Long-term effects of mild traumatic brain injuries to oculomotor tracking performances and reaction times to simple environmental stimuli

Abstract

Understanding the long-term effects of concussive events remains a challenge for the development of modern medical practices and the prevention of recurrent traumas. In this study, we utilized indices of oculomotor performance and the ability to react to simple environmental stimuli to assess the long-term motor effects of traumatic brain injury in its mildest form (mTBI). We performed analysis of eye movement accuracy, investigated the presence of abnormal eye movements, and quantified time to react to simple environmental stimuli on long-term mTBI survivors. Results indicated the presence of impairments to basic neural functions used to explore and respond to environmental demands long after the occurrence of mTBIs. Specifically, the result revealed the presence of abnormal saccadic eye movements while performing horizontal smooth pursuit, diminished accuracy of primary saccadic horizontal eye movement, and a widespread slower reaction to both visual and auditory stimuli. The methodology used in this study indicated to be potentially useful in aiding future investigations of neural circuitry impaired by mTBI and provide indices of recovery in future clinical trials testing mTBI-related clinical interventions.

Figure 1

Actual display of recorded eye angular displacement in the horizontal axis from a participant of Control group (panel A) and two participants of mTBI group (panels B and C) performing the horizontal smooth pursuit task. Left and right eye displacements are combined and shown by the blue trace. Black trace shows angular position of stimulus presented. Orange markers identify the presence of saccadic ocular movements while red markers identify data excluded from analysis.

Figure 2

Actual display of recorded left and right eye angular displacement in the horizontal axis from a participant from the Control group (black trace shoes angular position of stimulus presented) (panel A); boxplots from Accuracy Initial Phase Saccade and Reaction Time Saccade recordings obtained for each eye across participants (panels B and C, respectively); and averages across participants for Reaction Time Saccade obtained for all angular displacements (panel D) recorded during the horizontal saccadic movement task. Note: ¹Averages across participants in panels B and C are indicated by the white open circles. ²Traces in panel D represent the linear regression calculated for Angular displacements vs Reaction Time Saccade.

Figure 3

Boxplots from reaction times recorded for simple visual and auditory conditions (panels A and B, respectively) for both experimental groups (Control and mTBI). Averages across participants are indicated by the white open circles.

Figure 4

Example of positioning during data recording (panel A). (1) Eyewear with embedded cameras, (2) Laser emitter, (3) Head rest, and (4) Remote control used for the simple reaction time trials. Schematic representation of superior view of stimuli presentation and participant’s gaze (panel B). Sizes and proportions of figure components have been modified for illustration purposes.