Kosslyn SM, Thompson, WL, Spiegel D, et al. Am J Psychiatry 2000;157:1279-84

This is the data that I’m going to walk you through. We’re graphing here the regional cortical blood flow in this part of the color association region in the left cortex, and this is the amount of blood flow in an individual, individuals not being hypnotized or hypnotized. Without hypnosis, people who are seeing gray and told to see gray had this basal level of blood flow in that color region. … If they were seeing gray and told to see color, it didn’t change. They knew they were not seeing color. If they were seeing color, whether or not they were told it was color or gray, they had a higher level of blood flow appropriate for color vision.

What happens now with hypnosis? If you’re seeing gray and you’re told you see in color, the blood flow went up to that of the level of color perception; and if you’re seeing color and you’re told, under hypnosis you are to see color, the level went up even further. This suggests that the brain is acting as if what you’re told to see is what you’re seeing.