Long-term effects of multiple concussions on prefrontal cortex oxygenation during neurovascular coupling activation in retired male contact sport athletes

PURPOSE: This study aimed to investigate the long-term effects of multiple concussions on prefrontal cortex oxygenation during a neurovascular coupling activating task using near infrared spectroscopy (NIRS). METHODS: Self-reported physically active males who previously participated in contact team sports at various levels of competition and who previously had experienced at least 3 concussions (n = 55; mTBI) or had no history of concussions (n = 29; CTRL) were recruited. Participants completed a 5 min “Where's Waldo” object identification protocol which consisted of participants closing their eyes for 20-s followed by 40-s (repeated 5 times over 5-min) of searching a computer screen for “Waldo” hidden in a field of distractors. NIRS (μM) was used to measure right and left prefrontal cortex cerebral oxygenation. Oxygenated (O(2)Hb), deoxygenated (HHb), total (tHb) haemoglobin, and haemoglobin difference (HbDiff) were analysed through the change in average maximal and minimal values (ΔMAX), Z-scores, and standard deviations. RESULTS: There were no significant differences in the relative change in cerebral oxygenation of the right prefrontal cortex between groups. In mTBI, left prefrontal cortex HHb ΔMAX (p = 0.031) and tHb ΔMAX (p = 0.044) were significantly lower than in the CTRL group. Within-group, right vs. left prefrontal cortex differences showed significantly lower values in left HbDiff Z-scores (p = 0.019) in only the mTBI group while the CTRL group showed significantly lower values in left HbDiff SD (p = 0.045). CONCLUSION: This preliminary study suggests that there are changes in prefrontal cortex oxygenation in males who had a history of experiencing multiple concussions in their past during a neurovascular coupling activating task. These changes may represent potential long-term effects in the brain's ability to adapt cerebral oxygenation during increased neural activity.