Does Remembering Cause Forgetting in Chronically Stressed People? : A Study of Ugandan Civil War Refugees With and Without PTSD

Abstract

People suffering from posttraumatic stress disorder (PTSD) often have reduced episodic memory performance as well as intrusions and flashbacks of traumatic events. Hippocampal and prefrontal dysfunctions are assumed to be responsible. Using a modified retrieval-induced forgetting paradigm, we investigated episodic memory performance in a group of German participants and in civil war victims with and without PTSD in Northern Uganda. Retrieval-induced forgetting is an adaptive mechanism in memory and refers to the fact that retrieval of target elements impairs subsequent recall of related material. Retrieval-induced forgetting depends on medio-temporal and prefrontal functions and acute stress eliminates the effect. Here, using a pictorial retrieval-induced forgetting paradigm, retrieval-induced forgetting was found in a German group, but not in Ugandan refugees, neither in those with nor without PTSD. As both groups were exposed to multiple, often severely traumatic events, stress exposure in both Ugandan groups may account for this finding. Specific to Ugandan refugees with PTSD, an elevated false alarm rate during recognition testing was found, although even refugees without PTSD had higher false alarm rates than the German group. In the civil war victims, stress-induced memory dysfunction may impair hippocampus-mediated contextual binding, eliminating retrieval-induced forgetting and reducing the ability to differentiate between old and new pictures. Traumatic stress may additionally disrupt prefrontal inhibition mechanisms, leading to an inability to suppress false alarms.