Expanding Inclusion of All Subjects for Ultra-High Density Wearable fNIRS in the Everyday World

Abstract There is a great need to enable scientists to link brain activity to human movement, perception and cognition, and social communication and interaction continuously, in real time, and in naturalistic settings. Such tools will provide profound new insights into not only how the healthy brain works, but also when and why breakdowns occur in movement, perception/cognition, and communication. While fMRI is providing greater understanding of how the brain functions in restricted lab settings, we do not know how it works in dynamic, complex and multisensory real- world environments. To push this important work forward, we are actively advancing high density (HD) wearable functional Near Infrared Spectroscopy (fNIRS) systems to permit continuous tracking of human brain function and behavior in real time to understand how a healthy brain works and how and when failures in simple human actions occur. Here, we are addressing an old and a new challenge in fNIRS measurements. The old challenge relates to improving the sensitivity of fNIRS measurements to overcome the issues with hair characteristics and skin tone that reduces the signal-to-noise ratio and compromises inclusion of all subjects in fNIRS studies. The new challenge arises as the field develops wearable fNIRS systems and pushes for ultra- high density (UHD) measurements with more overlapping channels to further improve spatial resolution and sensitivity to achieve comparable performance in the cortex as compared to fMRI, but making it challenging to maintain wearability. We will achieve a 5x improvement in detector signal to noise ratio to benefit all subjects and increase LED peak powers to increase signal to noise ratio up to 100x in subjects with the most attenuating hair and skin characteristics. We will achieve another 10x improvement in image contrast to noise ratio afforded by the increased numbers of overlapping measurements with UHD fNIRS versus HD fNIRS. We will also complete a demonstrative study of our impact on enabling real-world studies of brain function inclusive of diverse human subjects, by investigating the impact of mental workload on spatial navigation.