Described herein are fNIR-based brain computer interfaces. Training of individuals to intentionally control neural activity in specific cortical areas, thereby up-regulating and down-regulating oxygenation levels in specific locations in the brain is also provided herein. Further, continuous and/or binary control over computing environments using fNIR brain computer interfaces. Further still, a scale for brain interface index for oxygenation of a portion of the brain is provided herein.