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.

Grant Number: 5UG3EB036035-02
NIH Institute/Center: NIH
Principal Investigator: David Boas