A specific deficit in spatial memory acquisition in post-traumatic stress disorder and the role of sleep in its consolidation

Posttraumatic stress disorder (PTSD) is characterized by the presence of anatomo-functional hippocampal alterations. To date, the ability to orient within the environment, which relies on hippocampal integrity, has never been investigated in PTSD. We hypothesized that the ability to form a cognitive map of the environment would be impaired in PTSD. Moreover, spatial memory consolidation benefits from postlearning sleep. Because PTSD individuals often complain about sleep disturbances, we hypothesized that any sleep effect on memory performance would be hampered in these subjects. Twenty-two subjects, all survivors of the L'Aquila 2009 earthquake, were divided into a PTSD and a control group, based on clinical evaluation. After an acquisition phase, they were tested twice ("test" and "retest") on a virtual navigation task. In addition, participants were administered the Digit Span and Task Switching. Subjective sleep quality and sleep disturbances were also assessed. The two testing sessions were on consecutive mornings, interspersed with a night of sleep. During the acquisition phase, the PTSD group took more than twice as long to form a cognitive map of the environment compared to the control group. However, once this phase was successfully completed, the two groups did not differ at test, but they tendentially differed at postsleep retest. Additional analyses comparing performances between groups on test-retest difference scores confirm that sleep-dependent consolidation may be differentially affected in the two groups. Our findings are strictly confined to the navigation performance, excluding a generalized cognitive deficit. PTSD also reported more subjective sleep disturbances and shorter sleep time than controls, which were correlated to worse performance at retest. The specific deficit in the formation of a cognitive map reported in PTSD may be related to hippocampal dysfunctions as well as to the sleep disturbances experienced by these patients. The possible deficiency of sleep-dependent spatial performance improvement should however be confirmed by further studies comprising a wake control group