Severe PTSD symptoms magnify episodic memory-encoding deficits and amygdala–ACC attenuation during unpredictable threat

PTSD is marked by atypical coupling between emotion and learning, yet it remains unclear how threat that is situational (the presence of potential danger) shapes episodic memory. We investigated whether unpredictability-driven threat alters incidental memory formation as a function of PTSD symptom severity (PTSDss). Sixty male combat veterans underwent fMRI scanning during incidental encoding of everyday objects presented under unpredictable threat (U), predictable threat (P), or no threat (N). Threat was operationalized as potential exposure to a highly aversive sound. An unexpected recognition test followed 90 minutes later. We related memory (hit rates), subjective anxiety, and encoding-related BOLD activity to PTSDss assessed with CAPS-5. Greater PTSDss predicted heightened anxiety and poorer memory for items specifically presented under unpredictable threat. While amygdala and dorsal anterior cingulate activity during encoding tracked overall memory success, these responses were attenuated with increasing PTSDss in the U condition. By linking unpredictable threat to both behavioral and neural markers of disrupted episodic memory encoding, the study helps explain how memory-related symptoms may develop and persist in PTSD.