Project Details

A Multifaceted Assessment of Post-Concussion Adolescent Startle Response and Injury

Jessie Oldham, PhD

Summary

BACKGROUND: Due to its narrow structure and sensitivity to rotational forces, the brainstem is particularly vulnerable to injury from head impacts. The acoustic startle reflex is a cross-species, brainstem-mediated reflex that may be a sensitive marker for concussion-related brainstem injury. Animal models exhibit a suppressed acoustic startle reflex that extends weeks post-concussion; however, the startle reflex has not been investigated in athletes following concussion. GAP: The acoustic startle reflex has not been investigated following concussion in humans, and this will be the first study to examine the acoustic startle reflex as a potential indicator of post-concussion physiological dysfunction. HYPOTHESIS: Our purpose was to investigate the acoustic startle reflex in a cohort of recently concussed adolescent athletes, those with a concussion history, and healthy controls. We hypothesized that individuals with an acute concussion and those with a history of concussion would exhibit a suppressed startle response compared to healthy controls. METHODS: We conducted a cross-sectional study on 33 adolescent athletes with a recent concussion, a concussion history, and healthy controls. Acoustic startle probes were administered to participants through noise-canceling headphones. The eye blink component of the startle reflex was recorded via electromyography activity of the orbicularis oculi muscle using electrodes placed under the right eye. Measurement sessions began with a one-minute acclimatization period of white noise, followed by twelve 103 decibel acoustic startle probes approximately 50 milliseconds in duration delivered 15-25 seconds apart. The primary dependent variable was mean startle magnitude (µV). We used a one-way analysis of variance followed by a Tukey post-hoc to compare mean startle magnitude between groups. RESULTS: Participants in each group were similar with regards to age and sex (acute concussion n=10, mean age 13.3 ± 3.0 years, 50% female; concussion history n=12, mean age 13.9 ± 3.1 years, 50% female; healthy controls n=11, mean age: 14.8 ± 1.5 years, 55% female). Mean startle magnitude was significantly suppressed in both recently concussed adolescent athletes and those with a concussion history compared to healthy controls (concussion: 77.6 ± 20.6 µV; concussion history: 73.6 ± 28.0 µV, healthy: 176.3 ± 135.5 µV, F=5.98, p=0.007). Significant differences were identified on post-hoc comparisons between the control and concussion group (p=0.01) and control and concussion history group (p=0.02). There was not a significant difference between the concussion and concussion history group (p=0.99). CONCLUSION: Our results provide novel evidence for a distinct suppression of the startle response in adolescent athletes following an acute concussion as well as those with a history of concussion, suggesting there may be lingering physiological dysfunction beyond clinical recovery detectable by startle assessment. IMPACT: The startle reflex could serve as an objective biomarker of brainstem dysfunction following concussion and assist clinicians in making decisions about return to sport, as well as be a predictive tool to help clinicians identify adolescents who are more likely to sustain a subsequent injury following concussion.