But for the comparison between PHA and functional amnesia to be most meaningful, we need to know that they share underlying processes. One way to test this is to identify the brain activity patterns associated with PHA. In a groundbreaking study published in Neuron, neuroscientist Avi Mendelsohn and colleagues at the Weizmann Institute in Israel did just that using functional magnetic resonance imaging (fMRI). They carefully selected 25 people to participate in their experiment. Although all were susceptible to hypnosis, earlier testing had shown that half could respond to a PHA suggestion (labelled “the PHA group”) and half could not (the “non-PHA group”). In the Study session of their experiment, participants watched a 45-minute movie. One week later, in the Test session, participants returned to the laboratory and were hypnotized while they lay within the fMRI scanner. During hypnosis, people in both the PHA and non-PHA groups received a suggestion to forget the movie until they heard a specific cancellation cue.
Evidence from randomized controlled trials indicates that hypnosis, relaxation, and meditation techniques can reduce anxiety, particularly that related to stressful situations, such as receiving chemotherapy (see box). They are also effective for insomnia, particularly when the techniques are integrated into a package of cognitive therapy (including, for example, sleep hygiene). A systematic review showed that hypnosis enhances the effects of cognitive behavioral therapy for conditions such as phobia, obesity, and anxiety.