Research reportConsistent impaired verbal memory in PTSD: A meta-analysis
Introduction
The present study is a meta-analytic study that estimates the relationship between posttraumatic stress disorder (PTSD) and verbal memory impairments. Problems with concentration and memory in everyday situations are often reported by PTSD patients in clinical settings. Difficulties with concentration, intrusive recollections of the traumatic event, and yet inability to recall important aspects of the trauma are all different types of memory disturbances integrated in the diagnostic criteria for PTSD (DSM-IV-R; American Psychiatric Association, 2000). The symptoms connected to problems with everyday memory are however not included as a criteria.
Neuropsychological studies have documented that PTSD is associated with significant impairment in cognitive functioning (e.g. *Yehuda et al., 1995, *Vasterling et al., 1998, *Gilbertson et al., 2001). Studies have found that cognitive impairment in patients with PTSD specifically represent problems with attention and verbal memory functions (*Vasterling et al., 1998, *Yehuda et al., 2004). More recently, several studies have documented a more specific impairment in the memory process related to acquisition and encoding (*Yehuda et al., 2004, *Yehuda et al., 2005, *Johnsen et al., 2008). Several reviews of the literature have in addition suggested that the memory impairment in PTSD is modality specific, with a stronger pronounced impairment in verbal than in visual stimuli (Horner and Hamner, 2002, Vasterling and Brailey, 2005). Although fairly consistently reported, verbal memory alterations in PTSD do not seem to be found in all studies (e.g. *Crowell et al., 2002, *Neylan et al., 2004).
The literature suggests a number of factors that may affect the memory performance of patients with PTSD, both clinical factors and study characteristics. Such factors may be type of trauma, comorbidity, control groups used and memory test used. War veterans and women exposed to sexual and physical abuse in childhood or as adults, have frequently been selected for studying the relationship between these factors (Knight and Taft, 2004). In addition, mixed traumas have been included in some studies where both physical assault and motor accidents and the like are examined together. Stein et al. (2002) have emphasized that differences in the characteristics of cognitive dysfunctions across traumas are to be expected. In studying the memory impairment in patients with PTSD, both comparisons with healthy control groups or exposed non-PTSD groups have been common approaches. Some studies have included both types of control groups, but this kind of design has been less frequent. Yehuda (2005) has argued that the exposed non-PTSD controls groups are a challenging group to include because they may have variable sub-clinical symptomatology, but these control groups are important comparisons in understanding how exposed individuals with and without PTSD differ on cognitive variables.
Although some qualitative review papers have reported specific impairment in initial acquisition and memory (e.g. Buckley et al., 2000, Horner and Hamner, 2002, Isaac et al., 2006), a profile of memory impairment has been difficult to reveal. These review papers have used qualitative methods to describe the effects, and consequently they have not been able to estimate the strength of the memory-PTSD association or examined the differential strength of association within different trauma groups. An additional problem is that the research within this area has been conducted on small sample sizes in an effort to use both stringent diagnostic criteria and to equate the patient groups and control groups on key variables. Each study, therefore, has low statistical power. It has been suggested that the most suitable way to examine associations between constructs, such as memory and PTSD, is to rely on effect size values examined within meta-analyses (Lipsey and Wilson, 2001). In a meta-analytical approach, the relationship between PTSD and memory impairment may be established more clearly, because the analysis synthesize effect sizes across a representative collection of studies and provides greater power to detect group differences.
During the present research, Brewin et al. (2007) published a meta-analytical study on memory impairment in PTSD. This study established a moderate association between verbal memory and PTSD, but the effect of memory measures and control groups within different trauma was not examined.
The first aim of the present review is to meta-analyze the verbal memory findings of existing studies in order to determine the extent of verbal memory impairments in patients with PTSD. The second aim is to test differences in effect within specific types of traumas. The third aim is to test if the effect is dependent on the control group the patient group is compared with, either a healthy control group or an exposed control group without PTSD. Finally, we examine if the effect is dependent on the memory measures used.
Section snippets
Literature search
Published studies, that examined the relationship between verbal memory functioning and PTSD, were gathered through the use of the databases PubMed, PsychINFO and ISI Web of Science from 1989 to April 2007. The keywords used were “cognitive”, “memory”, “neuropsychological”; each of them in combination with “posttraumatic stress disorder” or “PTSD”. In addition, reference lists from these articles and journals, frequently publishing in the target domain, were searched. No attempt to locate
Overall effect of verbal memory impairment
Table 2 presents the results of the meta-analysis on the difference in verbal memory measures between PTSD groups and both control groups. In addition, the table presents the results separately for the comparison of the PTSD groups and the groups of healthy controls and exposed non-PTSD controls. Verbal memory is significantly impaired in PTSD. All analyses yielded highly significant z values for the difference in memory between patients with PTSD and comparison subjects. The magnitude of the
Discussion
The purpose of this meta-analysis was to assess to what extent PTSD is related to verbal memory impairment and whether the relation is influenced by trauma type, control participants, and memory tests used. Overall, the present findings suggest that patients with PTSD have significant impairments in verbal memory measured with free recall tests compared to controls, as evident by the moderate effect size (d = 0.74). Specifically, more marked impairments were found in verbal memory performance
Conclusions
In summary, this meta-analysis confirms that verbal memory impairment is present in adults with PTSD, and they are consistent across studies. Stronger effects were seen for war veterans compared to individuals exposed to sexual- and physical abuse. Marked impairment was found for verbal memory performance in patients with PTSD compared to healthy controls, while modest impairment was found in performance in patients relative to exposed non-PTSD controls. However, our study was restricted to one
Role of funding source
This study was funded by the University of Bergen.
Conflict of Interest
Both Grethe E. Johnsen and Arve E. Asbjørnsen declare that they have no conflicts of interest.
Acknowledgement
This study was financially supported by the University of Bergen.
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References marked with * indicate studies included in the meta-analyses.