ELECTROPHYSIOLOGICAL SIGNATURES OF SPORTS

ELECTROPHYSIOLOGICAL SIGNATURES OF SPORTS CONCUSSION RECOVERY

M. Mortazavi, SPARCC Sports Medicine, Rehabilitation, and Concussion Center, Tucson, AZ, and Department of Pediatrics Tucson Medical Center, Tucson, AZ; David S. Oakley, WAVi Research, Boulder, CO

Concussion is a major source of sports injury. While there are no objective markers specifi c for the diagnosis of concussion, declines in EEG evoked responses (ERP) have been shown to be highly sensitive to the injury. Moreover, these electrophysical defi cits often linger in patients who otherwise have been determined to have recovered on neuropsychological (NP) and symptomatic assessments. Questions remain, therefore, about recovery prognosis and the extent to which symptom and NP resolution coincides with injury resolution. EEG is the recording of the electrical signal generated by the brain through electrodes placed on the scalp and ERPs are measurements of the EEG signal time-locked to the onset of visual or auditory stimuli. These consist of different components labeled by their polarity (P for positive or N for negative) and their time of occurrence after the stimulus in milliseconds (e.g. P300). The fact that the amplitude of ERP’s declines after concussion and these declines may persist even as symptoms and NP assessments resolve, suggests that concussed participants may recruit additional brain resources to mask their inability to produce the necessary level of amplitude. This implies that functional resolution happens faster than physiological resolution and that current clinical concussion assessment tools may not be sensitive enough to detect subtle concussive defi cits. We present a case series of two athletes drawing from a study of 364 athletes, aged 17-23, participating in contact and collision sports. These subjects were measured with an audio oddball ERP protocol during the course of four seasons at baseline before contact, after concussion, graded return to play, and postseason. Return to play determinations were made via an assessment and management system from the International Symposia on Concussion in Sport using a standard performance and symptom assessment (SCAT) alongside an NP exam. The oddball protocol, one of the most widely studied, utilizes measurements of amplitude and latency to assess the brain’s cognitive ability to recognize an odd tone as different from a common tone where the P300 amplitude is thought to be proportional to the attentional resources devoted to a given task. Using a simple four minute procedure, the 46 subsequent concussion events corresponded to signifi cant changes in P300 amplitude, typically a reduction from baseline, with amplitudes normalizing back to baseline at a rate slower than that observed for NP and symptomatic assessments for 38% of the cases in this blinded study. To illustrate how these trends manifest clinically, we present two acute concussion case studies. These involve two of these NCAA athletes who suffered a concussion during their season, were measured 48 hours post event, and returned to play that season within 1 month. At the time of being cleared according to the assessment and management system, one athlete had returned to their baseline P300 while the other had not. (Anecdotally, it is interesting to note that the player who did not normalize suffered concussions in each of the following 3 seasons).

Fig. 1 P300 magnitude of an athlete at baseline, 48h after a concussive event and at return-to-play 1 month later. Here the P300 voltage is plotted as a function of scalp location. Notice that the P300 decreases after the concussion and increases when the subject cleared for RTP. Fig. 2 P300 magnitude of an athlete at baseline, 48h after a concussive event and at return-to-play 1 month later. Notice that the P300 decreases after the concussion and decreases further when the subject cleared for RTP.

These cases show that while signifi cant decreases in P300 amplitude are often seen after simple concussion, these defi cits may persist even after clearance using standard management protocols. Symptom and NP resolution may not coincide with injury resolution, and other tools such as ERP can be important objective adjuncts.

To access notes on the authors and the research referenced in this article, scan the QR code