Towards Neuroscience in the Everyday World: Progress in wearable fNIRS instrumentation and applications Alexander von Lühmann 1,2,* , Bernhard B. Zimmermann 1 , Antonio Ortega-Martinez 1 , Nathan Perkins 1 , Meryem A. Yücel 1,2 , David A. Boas 1,2 1 Neurophotonics Center, Biomedical Engineering, Boston University, Boston, MA 02215, USA 2 Athinoula A. Martinos Center for Biomedical Imaging, Department of Radiology, Massachusetts General Hospital, Harvard Medical School, Charlestown, MA 02129, USA *Corresponding author. Email: avolu@bu.edu Abstract: Wearables and machine learning have opened up a new field of research, the Neuroscience of the Everyday World. We present our recent contributions to fNIRS instrumentation (ninjaNirs and ninjaCap) and multimodal analysis (BLISSA 2 RD and GLM with tCCA). © 2020 The Author(s) 1. Motivation Neuroimaging techniques used in contemporary neuroscience research provide great insights into the healthy functioning brain and have led to many advances in characterizing, diagnosing and in developing potential targeted interventions for brain disorder. However, there is still a big gap in our understanding of both healthy and impaired brain function. Part of the reason for this stymied progress is that while we have some understanding of how the brain functions in single-snapshot experiments under restricted lab settings, we do not know how it works in dynamic, complex and multisensory real-world environments – a new field of research that we term the Neuroscience of the Everyday World (NEW). Solving this complex problem requires enabling technologies to continuously track and analyze human brain function and behavior. We present our vision and recent contributions towards wearable neuroimaging instrumentation and multimodal signal analysis: Our wearable open functional Near Infrared Spectroscopy (fNIRS) neuroimaging platform, the ninjaNIRS and ninjaCap, and novel multimodal fNIRS analysis approaches for improved separation of evoked hemodynamic signals and systemic physiology. 2. Recent Progress in Instrumentation and Processing Wearable neuroimaging: M3BA, ninjaNIRS and ninjaCap An increasing number of novel fiber less and lightweight wearable fNIRS instruments have been published in recent years [1]. This trend, similarly observable for Electroencephalography (EEG), makes both modalities suitable for Neuroimaging in the Everyday World. We have previously developed M3BA, a Mobile, Modular, Multimodal Biosignal Acquisition architecture, for the localized simultaneous hybrid acquisition of fNIRS, EEG and other biosignals [2]. With greatly reduced intermodality crosstalk and high timing precision, the wireless modules provide a scalable stand-alone architecture for high-performance measurements with a low numbers of channels. For whole head imaging, we have recently developed and are disseminating a wearable, fully scalable and modular open source fNIRS system (see Figure 1, left) that we named ninjaNIRS [3]. It is based on a new compact optode, that consists of one dual wavelength LED (730/850 nm) and one photodiode on a miniaturized printed circuit board that also incorporates a trans-impedance amplifier, analog-to-digital converter, a field programmable gate array (FPGA), and an inertial monitoring unit. The optode acts both as short-separation detector and as longer separation detector for surrounding optodes and has a noise equivalent power of less than 500 fW/√Hz at 730 nm and a dynamic range of almost 140 dB. The system is functional with as little as 2 optodes and can easily be expanded to as many as 128 optodes. We have developed a process to generate completely customizable and individualized flexible head caps, which we named ninjaCap, using 3D printing of flexible materials and our established brain atlas software AtlasViewer [4] for mapping of fNIRS optodes and EEG electrode positions to the brain surface. The approach Figure 1: ninjaNIRS optodes and controller (left) and multimodal extension of the General Linear Model with tCCA.