Attentional disengagement dysfunction following mTBI assessed with the gap saccade task.

Concussion, or mild traumatic brain injury (mTBI), leads to a number of cognitive, attentional, and sensorimotor deficits that can last a surprisingly long time after the initial injury. We have previously shown that the ability to orient visuospatial attention is deficient in participants with mTBI within 2 days of their injury, but then recovers to normal levels within a week. Orienting attention requires disengagement from the point of fixation, movement of attention to the location of interest, and re-engagement at that location. Deficits in any or all of these processes could lead to the difficulties with orienting attention that we have observed in mTBI. To address this issue, we tested participants with mTBI using a gap saccade task. Because this task manipulates the temporal gap between the offset of the fixation target and the appearance of the peripheral saccade target, it isolates the contribution of the disengagement process to saccadic reaction time. We found that participants with mTBI had significantly longer saccadic reaction times than controls when the temporal gap was short but not when it was long. This gap-dependent difference in saccadic reaction time was present within 2 days of the injury and resolved within 1 week. This pattern of results suggests that as the contribution of the disengagement process is reduced, so too is the extent of the reaction time deficit in the participants with mTBI. Taken together, this is consistent with the idea that the deficits in orienting visuospatial attention in participants with mTBI are fully accounted for by difficulties with the initial disengagement process.