Calvin Zhuhan Qiao
Doctor of Philosophy in Mechanical Engineering (PhD)
Investigating Vestibular Changes After Subconcussive Head Impacts
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Soccer heading is a common technique where players use their head to pass, shoot or clear the ball. The ball-to-head impact involved in this technique has raised concern for risk of head and brain injury. However, there are inconclusive findings on the effect of soccer headers in the literature. The objective of this study was to investigate, in a controlled environment, whether mild soccer head impacts result in immediate neurophysiological changes in the brain, and if yes, whether the changes are affected by impact level and header direction. Controlled soccer headers were simulated at 2 impact levels in 3 directions, representative of the mildest headers experienced on the field, using a custom pendulum impactor with a soccer ball attachment. Participants were instrumented with an inertial measurement unit (IMU) to record the head kinematics of head impacts and an electroencephalography (EEG) device to measure neurophysiological changes. The EEG changes were evaluated by four metrics (absolute and relative power, magnitude squared and imaginary coherence) for common brain wave frequency bands. With data from 8 participants (6 males, 2 females), the study provided statistically significant evidence of the immediate neurophysiological changes after mild soccer headers. We found a surge in normalized absolute power right after heading across all the frequency bands with a larger increase for headers at the higher impact level. In addition, we observed an increase in delta band relative power, along with a decrease in the higher frequency bands, indicating slowing of activity in the brain. These findings are consistent with those observed in patients with traumatic brain injury or post-concussive syndrome. Aside from changes in power, we also found evidence of significant changes in coherence with different patterns between magnitude squared and imaginary coherence, suggesting effects of heading on the brain’s functional connectivity. Finally, we found evidence that these changes diminished over time and participant’s neurocognitive performance remained unchanged. Our findings suggest that even mild soccer headers could lead to immediate, transient neurophysiological changes and highlight the importance of further investigation of the effects of long-term head impact accumulation in sports.