Neuropsychological, Metabolic, and GABAA Receptor Studies in Subjects with Repetitive Traumatic Brain Injury

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 injuries. Boxers have been the most commonly studied patient group because they may experience thousands of subconcussive hits over the course of a career. 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 years) and four age-matched controls (mean age, 48.5 +/- 3.32 years) 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 visuospatial 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 magnetic resonance imaging (MRI). Glucose metabolism was impaired in frontal areas associated with cognitive dysfunction, similar to findings in Alzheimer's disease. Low binding potential (BP) of F-18-flumazenil (FMZ) 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.