Table 1.

Brief literature review.

References	Methods	Results
Gemignani et al. (2018)	Performed a linear mixed effect model with hair as a fixed effect.	Model accuracy for deoxyHb using the generalized linear model GLM) was significantly higher for blonde subjects when compared to brown-haired subjects.
Nagels-Coune et al. (2020)	Studied how certain characteristics of hair (thickness, root density, and color) impact fNIRS results using a suitability questionnaire.	Subjects with lower suitability scores (based on hair/skin color) generally had more channels with poor signal-to-noise ratio.
Fang et al. (2018)	Used Monte Carlo simulation to study light propagation using a visible Chinese human corpse cryosection dataset.	Detected light intensity signal decreased by 15–80% when scalp hair follicle density varied from 1–11%.
Bronkhorst et al. (2019)	Studied how a simple head maneuver redistributed cerebral blood volume to verify if photon transmission is sufficient in darker-skinned subjects. They compared effects of a head tilt in a pigmented vs. non-pigmented subject.	Data from a pigmented and non-pigmented had comparable Hb patterns to effects of the head tilt. This tilt is recommended as a test to confirm photon transmission in subjects with pigmented skin.