There is at least one 'affordable' fNIRS device coming to market that looks promising, https://foc.us/fnirs-sensor/ https://foc.us/fnirs-sensor/ There's a paper

There is at least one 'affordable' fNIRS device coming to market that looks promising, https://foc.us/fnirs-sensor/ https://foc.us/fnirs-sensor/ There's a paper somewhere on using machine learning to help identify signal, this one is specifically about pain, https://www.nature.com/articles/s41598-019-42098-w https://www.nature.com/articles/s41598-019-42098-w Say for example you were making an insurance claim for neuropathic pain, this kind of information could be very important.