Behaviour Research and Therapy 40 (2002) 995–1002 www.elsevier.com/locate/brat The nature of intrusive memories after trauma: the warning signal hypothesis Anke Ehlers a,* , Ann Hackmann b , Regina Steil b , Sue Clohessy b , Kerstin Wenninger b , Heike Winter b a Department of Psychology, Institute of Psychiatry, King’s College London, De Crespigny Park, London SE5 8AF, UK b Department of Psychiatry, Oxford University, Oxford, UK Accepted 11 July 2001 Abstract Individuals who had experienced a range of different traumas were asked to describe the quality and content of their intrusive memories. Visual intrusions were the most common, and thoughts were uncom- mon. Intrusion quality varied little with type of trauma. Intrusive memories commonly consisted of stimuli that were present immediately before the traumatic event happened or shortly before the moments that had the largest emotional impact (i.e., when the meaning of the event became more traumatic). It is suggested that intrusive memories are about stimuli that through temporal association with the trauma acquired the status of warning signals, i.e., stimuli that if encountered again would indicate impending danger. This explains why intrusive memories are accompanied by a sense of serious current threat. The warning signal hypothesis may be useful in guiding therapists in identifying the moments with the largest emotional impact that will need reprocessing in treatment, and in educating patients about the nature of reexperiencing symptoms.  2002 Elsevier Science Ltd. All rights reserved. Although intrusive memories are a core symptom of posttraumatic stress disorder (PTSD), relatively little is known about their nature and content (for reviews, see Reynolds & Brewin 1998, 1999). Preliminary research suggested that intrusive memories mainly consist of sensory fragments of the traumatic experience (Ehlers & Steil, 1995; Mellman & Davis, 1985; Van der Kolk & Fisler, 1995). It remains as yet unclear which of the sensory impressions from a trauma will be reexperienced. One hypothesis is that the most traumatic aspects of the event should be remembered best, e.g., somatosensory sensations when assaulted. In line with this hypothesis, * Corresponding author. Tel.: +44-20-7848-5032; fax: +44-20-7848-0591. E-mail address: a.ehlers@iop.kcl.ac.uk (A. Ehlers). 0005-7967/02/$ - see front matter  2002 Elsevier Science Ltd. All rights reserved. PII:S0005-7967(01)00077-8