PROJECT SUMMARY / ABSTRACT Although concussion or mild Traumatic Brain Injury (mTBI) affects more than a million of Americans each year, and represents a great societal burden, diagnosis is still difficult, and reliable biomarkers are still lacking. The long-term goal is to develop measurable physiological indicators that differ between healthy individuals, and those who sustained an mTBI. The overall objective in this application is to increase the reliability of using eye-movements to diagnose concussion. Circuits in the brain, devoted to vision, vestibular or oculomotor function are so omnipresent in the brain that almost any blow to the head affects sight and eye movements. Therefore, many researchers agree that eye tracking to monitor oculomotor behavior shows great potential of revealing mTBI. Results from studies, using eye movements as a biomarker to predict concussion, are encouraging, albeit not sufficiently strong to proof its clinical utility. The central hypothesis is that the inclusion of microsaccades, the tiny eye movements made when the gaze is fixed on a target, in the continuum of eye movements, will provide an improved technique to diagnose concussion. The central hypothesis will be tested by two specific aims: the first one is to increase the resolution of using eye movements to diagnose concussion. To execute this aim, participants will be recruited among the more than 300 students of Millsaps. They will conduct a ~25-minute oculomotor task while their eye movements are recorded. Athletes who sustain a head injury during the following sports season will then be invited to retake the test. The second aim is to show that monitoring eye movements are also useful in assessing to what extent an individual has recovered from injury. To execute this aim, recovering athletes will be invited to take the oculomotor task weekly. The research proposed in this application is innovative, because microsaccades have been ignored in eye tracking studies; mainly because they require high frequency sampling and specialized software. The applicant possesses both the hard- and software needed to record those elusive eye movements and his preliminary results suggest that including microsaccades will significantly increase the resolution of assessing oculomotor behavior. The research proposed in this application is significant, because eye tracking has been hailed as one of the most promising techniques to obtain a reliable and objective measurement to diagnose concussion, and recording microsaccades has the potential to advance this technique significantly.