Structural and Functional Brain Changes Following Repetitive Traumatic Brain Injury: Functional and Molecular Brain Imaging Studies

Abstract

Repetitive traumatic brain injury (rTBI) occurs as a result of mild and accumulative brain damage. A prototype of rTBI is chronic traumatic encephalopathy (CTE), which is a degenerative disease that occurs in patients with histories of multiple concussions or head injury. Boxers have been the most commonly studied patient group because they may experience thousands of subconcussive hits over the course of a match. This study examined the consequences of rTBI with structural brain imaging and biomolecular imaging and investigated whether the neuropsychological features of rTBI were related to the findings of the imaging studies. Five retired professional boxers (mean age, 46.8 ± 3.19) and 4 age-matched controls (mean age, 48.5 ± 3.32) were studied. Cognitive-motor related functional impairment was assessed, and all subjects underwent neuropsychological evaluation and behavioral tasks, as well as structural brain imaging and functional-molecular imaging. In neuropsychological tests, boxers showed deficits in delayed retrieval of visuo-spatial memory and motor coordination, which had a meaningful relationship with biomolecular imaging results indicative of neuronal injury. Morphometric abnormalities were not found in professional boxers by structural MRI, although some diffusion abnormalities were detected in white matter connections from the occipito-temporal and orbitofrontal areas. Striatal dopaminergic function was well preserved. Glucose metabolism was impaired in frontal areas associated with cognitive dysfunction, similar to findings in Alzheimers disease. Low binding potential of 18F-Flumazenil was found in the angular gyrus and temporal cortical regions, revealing neuronal deficits. These results suggested that cognitive impairment and motor dysfunction reflect chronic damage to neurons in professional boxers with rTBI.