Table 2.

Studies with mobile NIRS devices.

MOBILE NIRS STUDIES
Authors	Area of interest	NIRS set-up	External validity	N	Method	Results
Bozkurt et al., 2005	New-born brain metabolism	Validity of the system	Relatively high external validity	1 (new-born) and prior phantom tests	NIRS prototype of a low-cost, battery-operated, dual wavelength, continuous wave	Shot-limited SNR of 67 dB for 10 Hz temporal resolution was achieved. Reliable clinical tool employed at bedside
Muehlemann et al., 2008	Tissue oxygenation and cortical hemodynamic response to sensory stimuli	Wireless NIRI device tested in a solid silicone phantom and an in-vivo experiment (4 sources, 4 detectors)	Very low external validity	1 phantom test and 1 male (in-vivo experiment)	In-vivo experiment: baseline; pneumatic pressure cuff attached to the upper arm	Tests with lightweight and inexpensive miniaturized wireless NIRI device show that the measurement accuracy is comparable to well-established instruments
Atsumori et al., 2009	Pre-frontal cortex while subject performed a word-fluency task	Functional wearable NIRS brain imaging with a prototype during reading	High external validity (but computer task)	1 (adult)	During the task periods, the subject was asked to think of as many words as possible that begin with the Japanese character	Typical changes in oxy-Hb and deoxy-Hb during the task. Therefore, prototype can be used to investigate functions in the prefrontal cortex
Yoshino et al., 2013a	Frontal lobe activations during car acceleration and deceleration	Functional wireless multi-channel system (FOIRE-3000, Shimadzu); 16 sources and 16 detection probes	Very high external validity (field experiment under specific driving conditions)	12 (adults)	Acceleration and deceleration	Results show that vehicle deceleration requires more brain activation, focused in the prefrontal cortex, than does acceleration
Yoshino et al., 2013b	Activation in the frontal lobe during driving operations	Functional wireless multi-channel system (FOIRE-3000, Shimadzu); 16 sources and 16 detection probes	Very high external validity (field experiment under specific driving conditions)	12 (adults)	Resting state, acceleration, deceleration, U-turn, stop	Powerful technique for investigating brain activations outdoors, proving to be sufficiently robust for use in an actual highway driving experiment in the field of intelligent transport systems
Piper et al., 2014	Motor cortex activity during bicycling (left hand gripping)	Functional wireless and mobile NIRS brain imaging during an outdoor activity	Very high external validity (field experiment with specific task conditions)	8 (adults)	Three different exercise conditions: (1) during outdoor bicycle riding; (2) while pedaling on a stationary exercise bicycle; (3) sitting still on a stationary exercise bicycle	Following left hand gripping, a significant decrease in the deoxy-hemoglobin concentration over the contralateral motor cortex could be found for all three conditions; outdoor and indoor conditions showed no significant difference in the shape or amplitude of HbR.
Holper et al., 2014	Simultaneous comparison with EDA; activity of lateral prefrontal cortex during risky decisions	Functional wireless and mobile NIRS brain imaging NIRS machinery with only one light-source	Relatively high external validity (but computer task)	20 (adults)	Risky decision-making task (Christopoulos et al., 2009; Tobler et al., 2009) and baseline recording	Enhanced activation in the lateral prefrontal cortex is related to high-risk decisions; reduced activation in this area is related to low-risk decisions. EDA revealed increasing responses for high-risk decisions