Memory impairment in patients with posttraumatic stress disorder

Abstract

This study was initiated to examine verbal learning and memory impairment in patients with posttraumatic stress disorder (PTSD). A growing number of studies have found verbal learning and memory impairment in war veterans with PTSD. However, research on these matters in refugees is sparse. The contribution of PTSD versus concurrent symptoms of depression on memory functions needs further investigation. In addition, the strength of memory impairment across studies is not known, and the effect of factors such as trauma type, comparison groups used, and memory measures are lacking.

In Paper I and II the focus was on verbal learning and memory alterations in refugees exposed to actions of war and political violence. Twenty-one refugees exposed to war and political violence with chronic PTSD were compared to an exposed control sample of 21 refugees without PTSD. No differences were found in attention span, but tests of verbal memory showed less efficient learning in the PTSD group. Group differences in delayed recall could be explained by learning efficiency. No differences were seen in recognition memory. These results indicated that memory alterations in PTSD are related to impaired acquisition and less effective encoding of the memory material and not to impaired attention span or impaired retrieval. Self-reported depressive reactions and self-reported intrusive reactions were the most important factors for explaining the variance in memory impairment in PTSD.

In Paper II, mechanisms underlying the memory impairment were investigated further. Verbal learning and memory are dependent on the individuals’ ability to organize verbal information appropriately during acquisition. Differences in the use of organizational strategies when processing memory material in the PTSD group and the control group were tested. The results demonstrated that the PTSD group compared to the control group used less serial clustering as an organization strategy during learning. This may explain way the PTSD group demonstrated impaired verbal learning and memory. The semantic organization of the memory material was slightly reduced in both groups. Analyzing for serial-position effects the PTSD group reported more items from the recency region of the list. This could indicate a tendency to use a passive recall strategy of echoing back the last items presented. In addition, intrusive errors were significantly increased in the PTSD group. The data support an assumption of changes in memory strategies in patients with PTSD and a specific impairment to perform executive control. The study further showed that the use of ineffective organization strategies was not only related to PTSD symptomatology, but also to selfreported symptoms of depression and general distress.

Several reviews of the research in this field have indicated that impairment in verbal learning and memory are the most consistent cognitive impairments observed in patients with PTSD. The results from our first study supported these findings. However, the verbal learning and memory studies have yielded inconsistent results. Most of the studies including ours have been conducted on small sample sizes in efforts to use stringent diagnostic criteria and to equate the patient groups and control groups on key variables. The studies therefore suffer from insufficient statistical power. To investigate the strengths of the short-term memory impairment across studies a meta-analysis was performed in Paper III. Twenty-eight empirical research studies published from 1993 to April, 2007 met our inclusion criteria. Overall, the present findings suggest that patients with PTSD have significant impairment in verbal memory measured with free recall tests compared to controls, as evident by the moderate effect sizes. Marked impairment was found in verbal memory performance in patients with PTSD compared to healthy controls, and more modest reductions were found in performance in patients relative to exposed non-PTSD controls. Furthermore, the findings suggest that memory impairment is related to trauma type. Stronger effects were found in war veterans than for individuals exposed to sexual- and physical abuse. Rather unexpectedly no effect was found for the sexually abused PTSD groups compared to exposed controls. This may be related to the fact that exposed control groups have sub-clinical symptoms that affect the relationship.

The present studies support the assumption of verbal memory impairments following PTSD in refugees and other groups exposed to traumatic events. This verbal memory impairment may have psychosocial consequences and implications for treatment. These results suggest that clinicians should apply screening instruments and avoid cognitive demanding treatment methods. Future research should examine the functional consequences for the patients. Furthermore, future research should also focus on examining the hypothesis that some degree of memory dysfunction may be present in individuals at risk for PTSD.