYU developed test that evaluates the standard of communication between the two hemispheres.

During the test, participants had to focus their gaze on the letter X that was displayed on a screen directly in front of them. The researchers then displayed 3-letter words either to the left or the right of the X and asked participants to say those words as quickly as they could.

Language function is most often located in the left hemisphere, therefore, information presented to the left visual field is first transmitted to the right visual cortex and then must reach the left language center via the corpus callosum.

The researchers noticed an interesting phenomenon in the reaction times of both groups of participants.

"There is a definite and reproducible delay in reaction time to the words presented to the left of the X compared with words presented to the right visual field," Wegener commented. "This shows it takes time for information to cross the corpus callosum from one hemisphere to the other, which is measured by the difference in response time between words presented to different sides of our visual field."

The participants performance on the test correlated with findings from the team’s MRI technique. The team discovered that the control group’s reaction times corresponded with several diffusion measures in the splenium – an area of the corpus callosum located between the right visual cortex and left language center. However, this correlation was not found in the concussion patients, suggesting they had microstructural changes due to injury.

"We saw a correlation between white matter microstructure injury and the clinical status of the patient," commented Wegener. "This information could ultimately help with treatment in patients who have mild traumatic brain injury."

The findings from this study suggest patients could undergo MRI immediately after a concussion to see if they experienced any clinically important white matter injury and thus may benefit from early intervention. Further, study authors commented on the potential application of MRI during treatment to evaluate treatment-related response.

Source: Radiological Society of North America. Concussion alters how information is transmitted within the brain. Press release: https://press.rsna.org/timssnet/media/rsna/newsroom2019.cfm

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Kimberley Ndungu

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