Summary: New research shows that when older memories are reactivated under stress, people are more likely to misinterpret safe situations as dangerous.
Source: UT Austin
Recognizing threats is a core function of the human mind, shaped in part by past negative experiences. However, when older memories are reactivated in the presence of stress, people can overgeneralize danger and treat harmless cues as threats, according to a study published in the Proceedings of the National Academy of Sciences.
Researchers from Dell Medical School at The University of Texas at Austin, New York University and McGill University examined how stress and the passage of time influence fear generalization — a central feature of anxiety and stress-related disorders such as post-traumatic stress disorder (PTSD).
“The human mind uses cues to danger learned over time for self-protection, but certain conditions can lead people to misidentify those cues,” said Joseph Dunsmoor, lead author and assistant professor of psychiatry at Dell Med. “Our findings show that stress combined with a delay after an adverse event increases the tendency to overgeneralize fear.”
Dunsmoor conducted the work while a postdoctoral researcher in Elizabeth Phelps’s lab at New York University. A. Ross Otto, now an assistant professor at McGill University, contributed to the study while working as a postdoc at NYU.
PTSD, which affects millions of adults each year, is characterized in part by an inability to distinguish threat from safety: everyday sounds or sights that resemble elements of a traumatic event can trigger intense fear. Understanding how memories and stress interact to produce these reactions helps researchers design better ways to prevent and treat such disorders.
“These results provide laboratory evidence for why PTSD symptoms often worsen during periods of stress, and how repeated stress or trauma in contexts like combat could increase vulnerability to PTSD,” said Suzannah Creech, associate professor of psychiatry at Dell Medical School, who was not involved in the study but works clinically with veterans recovering from trauma. “This knowledge may inform improved strategies for treatment and prevention.”
Study design and methods
The researchers tested healthy adult volunteers using a tone-based conditioning task. Participants heard two distinct tones: one tone (the conditioned stimulus) was paired with a mild electric shock to the wrist, calibrated by each participant to be “highly annoying but not painful”; the other tone was never followed by a shock. To measure generalization, the team later presented a range of intermediate tones that spanned the two original frequencies and assessed participants’ shock expectations and physiological arousal using skin conductance responses (SCRs), which index sympathetic arousal.
To manipulate stress, half of the participants completed an arm ice bath procedure designed to raise cortisol levels, while the other half completed a control arm bath with room-temperature water. The experiment used a between-subjects design with two timing conditions: one group performed the generalization test immediately after conditioning, and a second group performed the test 24 hours later. The stress or control procedure was administered immediately before the generalization test in both timing conditions.
Key findings
When participants were tested immediately after conditioning, the stress manipulation did not significantly change their fear responses or their ability to identify the shock-associated tone. By contrast, when the generalization test occurred 24 hours after conditioning, acute stress increased both subjective shock expectancy and physiological arousal, and it caused broader generalization across tones. Participants tested after a 24-hour delay without elevated cortisol showed only modest increases in fear and retained a clearer ability to discriminate the shock-associated tone.
These results indicate that acute stress promotes generalization of older threat memories but has little effect on recently formed memories. In other words, stress applied at the time of memory retrieval or reactivation after a delay makes older memories more likely to be broadly applied to new, safe stimuli.
Clinical implications
The study sheds light on mechanisms that may underlie the overgeneralization of fear seen in anxiety disorders and PTSD. Because stress can amplify the reach of older threat memories, periods of heightened stress may temporarily increase vulnerability to false alarms and exaggerated defensive responses. This insight could inform timing and approaches for therapies that target maladaptive fear memories, especially in populations exposed to repeated trauma.
Funding for the research was provided by the National Institutes of Health. Source reporting: Kimberly Berger, UT Austin.
Abstract
Stress promotes generalization of older but not recent threat memories
Acute stress can affect emotional regulation and may promote generalization of threat responses to harmless stimuli. Memory representations also change over time, becoming less precise and more gist-like, which can increase behavioral generalization. This study tested whether a single acute stressor administered either immediately after learning or following a delay would alter generalization of aversive learning. Healthy adults underwent auditory threat conditioning in which one tone was paired with an electrical shock and another tone was not. Generalization to novel tones was measured either the same day or 24 hours later, with stress induced immediately before testing. Anticipatory skin conductance responses and explicit shock expectancy ratings were recorded. Stress given shortly after conditioning did not affect generalization, whereas stress applied after a delay increased arousal and broadened generalization on both physiological and explicit measures. These findings show that acute stress increases generalization of older but not recent threat memories, with relevance for understanding overgeneralization in anxiety and stress-related disorders.