Brain Recovery: The Good then the Bad

Study reveals two-phase brain response after moderate to severe injury: recovery, then decline.

Recent findings from the KITE Research Institute provide a detailed view into how the brain changes after moderate to severe traumatic brain injury over the long-term. 

The research team measured brain connectivity—the connections between different brain regions— from five months to several years in individuals who experienced brain injury. The team found that connectivity increases initially, but only to a point. At around one and a half years after injury, the brain seems to reverse course and lose connectivity, suggesting a decline in brain function.

“Our findings support growing evidence that moderate to severe brain injury—over the long term—can lead to behavioural declines and loss of brain function,” says Isis So, the first author and a former graduate student in the lab of KITE Senior Scientist Dr. Robin Green.

The research team followed the recovery of forty adults who experienced brain injury. The team took brain scans of these individuals at different times—at half a year, at one to one and a half years, and at three years or more after injury. 

Functional magnetic resonance imaging (fMRI) was used to measure brain connections in two brain networks—the frontoparietal network and the default mode network. These networks were chosen because they are involved in higher brain functions such as short-term memory. 

“Few studies have measured brain connectivity and recovery over longer time points in people with moderate-severe traumatic brain injury. Our study is one of the first to measure brain connectivity changes beyond six months post-injury,” says Dr. Robin Green, the senior author.

“Combined with our previous findings, the current findings suggest that the brain is not static in the chronic stages of injury, contrary to previous assumptions. Moreover, the findings indicate that both reparative and deteriorative neural mechanisms are operating in the first few years of injury, but that in the later chronic stages, the deteriorative mechanisms predominate.”

“By identifying that there are factors at play that are causing cognitive decline, and studying what causes or exacerbates them, we can explore potential therapeutic strategies. This could greatly improve the lives of individuals that experience brain injury,” adds Dr. Green. 

This work was supported by Dr. Green’s previous Canada Research Chair and current Saunderson Family Chair, the Physician’s Services Foundation (PSO), the Natural Sciences and Engineering Research Council of Canada, the Sorbara Family Foundation, the Walter Schroeder Family Foundation, and UHN Foundation. Dr. Robin Green is a Professor of Psychiatry at the University of Toronto (UofT); and an Associate Member at UofT's Rehabilitation Sciences Institute, Program in Neurosciences, Institute of Medical Sciences, and Graduate Department of Psychological Clinical Science (UofT Scarborough).

So I, Meusel LA, Sharma B, Monette GA, Colella B, Wheeler A, Rabin JS, Mikulis D, Green RE. Longitudinal Patterns of Functional Connectivity in Moderate-to-Severe Traumatic Brain Injury. J Neurotrauma. 2022 Nov 11. doi: 10.1089/neu.2022.0242. Epub ahead of print. PMID: 36367163.

 The brain’s default mode network only becomes active when we slow down, reflect and let our minds wander. It is thought to be important to various modes of thought, including when we think about ourselves or others, and when we remember the past or think about the future.