The effects of genes and trauma exposure on verbal memory among male twin Vietnam era veterans
Zink, Tyler A.
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Whereas a link between posttraumatic stress disorder (PTSD) and deficits in verbal memory has been well documented, evidence supporting the influence of trauma exposure without PTSD on verbal memory is more limited. The cunent set of studies examines the relationship between trauma exposure, PTSD, and verbal memory (encoding, retention, and recognition) among participants in the Vietnam Era Twin Study of Aging (VETSA) (N=1237 men; mean age=55.6). VETSA is a longitudinal study of genetic and environmental influences on the expression of cognitive, psychological, and health-related phenotypes. Participants include monozygotic and dizygotic twin pairs. Phenotypic and genetic analyses were conducted in order to determine whether trauma exposure and PTSD affect verbal memory in the same way. There were 478 men with trauma exposure, of whom 86 had PTSD, and 759 with no trauma or PTSD. Phenotypic analyses did not demonstrate a relationship between trauma and any aspect of verbal memory, but demonstrated associations between PTSD and recognition (though not encoding or retention). Monozygotic discordant twin analysis examined whether poor verbal memory reflected the effect of trauma (of any kind), PTSD, or genetic vulnerability to PTSD and revealed no significant effects. A fmal set of analyses examined whether trauma exposure or PTSD served as an environmental moderator of the heritability of encoding and recognition (retention was not significantly heritable). Environmental factors had a greater influence on the variance in encoding among subjects who had experienced trauma than among those who had not, and those who experienced trauma were significantly more variable in their recognition performance than were those who had not. In regard to PTSD specifically, the monozygotic discordant twin analysis and the environmental moderator analysis were considered exploratory, as the sample size provided limited power. Taken together, the results suggest that, despite an absence of main effects at the phenotypic level, trauma exposure significantly influences variance in aspects of verbal memory. These findings may alert clinicians to the importance of recommending that trauma-exposed individuals seek environmental opportunities to enhance verbal memory (i.e., tutoring or cognitive rehabilitation) and avoid environmental factors that may negatively affect it (i.e., substance use or sleep disruptions).
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