Individuals with posttraumatic stress disorder show a selective deficit in generalization of associative learning.

OBJECTIVE Drawing on two different populations, Israeli police and Hungarian civilians, the present study assessed the ability of individuals with posttraumatic stress disorder (PTSD) to generalize previous learning to novel situations. Past neuroimaging studies have demonstrated diminished medial temporal lobe (MTL) activation and/or reduced hippocampal volume in individuals with PTSD. Our earlier computational models of cortico-hippocampal function and subsequent experimental tests of these models in MTL-impaired clinical populations argue that even mild hippocampal dysfunction may result in subtle impairments in generalization. Therefore, we predicted that individuals with PTSD would show impaired generalization. METHOD We compared the performance of five groups from two countries, including 19 Israeli police with PTSD and 22 trauma-exposed police without PTSD, and 22 Hungarian civilians with PTSD, 25 trauma-exposed civilians without PTSD, and 25 individuals without PTSD unexposed to the same trauma. Participants were tested on a two-phase learning paradigm, the Acquired Equivalence Task, which measures the ability to generalize past learning to novel situations. RESULTS We found that both PTSD and non-PTSD participants were capable of learning the initial stimulus-outcome associations, F(4, 108) = 1.79, p = .14. However, as predicted, only individuals with PTSD showed a selective deficit in generalization of this learning to novel situations (F(4, 108) = 8.35, p < .001, Partial η2 = 0.26). CONCLUSIONS Individuals with PTSD show a selective impairment in generalization of past learning similar to other clinical populations with MTL/hippocampal dysfunction. This is consistent with an emerging view of PTSD as being not only an anxiety disorder but also a learning disorder.