These questions required a “yes” or “no” response. For Test 1, they were asked 40 questions about the content of the movie (for example, the actress knocked on her neighbor’s door on the way home) and 20 questions about the context in which they saw the movie (for instance, during the movie, the door to the study room was closed). 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.Īfter hypnosis, participants’ memories were tested twice while the fMRI scanner recorded their brain activity. One week later, in the Test session, participants returned to the laboratory and were hypnotized while they lay within the fMRI scanner. In the Study session of their experiment, participants watched a 45-minute movie. 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”). They carefully selected 25 people to participate in their experiment. 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). One way to test this is to identify the brain activity patterns associated with PHA. (In contrast, explicit memories are those we consciously have access to, such as remembering a childhood birthday or what you had for dinner last night.) And, as suddenly as they lost their memories, they can just as suddenly recover them.īut for the comparison between PHA and functional amnesia to be most meaningful, we need to know that they share underlying processes. For instance, they might unconsciously dial the phone number of a family member whom they can’t consciously recall. However, as in PHA, they might still show “ implicit” evidence of the forgotten events. Case reports of functional amnesia, for instance, describe men and women who, following a traumatic experience such as a violent sexual assault or the death of a loved one, are unable to remember part or all of their personal past. Researchers have used PHA as a laboratory analogue of functional amnesia because these conditions share several similar features. That makes it a useful tool for research. Rather, PHA reflects a temporary inability to retrieve information that is safely stored in memory. These last two features-the dissociation and reversibility-confirm that PHA is not the result of poor encoding of the memories or of normal forgetting, because the memories return as soon as PHA is cancelled. The forgetting is reversible-when the suggestion is cancelled, their memories come flooding back. High hypnotizable people with PHA typically show impaired explicit memory, or difficulty consciously recalling events or material targeted by the suggestion, and a dissociation between implicit and explicit memory, so that even though they can’t recall the forgotten information it continues to influence their behavior, thoughts and actions. Now a new study shows that this hypnotic state actually influences brain activity associated with memory. Hypnotists produce PHA by suggesting to a hypnotized person that after hypnosis he will forget particular things until he receives a “cancellation,” such as “Now you can remember everything.” PHA typically only happens when it is specifically suggested and it is much more likely to occur in those with high levels of hypnotic ability, or “high hypnotizable” people. A classic example of this approach uses a technique known as posthypnotic amnesia (PHA) to model memory disorders such as functional amnesia, which involves a sudden memory loss typically due to some sort of psychological trauma (rather than to brain damage or disease). Hypnosis has long been considered a valuable technique for recreating and then studying puzzling psychological phenomena.
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