Lack of sleep-dependent spatial memory consolidation in post-traumatic stress disorder survivors of 2009 L’Aquila earthquake.

Objectives: Neuroimaging studies have revealed reduced volume and abnormal functional response of the hippocampi in patients with posttraumatic stress disorder (PTSD). In healthy subjects, recent neuroimaging findings showed that the hippocampus is critically involved in the formation and use of a mental representation of the environment, namely a cognitive map, and that its structural integrity affects the individual’s ability to orient within the environment. Recently, we have documented that spatial performance improvement in healthy subjects occurs only when spatial learning is followed by a period of sleep. Here, we investigated whether the ability to create a cognitive map is preserved in PTSD, and whether PTSD patients exhibit a sleep effect on spatial learning as documented in healthy subjects. Methods: The study included 10 PTSD subjects, survivors of the L’Aquila earthquake on 6 April 2009 (9 women, mean age: 21.7 ± 2.8 years) and 10 healthy controls (CON, 7 women, mean age: 24.2 ± 4.2 years). PTSD was diagnosed according to DSM-IV-R and all patients underwent a clinical and neuropsychological evaluation (Davidson Trauma Scale; Civilian Mississippi Scale; Emotion Attribution Task; Empathy Quotient). Participants performed a computerized 3-D virtual navigation task in which they were required to form a cognitive map of the environment (L, learning phase), followed by a retrieval task in which they were tested on the use of the cognitive map, which was tested before (test, T) and after (retest, R) one night of sleep. The time (sec) spent to form and make use of the cognitive map during test and retest was treated as dependent variable and submitted to a mixed design ANOVA with Group (PTSD, CON) as between factor and Session (L, T, R) as a repeated measure. Results: The ANOVA showed a significant Group x Session interaction effect. Post-hoc comparisons showed that controls subjects formed the cognitive map faster than PTSD. In addition, control subjects showed a significant sleep-dependent performance improvement, an effect that was not significant in the PTSD group. Conclusion: These findings indicate that PTSD is associated with an impaired ability to form a cognitive map of the environment, and that the well-known sleep-dependent spatial performance improvement could be not warranted in patients with PTSD. Both effects may be related to structural or functional hippocampal abnormalities.