Whether or not you believe in hypnosis, neuroscientists are now showing that the practice does indeed produce measurable effects in the brain.
For example, in 2006, researchers in Germany found that subjects under hypnosis experienced a significant reduction in pain sensitivity when exposed to an agonizing thermal stimuli. Using functional magnetic resonance imaging, the researchers also discovered that pain reduction in hypnotized subjects was coupled with distinctly different brain activity compared to un-hypnotized subjects who were administered the same painful heat.
"The major finding from our study... is that we see reduced activity in areas of the pain network and increased activity in other areas of the brain under hypnosis," Dr. Sebastian Schulz-Stubner said.
In another study, hypnotized subjects were told that they would see photos in color, but were then presented with photos in gray-scale. Despite the visual trickery, the regions of the brain associated with color processing were still activated.
In the vast majority of these types of studies, researchers noted that hypnosis' effects on the brain were most plainly seen in subjects deemed "highly suggestible." To skeptics (like myself) this means that these "highly suggestible" volunteers were simply the sort of people who believe in wonky things, like hypnosis. So, when they were supposedly hypnotized, they were really under a self-induced placebo effect.
However, a 2004 study conducted by researchers at the University of Virginia revealed that subjects prone to be hypnotized actually had structural differences within their brains. In the study, highly hypnotizable subjects, on average, sported a 31.8% larger rostrum, a part of the brain involved in the allocation of attention and transfer of information between prefrontal cortices.
You don't have to believe in hypnosis, but scientific research does indicate that all of those mesmerizing spirals, swaying pocket-watches, and showy hypnotists are capable of delivering measurable changes in the human mind