Hypnotic hues in the brain

Hypnosis uniquely colors the activity of brain areas involved in visual perception, a new study finds. This result supports the view that hypnotized people enter a distinct psychological state rather than, as some scientists propose, only play a role designed to please the hypnotist.

A team led by psychologist Stephen M. Kosslyn of Harvard University took positron emission tomography (PET) scans of the brains of eight adults as they viewed a pattern of rectangles shown either in various colors or shades of gray. Participants, ages 20 to 35, completed a set of four tasks, once while hypnotized and once in an alert state. Researchers told the subjects to see the two patterns as they appeared, to imagine adding color to the gray image, and to imagine draining the bright hues out of the colored one.

A left-brain area known to contribute to color processing displayed the sharpest increases in blood flow—a sign of greater neural activity—among hypnotized participants as they observed imaginary colors, Kosslyn’s group reports in the August American Journal of Psychiatry.

The same area showed the greatest decreases when hypnotized participants imagined colors as grays. This region specifically contributes to the hypnotic state, the team suggests. In contrast, a right-brain area that also influences color processing showed a marked blood-flow surge as both hypnotized and nonhypnotized viewers imagined seeing colors and a drop as they envisioned grays. This region fosters mental imagery, the team theorizes.