Mechanisms Underlying Emotional Memories

As an analogue to studying the mechanisms involved in posttraumatic stress reactions, this body of research investigated cognitive and biological factors underpinning the development of declarative and intrusive emotional memories, with particular emphasis on sex differences in emotional memory. Specifically, the studies investigated the role of sex hormones on proposed modulators of emotional memory via memory paradigms of negative and neutral stimuli in healthy student participants. Study 1 tested hypotheses concerning the impact of visual versus verbal encoding conditions on recall in males and females in two hormonally-distinct phases of the menstrual cycle. The findings revealed an advantage for mid-luteal women (high hormone) over late-follicular (low hormone) and males in mental imagery ability, which appeared to interact with progesterone in facilitating the encoding of visually-processed emotional stimuli. Study 2 examined the role of mental imagery during the consolidation of intrusive memories. Results showed that disruption of imagery via competition for visuospatial processing resources contributed to fewer intrusions in mid-luteal females but not follicular females. This study replicated results from Study 1 concerning menstrual phase-related differences in mental imagery ability and extended earlier findings to show that the interaction between progesterone and imagery is associated with more frequent spontaneous intrusions. Study 3 sought to test key tenets of a biological account of emotional memory, whereby males, mid-luteal females and follicular females viewed negative and neutral images whilst undergoing a functional Magnetic Resonance Imaging paradigm. Sex and stress hormones were assayed to investigate the hypothesised influences of neurobiological factors in modulating emotional memory. In line with earlier findings, mid-luteal females demonstrated greater mental imagery, and the progesterone by mental imagery interaction variable again predicted recall of emotional memories. Unexpectedly, the imaging findings suggested that males had greater activation in emotion processing centres of the brain during the encoding of emotional images compared to both groups of females, whilst mid-luteals showed heightened visual processing of arousing stimuli relative to follicular women. Together, the findings from this study suggest that sex differences in emotional memory may be partly underpinned by menstrual phase-related differences in the neural circuitry involved in sensory processing and the encoding of visual stimuli. Overall, the findings from this thesis shed light on prevailing cognitive and biological models of PTSD and suggest potential mechanisms underlying sex differences in the prevalence of memory-based disorders