How To Read Brain Activity With Red Light

Hello! This is Andy. I’m about to tell you about something way cooler than implanting a chip in the brain to control robot arms, which is a very hard subject to top.

You can read brain activity by just shooting lasers into your skull and seeing how much of it comes back out. Introducing fNIRS, or functional near-infrared spectroscopy.

The basic principle of fNIRS is that blood changes shade as it becomes more oxygenated. Since deoxygenated blood absorbs more red light than oxygenated, it appears darker.

You can think of fNIRS as shining a flashlight onto the brain. Since groups of neurons firing will exhaust their blood supply, more active regions of the brain will have less oxygenated blood. By picking a laser in the right dark-red region, we can shoot it at brain tissue and look at how it scatters. By the Law of Large Numbers, some of the photons we inject will bounce back from the brain and make it out to a sensitive photodetector we placed near the laser source. Depending on how much of the brain in that region was active, we’ll see greater or fewer numbers of photons coming back out.

Regions of higher photon density in the namesake “banana” path

From there, there’s a few ways to go about getting blood activity, all of them specialized and requiring lots of electronics. But that’s it! fNIRS works, and it has been used in determining brain activity for…