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.

Functional near-infrared spectroscopy (fNIRS) is a non-invasive neuroimaging method that measures changes in oxygenated (HbO) and deoxygenated hemoglobin (HbR) in cortical tissue. Through neurovascular coupling, neural activity in specific brain regions is associated with increased metabolic demand and localized changes in cerebral blood flow, resulting in measurable shifts in HbO and HbR concentrations. These changes form the basis of the blood oxygen level-dependent (BOLD) signal measured in functional magnetic resonance imaging (fMRI) and the optical signals detected by fNIRS.

Assessing level of consciousness in patients with severe brain injury remains a clinical challenge. Standard bedside assessments rely primarily on observable behaviors such as eye movements, motor responses, or verbal output. When these behaviors are impaired by brain injury, observable behavior may not accurately represent preserved cognition. Functional neuroimaging studies have demonstrated that some individuals diagnosed with disorders of consciousness (DoC) can generate brain responses during cognitive tasks even when behavioral responses are absent. However, many neuroimaging methods, particularly fMRI, are difficult to implement in critically ill patients because they require specialized facilities and patient transport outside the intensive care unit. fNIRS provides a portable, bedside method for measuring hemodynamic responses associated with neural activity, making it potentially suitable for use in the neuro-intensive care unit.

This study is a non-therapeutic observational pilot investigation designed to evaluate fNIRS signal responses and the feasibility of implementing a structured cognitive paradigm during bedside monitoring. The study is conducted in two stages.

In the first stage, the protocol is implemented in healthy adult participants to characterize the magnitude and consistency of fNIRS responses during a series of sensory and cognitive paradigms. These data establish baseline response patterns and help identify task conditions that produce reliable hemodynamic signals.

In the second stage, the refined protocol is implemented in patients with DoC in the neuro-intensive care unit to evaluate feasibility and obtain preliminary observations of cortical hemodynamic responses in this population.

During fNIRS monitoring, participants are exposed to a series of paradigms designed to engage different levels of sensory and cognitive processing. These include somatosensory stimulation, auditory processing tasks, semantic language processing, spatial navigation imagery, and motor imagery. Tasks are presented in a block design with alternating task and rest periods to allow detection of hemodynamic changes associated with neural activation.

The goal of this pilot study is to determine whether bedside fNIRS monitoring can produce reliable hemodynamic signals during these paradigms and whether the protocol can be feasibly implemented in a Neuro-ICU environment. Findings from this study will provide preliminary data to inform future research on objective methods for assessing brain activity in patients with DoC.