Study population: This study will recruit 50 active duty service members and veterans with a documented TBI to participate in one of two study groups. The insomnia group (n=25) will include participants that have a current clinical diagnosis of insomnia without obstructive sleep apnea. The no-insomnia group (n=25) will include participants with no current clinical diagnosis of insomnia or obstructive sleep apnea. Withdrawals/dropouts will be replaced to obtain 20 participants per group who complete the study.