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Altered stimulus-response learning and striatal responses in posttraumatic stress disorder

Poster Session F - Tuesday, March 10, 2026, 8:00 – 10:00 am PDT, Fairview/Kitsilano Ballroom

Krystian B. Loetscher¹ (), DT Nguyen³, John H. Krystal¹, Stephanie M. Groman², Elizabeth V. Goldfarb¹; ¹Yale University, ²University of Chicago, ³University of Virginia

Posttraumatic stress disorder (PTSD) is a debilitating psychiatric illness related to alterations in learning and memory. Although PTSD studies largely investigate hippocampal and amygdala-dependent learning, evidence suggests that stress can enhance dorsolateral striatal-dependent stimulus-response (SR) learning. We hypothesize that individuals with PTSD would have enhanced and rigid SR learning. fMRI data was collected in participants (N = 35 PTSD, N = 35 trauma without PTSD) while they completed a probabilistic learning task. Participants were presented 6 unique stimuli where one of two actions was probabilistically reinforced for each. After learning (300 trials), the correct action reversed for some stimuli. Importantly, because stimuli were randomly interleaved, participants should not apply feedback over consecutive trials (trial-level), but rather over trials of the same stimulus (stimulus-level). Contrary to our expectations, the PTSD group was significantly slower to learn probabilistic associations. Participants in both groups were best fit by a computational reinforcement learning model with both stimulus and trial-level learning, although the PTSD group relied more on maladaptive trial-level learning. Consistent with our expectations, the PTSD group had greater difficulty updating learned responses, with significantly worse performance following reversal due to increased levels of perseveration. Supporting the role of the dorsolateral striatum, participants in only the PTSD group had larger putamen responses when learning to update behavior. These results suggest that while individuals with PTSD have difficulty learning probabilistic associations, when formed, they become rigid and difficult to update. This may be related to erroneously applying feedback, and greater reliance on striatal encoding strategies.

Topic Area: LONG-TERM MEMORY: Skill Learning