fNIRS for Disorders of Consciousness

The goal of this observational study is to learn whether functional near-infrared spectroscopy (fNIRS) can measure brain activity in healthy adults and in people with disorders of consciousness (DoC) in the neuro-intensive care unit (Neuro-ICU). DoC include conditions such as coma and minimally conscious state that occur after severe brain injury. These conditions make it difficult to assess a person's level of awareness because many clinical tests rely on observable behaviors such as speaking or moving, which are commonly impaired after brain injury. The main questions the study aims to answer are: * Can fNIRS detect changes in brain activity in healthy adults when they receive sensory stimulation or perform mental tasks? * Can the same fNIRS protocol be used in patients with disorders of consciousness in the Neuro-ICU to measure brain responses and determine whether the method is feasible in this clinical setting? The investigators will first study healthy adult volunteers to establish baseline brain responses and determine which tasks produce the most reliable signals. The protocol will then be applied to patients with disorders of consciousness admitted to the Neuro-ICU. Participants will take part in a single research session lasting about 30 to 45 minutes while wearing the lightweight fNIRS headband that measures brain oxygen levels using near-infrared light. During the session, participants will: * Wear a non-invasive fNIRS headband placed on the forehead * Receive gentle sensory stimulation (for example, compression devices on the legs or hands) * Listen to sounds or spoken sentences * Perform guided mental tasks such as imagining walking through their home or imagining moving a limb The study does not test a treatment and will not change medical care. The goal is to determine whether fNIRS can safely and reliably measure brain activity at the bedside and provide preliminary information that may help guide future research on improving the assessment of consciousness after brain injury.