A hypnotic paradigm for studying intrusive memories Zoe Hill, Lynette Hung, Richard A. Bryant * School of Psychology, University of New South Wales, Sydney, NSW 2052, Australia article info Article history: Received 25 April 2009 Received in revised form 24 April 2010 Accepted 4 May 2010 Keywords: Intrusions Hypnosis Unwanted thoughts abstract Despite the importance of intrusive memories in clinical disorders, research has been limited by a dearth of paradigms that permit experimental study of intrusions. This study describes a hypnotic paradigm for eliciting intrusive memories. Forty-nine highly hypnotisable participants nominated a distressing memory prior to being hypnotised. During hypnosis, they received the suggestion that they would remember the memory in response to a designated cue after the hypnosis session. Half of the partici- pants also received a posthypnotic amnesia suggestion for the source of the memory. Following hypnosis, all participants completed a cognitive task and during the task received the cue to recall the memory. Results demonstrated that memories experienced after posthypnotic amnesia were experienced as more involuntary and more distressing than those that were knowingly retrieved. Participants in the post- hypnotic amnesia condition also demonstrated greater interference on the cognitive task after the retrieval cue was given than those who intentionally retrieved the memory. These findings suggest that posthypnotic suggestion provides a useful paradigm to elicit intrusive memories under experimental conditions. Ó 2010 Elsevier Ltd. All rights reserved. Intrusive thoughts and memories are common in many clinical disorders, including posttraumatic stress disorder (Brewin, 1998), obsessive compulsive disorder (Salkovskis, 1985), depression (Brewin, 1998), social phobia (Hackmann, Clark, & McManus, 2000), and agoraphobia (Day, Holmes, & Hackmann, 2004). Across all these disorders, intrusions share the common properties of occur- ring involuntarily and causing significant distress (Clark & Rhyno, 2005). In general, intrusive memories are experienced as more vivid and distressing than non-intrusive memories (Berntsen, Willert, & Rubin, 2003). They are also experienced as sponta- neous, repetitive, and difficult to control, regardless of the content (Clark & Rhyno, 2005; Dougall, Craig, & Baum, 1999). Since the early proposals of Janet (1904), theorists have asserted that intrusive memories of trauma are different from ordinary autobiographical memories (e.g., Brewin, Dagleish, & Joseph, 1996; Ehlers & Clark, 2000). Such memories have been described as being more vivid and more emotionally intense than voluntary memories of trau- matic or non-traumatic events (Bryant & Harvey, 1998). Intrusive memories have also been shown to be difficult to control (Wegner, 1994), and to interfere with ongoing task performance (Hellawell & Brewin, 2002). Most research has relied on retrospective reports of intrusive memories (e.g., Brewin, 1998; Bywaters, Andrade, & Turpin, 2004; Hackmann, Ehlers, Speckens, & Clark, 2004; Reynolds & Brewin, 1998) or diary methods (e.g., Berntsen, 2001). Other studies have studied intrusions by presenting partic- ipantsS200 with evocative stimuli (Lynch, Schneider, Rosenthal, & Cheavens, 2007) or reminders of traumatic events (Bryant & Harvey, 1998). All of these approaches are potentially confounded by retrospective bias or by extraneous environmental factors (Clark & Purdon, 1995). There is a need to develop new paradigms to examine intrusions under experimental conditions. There are several reasons to suggest that hypnosis may provide a useful model for studying intrusions. Hypnotisability is associated with susceptibility to intrusive thoughts (Bryant & Idey, 2001) and a tendency to attribute involuntariness to internal experiences (Kirsch & Lynn, 1999). Numerous clinical disorders that are char- acterised by intrusive memories are associated with elevated levels of hypnotisability, including PTSD (Spiegel, Hunt, & Dondershine, 1988), acute stress disorder (Bryant, Guthrie, Moulds, Nixon, & Felmingham, 2003), and phobias (Frankel & Orne, 1976). One of the classic responses during hypnosis is posthypnotic amnesia. Posthypnotic amnesia involves suggesting to hypnotised persons that following hypnosis they will be unable to recall particular aspects of the hypnotic experience until they receive a cancellation instruction. A number of studies have demonstrated that a suggestion for posthypnotic amnesia can alter an individual’s access to autobiographical memories to create profound but reversible forgetting in highly hypnotisable individuals (Barnier, 2002; Bryant, Barnier, Mallard, & Tibbits, 1999). More usefully, posthypnotic amnesia has often been shown to be a useful means of * Corresponding author. Tel.: þ61 2 93853640; fax: þ61 2 93853641. E-mail address: r.bryant@unsw.edu.au (R.A. Bryant). Contents lists available at ScienceDirect Journal of Behavior Therapy and Experimental Psychiatry journal homepage: www.elsevier.com/locate/jbtep 0005-7916/$ e see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.jbtep.2010.05.001 J. Behav. Ther. & Exp. Psychiat. 41 (2010) 433e437