Abstract: Systems and techniques for detecting and monitoring for traumatic brain injury and recovery are described. A system can include a photoplethysmography (PPG) system with a robust PPG sensor and a monitoring system with a detection and monitoring module. The detection and monitoring module, when executed, directs the monitoring system to: extract a pulse rate waveform from a signal from the PPG system containing information about a patient's heart; determine a pulse rate variability for the pulse rate waveform; and compare the pulse rate variability to a reference to determine a brain injury status.