The loss of white matter connectivity in the brain after severe traumatic brain injury (TBI) may result in impairments in understanding social situations, according to new research published in Brain Imaging and Behavior.

“I have worked as a clinician with people with severe traumatic brain injury for many years. Severe brain injuries usually occur due to high velocity accidents where the brain is abruptly hit against the skull,” said study author Skye McDonald, a professor of clinical neuropsychology at the University of New South Wales.

“There is a tendency for clinicians and researchers to think about the effects of these injuries as focal damage in different areas on the surface of the brain (the grey matter). But the white matter which connects the grey matter is also very vulnerable in a brain injury.”

“The white matter represents the highways and byways of the brain connecting remote areas and connecting the left to the right hemisphere. New imaging techniques, including diffusion tensor imaging, as described in this research, now provide us with the means to visualise the extent to which white matter is damaged,” McDonald told PsyPost.

“Combined with these new imaging techniques, I have a long standing interest in how and why people with brain damage can lose social skills. Social skills are complex, as are social situations. It stands to reason that we need many areas of our brains and good communication between areas in order to have good social skills. So the question arises. Does damage to connections in the brain account for a loss in social cognition?”

The researchers used MRI scans and diffusion tensor imaging to compare the brain structure of 17 adults with chronic, severe TBI to 17 healthy participants of the same age and sex.

The participants also completed an assessment of social cognition, in which they watched people engaging in typical everyday social situations and then answered questions about what the people in the scene were thinking, intending, felt and meant by what they said.

Participants with TBI showed reduced functional connectivity in several brain regions, including but not limited to the corpus callosum and brainstem. Additionally, McDonald and his colleagues found that the loss of white matter connectivity was associated with impairments in social cognition.

“I hope this study demonstrates that connections in the brain are as important as the ‘brain centres’ they connect. People who suffer brain injuries may lose a function, not because a brain centre is damaged, but because connections to that centre may be lost,” he explained.

“I would also hope that people come to appreciate that social behaviour — something we take for granted and engage in seemingly effortlessly — is actually really complex and requires many different abilities. For example, listening to what someone says engages the left cerebral hemisphere. Understanding their emotional state and their tone of voice may require the right hemisphere.”

“These two hemispheres need to be well connected for us to put that information together. The corpus callosum is a white matter tract which connects the two hemispheres is very vulnerable in brain injury and when this is damaged, it causes problems in social reasoning,” McDonald said.

But like all research, the study includes some caveats.

“Our sample was relatively small so we cannot say for sure that our findings apply to all people with brain injuries. The results were correlational only. We cannot say the white matter abnormalities cause social difficulties, only that the two things seem to occur together,” McDonald said.

The study, “Loss of white matter connections after severe traumatic brain injury (TBI) and its relationship to social cognition“, was authored by Skye McDonald, Katie I. Dalton, Jacqueline A. Rushby, and Ramon Landin-Romero.