In the Cognitive Neuroimaging Lab at the Beckman institute, we use light to measure brain activity. We shine hundreds of lasers into the brain and measure the intensity and delay of light coming out with photo-detectors. This is called Diffuse optical imaging, and our technique is called the event-related optical signal.
We can use the light we measure to make maps of brain activity. To do this we have to map each light source we measure into specific areas of the brain.
The path that light takes to get to a single detector from one of the sources is modeled based on understanding of the diffusion and scattering of light in the head. It takes the shape that we like to call a BANANA.
If I plot all of the bananas for one subject in one of our experiments, we get an interesting looking map of that subjects brain, or at least the parts that our light is able to shine on: Here are four of the banana brains: