Evaluation of Cognitive Function Using Time-Domain Optical Neuroimaging

Functional near-infrared spectroscopy (fNIRS) is a non-invasive optical neuroimaging technique that measures changes in the concentration of oxygenated and deoxygenated hemoglobin in the outer cortex of the brain. By detecting these changes, fNIRS provides a measure of neural activity associated with motor, emotional, perceptual, and cognitive brain processes. Recent advancements in system-on-a-chip optics have miniaturized ultrafast optical detectors and time-domain (TD)-fNIRS systems which capture the time-of-flight distribution of photons. The first wearable TD-fNIRS system featuring a high-density sensor array in a mobile headset form factor is Kernel Flow (Kernel Inc., Los Angeles, CA). The overall aim of this project was to evaluate the functional neuroimaging capabilities of this system through an investigation into the neural correlates of cognitive function. A comprehensive study was designed with five cognitive tasks that elicit well-characterized responses across various brain regions. These tasks probe several domains of cognition including problem solving, working memory, attention, response inhibition, and language. Healthy participants (n=15) volunteered for this study and completed these tasks while their brain activity and physiological responses were measured with the Kernel Flow system and a smart watch. The results agree with previous investigations of these cognitive tasks and domains of cognition. Significant increases in neural activity were primarily found in the prefrontal cortex when participants were performing problem solving, working memory, and response inhibition functions. The right inferior frontal gyrus in particular, well known for its role in attentional control, was active across tasks that required focused attention. Responses were also elicited in temporal cortices and occipital visual association areas in several tasks. Additional TD-fNIRS signal features and whole-head measurement provide opportunities for further investigations and potentially identify better characterization of brain processes. As the first cognitive study to use this system, it sets a foundation for the use of this technology in explorations of human cognition.