O3285: Functional Near Infrared Spectroscopy Distinguishes Concussed from Healthy Individuals Performing Complex Tandem Gait

Background: Functional near infrared spectroscopy (fNIRS) detects differences in task-based cortical activation and has been demonstrated to distinguish concussed from healthy individuals in a visual task. The goal of this study was to determine whether fNIRS could identify differences in cortical activation between concussed and healthy adolescents performing a balance-oriented motor task, complex tandem gait, which has demonstrated clinical validity as a diagnostic behavioral assessment in concussion.

Methods: We recruited 111 individuals with concussion, ages 7 to 21 years, mean age 15, 54% female and; 163 healthy control subjects, ages 10-21 years, median age 15, 53% female from a subspecialty referral concussion program and a regional secondary school for this prospective cohort comparison. The participants performed the complex tandem gait task, walking heel-to-toe forwards, eyes open and closed, and then backwards, eyes open and closed, for a total of four task conditions while wearing the fNIRS device. For each participant, the raw light intensity data from each optode of fNIRS were low-pass filtered to attenuate high frequency noise and physiological artifacts such as respiration and cardiac cycle effects. Motion artifacts were removed via a sliding-window motion artifact rejection algorithm (Ayaz et al 2010). For each task block, the raw light intensity data was extracted using time synchronization markers. The relative changes in oxy-and deoxy-hemoglobin concentrations over each task period for each optode were calculated via the Modified Beer Lambert Law using baseline from the beginning of the task session. The average oxy-hemoglobin concentration changes for each task condition period were used for statistical analysis of the group and task effect. A linear mixed effects model with restricted maximum likelihood was used to estimate the effects on both cerebral hemodynamics with the subject as a random effect.

Results: Oxygenated hemoglobin changes, as detected by fNIRS, indicated a significant interaction of group (concussed cases vs. healthy controls) and complex tandem gait task condition (F3,617.8=17.06, p< 0.00001) in the anterior prefrontal cortex. Posthoc analysis indicated significant group differences for each task1 (F1,379.5=31.45, p< 0.00001), task2 (F1,375=30.91, p< 0.00001) and task3(F1,377.7=26.06, p< 0.00001).

Conclusion: Greater cortical activation was observed in concussed individuals across all complex tandem gait task conditions compared to healthy controls indicating that fNIRS, as a modality, distinguishes those with concussion. The habituation pattern observed in healthy individuals is not seen in those with concussion indicating that compensatory measures are required to complete the same task after injury. This may be useful in the future both as a diagnostic and potential recovery biomarker.