We evaluate the feasibility of using functional near-infrared spectroscopy (fNIRS) to detect the neural correlates of conscious processing with one patient in the intensive care unit and 25 healthy controls. 

Little is known about the extent of covert cognitive processing in unresponsive critically ill patients. Advanced neuroimaging techniques offer new ways of enhancing our understanding of brain function in this population by providing objective and quantifiable markers of neural activity. fNIRS is a promising modality for this application since the technology is portable, inexpensive, and susceptible to motion, making it ideal for the intensive care environment. 

A series of validated neuroimaging paradigms were employed to assess somatosensory perception, auditory processing, and covert command following in a behaviourally unresponsive patient who sustained a brainstem stroke and with 25 healthy controls. An fNIRS system with 129 channels providing full head coverage was used. A channel was considered activated if there was a significant concurrent increase in oxyhemoglobin and decrease in deoxyhemoglobin (p<0.05). 

For the somatosensory perception task, 100% of healthy controls showed activity in somatosensory areas. 88% of healthy participants demonstrated responses in the superior and medial temporal gyrus in response to the auditory processing task, while 92% of healthy participants had responses to the motor imagery task. When employed in the ICU with one patent, fNIRS activity revealed preserved somatosensory and auditory processing abilities. Moreover, the patient was able to reliably and consistently perform the motor imagery task, demonstrating preserved conscious awareness despite being behaviourally unresponsive. 

This work demonstrates the feasibility of using fNIRS as an assessment tool for covert cognitive function in the ICU.  Future research will focus on evaluating the diagnostic and prognostic efficacy of fNIRS with acute critically ill patients.