Executive Dysfunction after a Sport-Related Concussion Is Independent of Task-Based Symptom Burden

Abstract

The present work examined whether oculomotor deficits associated with a sport-related concussion (SRC) reflect an impairment to executive-based planning mechanisms or a taskbased increase in concussion symptomology (e.g., headache, vertigo). Therefore, I employed a standardized measure of SRC symptom severity (SCAT-5), antisaccade performance and pupillometry metrics in persons with a SRC during early (i.e., initial assessment: ≤12 days post-SRC) and later (i.e., follow-up assessment: 14-30 days post-SRC) stages of recovery. In the initial assessment, the SRC group yielded longer reaction times (RT) (p=0.001), increased directional errors (p=0.002) and larger task-evoked pupil dilations (TEPD) (p=0.004) than the control group. The follow-up assessment indicated that RTs did not reliably vary between groups (p=0.155); however, the SRC group demonstrated more directional errors and larger TEPDs (p<0.03). Moreover, SCAT-5 symptom severity indicated that the oculomotor assessment did not increase symptom burden (p=0.622). Accordingly, I propose that a SRC impairs executive-based oculomotor planning mechanisms.

Pupillometry Reveals the Role of Arousal in a Postexercise Benefit to Executive Function

“…Because video-based tracking systems can distort pupil size following changes in gaze location, this measure was restricted to epochs involving central fixation and prior to saccade initiation (i.e., when gaze was located at the center of the screen). In line with previous work, [14,23,24] pupil size was determined in three epochs prior to saccade initiation (i.e., when gaze was located at the center of the screen): (1) the start of the visual fixation (FIXst; 100-300 ms after fixation onset), (2) maximal pupil constriction (CONmax; 650-750 ms after fixation onset), and (3) end of gap (GAPend; 150-200 ms following gap onset; Figure 1). Dependent variables included the reaction time (RT; time from response cueing to saccade onset), saccade duration (time from saccade onset to saccade offset), percentage of directional errors (i.e., the percentage of trials involving a prosaccade instead of instructed antisaccade and vice versa), baseline pupil diameter (average pupil diameter during FIXst), and task evoked pupil dilation (TEPD; GAPend minus CONmax).…”

“…In support of this, previous work by our lab involving a blocked pro-and antisaccade paradigm with the same target eccentricities demonstrated a selective postexercise antisaccade benefit [13,23,27]. Additionally, another study involving concussed individuals demonstrated evidence of suppressed pro-and antisaccade RTs in a similar interleaved saccade paradigm that were proposed to reflect a concussion-related dysfunction to inhibitory control and cognitive flexibility [23]. Taken together, this evidence supports the stance that the current findings reflect a global improvement to executive function rather than a broader improvement to general cognition.…”

“…In line with the RT findings, the current prosaccade TEPD results provide evidence of a postexercise benefit to cognitive flexibility and task-switching efficiency. In support of this, previous work by our lab involving a blocked pro-and antisaccade paradigm with the same target eccentricities demonstrated a selective postexercise antisaccade benefit [13,23,27]. Additionally, another study involving concussed individuals demonstrated evidence of suppressed pro-and antisaccade RTs in a similar interleaved saccade paradigm that were proposed to reflect a concussion-related dysfunction to inhibitory control and cognitive flexibility [23].…”

“…In reconciling this discrepancy, we note that previous work examined pro-and anti-saccades in separate blocks, whereas the current work randomly interleaved task-type on a trialby-trial basis-a necessary manipulation to prevent TEPD attenuation due to task predictability [26]. As such, the current paradigm not only required the executive demand of response suppression for antisaccade trials, but also the executive component of cognitive flexibility (i.e., task-switching) across antisaccades and prosaccades [13,23,27]. Furthermore, and given that cognitive flexibility and task-switching efficiency elicits a robust postexercise benefit [4,28], it is possible that the postexercise decrease in prosaccade RTs observed here reflects a global benefit to executive function.…”

“…Because video-based tracking systems can distort pupil size following changes in gaze location, this measure was restricted to epochs involving central fixation and prior to saccade initiation (i.e., when gaze was located at the center of the screen). In line with previous work, [14,23,24] pupil size was determined in three epochs prior to saccade initiation (i.e., when gaze was located at the center of the screen):…”