The purpose of this research study is to test the effectiveness of virtual reality (VR) based treadmill training on walking ability. The study will also help to understand the changes in cognitive ability and brain activity as a result of VR-based treadmill training after a brain injury. The study will include 3 groups: C-MILL training group (CTG), Treadmill training group (TTG), and healthy control group (HCG). Individuals with brain injury will be randomly assigned to C-MILL training group, or Treadmill training group. The CTG and TTG will participate in up to 13 sessions. The participants will be screened for the inclusion/exclusion criteria and consented during the first session. They will participate in two data collection sessions, one before the training and one after the training. The participants will undergo 10 training sessions. Individuals in the CTG will receive gait and balance training sessions with the virtual reality and auditory cues using C-MILL (such as walking on a pathway, obstacle avoidance, lateral balance etc.) to provide task specific training. C-Mill (Motekforce Link, Amsterdam, The Netherlands) is an instrumented treadmill that uses visual (on the screen as well on the treadmill) and acoustic cues for gait and balance training. The C-Mill allows for gait and balance adaptability strategy as it can provide obstacle avoidance environments, change in speed and various walking pathways in a safe and controlled environment. Individuals in TTG group will walk on the treadmill (C-MILL) or stand on the treadmill (C-MILL) with no visual or auditory cues. HCG will participate in up to four sessions. The participants will be screened for the inclusion/exclusion criteria and consented during the first session. They will participate in two data collection sessions and one C-MILLsession. Each training session will last for 45 minutes. During the 45 minutes, the participants will perform the task for approximately 1 minute. Participants will be allowed as much rest as needed by them. During the training all participants will wear the safety harness to protect from falling. In addition spotter will be present with the participants to prevent falls. Data Collection: Each participant's baseline and follow up data will be collected for a) functional b) neuromechanical c) cortical and d) cognitive outcomes. During walking on treadmill data will also be collected with instrumented C- MILL. C-MILL can provide gait parameters such as step length, width, frequency, speed and symmetry in addition to center of pressure for evaluation of gait and balance. During Training Sessions: The instrumented treadmill will collect force data during training.