Steady-State Visual-Evoked Potentials as a Biomarker for Concussion: A Pilot Study

Abstract

A variety of assessment tools are currently available to help clinicians assess Sports Related Concussion (SRC). Currently, the most widely available tools are neither objective nor portable, and are therefore not ideal for assessment at the site and time of a suspected injury. A portable system was developed to deliver a measurement of the steady-state visual-evoked potential (SSVEP). This system involved a smartphone housed in a Google Cardboard frame, which delivered a 15-Hz flicker visual stimulus while an electroencephalography (EEG) headset recorded EEG signals. Sixty-five rugby union players were tested during their regular season and were stratified into healthy, concussed, and recovered groups based on clinical examination. Their SSVEP response was quantified into a signal-to-noise ratio (SNR). The SNRs of players in each study group were summarized. Additionally, the SNRs of individual players who had baseline, post-injury, and post-recovery readings were analyzed. Sixty-five participants completed a baseline evaluation to measure their SSVEP. Twelve of these participants sustained a medically diagnosed concussion and completed SSVEP re-testing within 72 h. Eight concussed players received follow-up SSVEP testing after recovery. Concussed participants had a lower SNR [2.20 (2.04-2.38)] when compared to their baseline [4.54 (3.79-5.10)]. When clinically recovered, participant SNR was not significantly different to their baseline [4.82 (4.13-5.18)]. The baseline SNRs of the players who experienced a concussion during the season were not different to those of players who did not experience a concussion [4.80 (4.07-5.68)]. This is the first study to identify differences in SSVEP responses in male amateur rugby union players with and without concussion. It is also the first SSVEP demonstration for concussion evaluation at point-of-care. SSVEPs are significantly attenuated in the presence of concussion in these male athletes. Individuals returned to their baseline SSVEP following clinical recovery from the concussive injury. The use of SSVEPs has the potential to be a supplemental aid for the assessment and management of concussion.

Keywords: SSVEP; concussion; electroencephalography; football; sport.

FIGURE 1

Flowchart of screening for participant eligibility and allocation throughout the study duration of amateur rugby union players.

FIGURE 2

(A) An example of the visual stimulus. The stimulus alternated between the top and bottom picture at a rate of 15 times per second. There is a fiducial line in the middle used to align the screen with the Google Cardboard headset. The number at the center of each square changed at 5 s intervals and participants were instructed to focus on the number for a total of 30 s. NB, The shadow does not exist on the actual stimulus but is utilized here to make the visual stimulus clearer to view. (B) Emotiv EPOC+ electrode positions (Liu et al., 2012). Only electrodes P3 (CMS), P4 (DRL), O1, and O2 were utilized: P3 and P4 were utilized as a common-mode subtraction/driven-right-leg reference and ground, and O1 and O2 were the analyzed electrodes.

FIGURE 3

Average Fourier transformation of the frequency spectrum (SSVEP) of all 65 control players (baseline). This includes the retest results of the non-concussed players. SNR, signal to noise ratio.

FIGURE 4

Fourier transformations of the frequency spectrum (SSVEP) comparisons of player JJ2 for baseline (Left), concussed (Center), and when clinically recovered (Right). Note the presence of a peak at 15 Hz on the left and right figures, demonstrating a response to the 15 Hz visual stimulus. SNR for each reading is also noted for each graph. SNR; signal to noise ratio.