Understanding Emotional Memory: Cognitive Factors

Abstract

The term Emotional Enhancement of Memory (EEM) describes the better memory of emotional compared to neutral events. When the EEM effect is measured after a delay the modulation model explains this effect very well, citing preferential consolidation of emotional events as the cause. However, the EEM effect can be observed before consolidation, an inexplicable result for the modulation model. Mediation theory offers an alternative explanation of the EEM effect: cognitive factors at encoding contribute to the immediate EEM (iEEM); namely attention, semantic relatedness, and distinctiveness processing (DP). The current research sought to further elucidate the neural underpinnings of DP - said to occur in 'mixed' lists of emotional and neutral stimuli - as a significant contributor to the iEEM. This was measured by comparing immediate free recall memory of emotional and neutral stimuli presented in mixed, and pure lists (emotional or neutral stimuli), using a specially formulated stimulus set which controlled for differential semantic relatedness (SeRENS, Chapter 3).Electroencephalography (EEG) and functional magnetic resonance imaging (fMRI) data provided preliminary evidence of neural encoding correlates of the iEEM (Chapter 4 and 5); data which is not predicted by the modulation model. The behavioural EEM effect found in mixed lists was driven by a reduction in neutral memory relative to pure lists; however neural correlates of this effect were minimal. Conversely, successful mixed list emotional encoding (relative to pure list emotional encoding and neutral encoding) correlated with greater neural activity associated with [bottom-up] attention (in P300 and right supramarginal gyrus) and semantic processing (late positive potential and left anterior superior temporal gyrus; EEG and fMRI evidence respectively); although this did not correlate with behavioural measures of memory. This behaviour-neuroimaging discrepancy can be reconciled when one considers the results of Chapter 6: the crucial iEEM behavioural effect of impaired neutral memory was associated with retroactive interference from proceeding emotional stimuli (especially when relational processing resources were depleted); a neural effect that cannot be captured by the current event-related designs. This suggests that what is captured in the neuroimaging data is the mechanism which drives the retroactive interference at the temporal locus of emotional stimulus onset.These results raise the possibility of two disociable EEM effects: the iEEM effect explained by poor neutral memory due to retroactive interference of proceeding emotional stimuli (mediation theory); and the delayed EEM effect explained by preferential emotional stimulus consolidation (modulation model). These explanations can be unified into one model; however further testing would be required to determine the endurance of cognitive contributions to the EEM effect.

Date of Award	1 Aug 2016
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Daniela Montaldi (Supervisor), Deborah Talmi (Supervisor) & Jason Taylor (Supervisor)