New psychology research finds Pavlovian threat conditioning can induce long-lasting memory intrusions

Pavlovian threat conditioning (also known as fear conditioning) is a basic form of learning in which an animal or person comes to associate a particular stimulus with a negative outcome. New research, published in Behaviour Research and Therapy, indicates that this type of conditioning can generate intrusive memories that persist over time.

The findings provide insight into the development of posttraumatic stress disorder (PTSD), and could have important implications for both research on learning and clinical treatment.

“I am very interested in investigating if the way we interact with each other after a trauma can increase or decrease the risk of developing symptoms of PTSD,” said study author Lisa Espinosa, PhD student and member of the Emotion Lab at the Karolinska Institute.

“Key symptoms of PTSD are intrusive memories, which are involuntary as well as intrusive images or sounds of an event. They pop into your mind without you wanting them to. Knowing if the type of interactions we have after trauma influences the development of symptoms such as intrusive memories would facilitate the development of clinical interventions directly after trauma, and decrease the risk of people developing symptoms in the first place.”

The study included a final sample of 81 adults. Participants visited a laboratory where they were repeatedly shown two different emotionally-neutral images (such as a tray of buttons). To induce a conditioned threat response, one of the images was followed by an unpleasant electric shock during four of the six presentations.

Participants were then given a three to four minute break, and were randomized to either experience a supportive social interaction, an unsupportive social interaction, or no social interaction. The participants were then shown the same two images, nine times each, without receiving any shocks.

For the next seven days, the participants used an internet-based diary to report occurrences of intrusive memories of the images. On the eighth day, they returned to the laboratory room and were exposed to the images again. During the study, the researchers measured the participants’ skin conductance response, also known as the electrodermal response, to assess their physiological arousal.

Espinosa and her colleagues found that the image that had been paired with an electric shock tended to generate more intrusive memories, compared to the image that had not been paired with an electric shock. The finding provides evidence of a link between conditioned threat responses and intrusive memories.

“When you have a negative experience (e.g. a car accident or an assault), you might experience intrusive memories of what happened,” Espinosa told PsyPost. It’s important to know that these intrusions don’t have to be of a threatening or negative aspect of what happened (e.g. a knife or blood) in order to be distressing or negatively affect your life. They could instead include neutral objects or sounds that are associated with the negative experience (e.g. a color or the sound of the rain).”

“The content of the intrusions might be benign per se but their meaning and the reactions you have when they pop into your mind are intrusive,” Espinosa explained. “In our study, participants developed intrusive memories of pictures of a clock or an umbrella because they were associated with mild electric shocks. They learned that a (previously) neutral object is associated with a negative experience and therefore reacted more physiologically when exposed to these pictures (they sweated more) and had more intrusive memories of these images during the following 7 days.”

A follow-up survey completed by 59 of the 81 original participants provided evidence that the intrusive memories could persist for up to a year. This was particularly true among participants who had a greater number of previous traumatic experiences and higher trait anxiety.

But could a supportive social interaction help buffer against intrusive memories? The researchers found no evidence that this was the case.

“Receiving social support during a negative experience has been shown to decrease stress responses to that event (i.e. lower blood pressure and slower heart rate),” Espinosa said. “Social support is especially helpful when it’s given by someone close to you such as a close friend or a family member. But unfortunately we rarely experience a traumatic event with a calm friend by our side. Therefore, in our study we tried to test whether receiving support given by a stranger after a negative experience would help decrease stress responses and the number of intrusive memories.”

“We wanted to test the type of interactions that could take place with the hospital staff in the waiting room of a hospital directly after a traumatic event. After receiving mild electric shocks to neutral images, we gave our participants either a very supportive interaction (e.g information about what was going on, eye contact, asking how they felt), an unsupportive interaction (giving no or unclear information on what was going on, avoiding eye contact, entering the room without asking any questions or showing any concern) or not interacting with them (our control group).”

“We predicted that a supportive interaction would decrease the number of intrusions and an unsupportive interaction would increase the number of intrusions participants would have,” Espinosa explained. “Unfortunately, we did not find an effect of our support manipulation. This suggests that studying social support is tricky and to understand its potential benefit on post-trauma recovery, we need to continue investigating the exact type of social support needed to decrease the risk of developing intrusive memories.”

The authors noted that one of their study’s limitations is its ecological validity, or the extent to which their testing environments represented real-world experiences. Nevertheless, the findings help shed light on fundamental aspects of cognition, which could lead to improved treatments for individuals struggling with traumatic memories.

“This is an experimental study in a very controlled environment (a laboratory) with electric shocks as analogue for a traumatic experience,” Espinosa told PsyPost. “Using such settings to know about actual interactions after real-life trauma probably sounds like a bit of a stretch. We can’t draw big conclusions, but we move one step closer to understanding what is happening and what might work. It is important to know that it is by first testing hypotheses in a controlled environment that we can find what could work in order to develop evidence based interventions. Only interventions that are thoroughly experimentally tested should be used with vulnerable populations, such as trauma victims.”

The study, “Pavlovian threat conditioning can generate intrusive memories that persist over time“, was authored by Lisa Espinosa, Michael B. Bonsall, Nina Becker, Emily A. Holmes, and Andreas Olsson.