Brain scans don't show any signs of abnormal brain activity during hypnosis.

That depends on what you consider "abnormal". The states appear to be the same kind of states that occur in "normal" functioning, but they appear out of the context that they normally appear in. For example, according to one study a person exposed to a painful stimulus and one acting out a hypnotic suggestion to feel pain show similar patterns of brain activation, but a person told to "imagine" feeling pain shows a different one.

In general, brain scans do tend to show a difference between hypnotized subjects and subjects asked to pretend to be hypnotized.

My interpretation of these results is that hypnosis consists of the conscious mind telling the perceptual systems to shut up and do what they're told.