From hemodynamics to function: the role of fNIRS and hybrid EEG-fNIRS systems in next-generation assistive technologies for rehabilitation

Assistive technologies (AT) serve as fundamental tools for rehabilitation because they help people with neurological or physical disabilities to restore their abilities, independence and their overall life satisfaction. Existing AT control methods, which include manual operation, eye tracking, voice commands, electromyography (EMG) and electroencephalography (EEG), have improved rehabilitation results but still face challenges because of their inability to maintain reliable performance during user exhaustion and difficulties operating in challenging situations. Functional near-infrared spectroscopy (fNIRS) has recently become a new neuroimaging technique that provides excellent imaging capability, can be used while moving, and has portable design features. fNIRS-based devices such as wheelchairs, robotic prostheses, and brain-computer interfaces (BCIs) have proven their ability to decode user intention and assist rehabilitation. The limited ability of fNIRS to measure time intervals prevents its use in real-time systems. The hybrid EEG-fNIRS systems combine EEG technology, which provides high-speed temporal measurements, with fNIRS technology, which provides spatial and hemodynamic measurements. The multimodal techniques combine different measurement methods, which improve accuracy while decreasing false positive results and increasing system adaptability. This review critically examines how AT control modalities have been evolving, and it also measures what fNIRS can do technically, plus what it struggles with, and then it pulls together the available evidence on hybrid EEG-fNIRS systems as a possible way toward more adaptive, user-centered rehabilitation technologies.