Concussion, or mild traumatic brain injury, is a growing concern especially among the pediatric population. By age 25, as many as 30% of the population are likely to have had a concussion. Many result in long term disability, with some evolving to post-concussion syndrome. Treatments are being developed, but are difficult to assess given the lack of measures to quantitatively monitor concussion. There is no accepted quantitative imaging metric for monitoring concussion. We hypothesized that since cognitive function and fiber tracks are often impacted in concussion, inter-hemispheric brain communication may be impaired. Brain function is linked to changes in oxy- and deoxyhemoglobin.. We used functional near-infrared spectroscopy (fNIRS) to quantify functional coherence between the left and right motor cortex as a marker of inter-hemispheric communication. Studies were undertaken during the resting state and with a finger tapping task to activate the motor cortex. Pediatric patients (age 12 to 18) had symptoms for 21-731 days compared with controls who have not had a reported a previous concussion. We detected a differences between patients and controls in coherence between the contralateral motor cortices using measurements of total hemoglobin with a p< 0.01 (n=8 control, n=12 mTBI). Given the critical need for a quantitative biomarker for recovery following aconcussion, we present this data to highlight the potential of fNIRS coupled with inter-hemispheric coherence analysis as a biomarker of concussion injury.