Dopaminergic involvement in positively and negatively valenced emotional memory in humans

Emotional events are generally remembered better than are neutral events, although experiments to date have predominantly explored the influence of negatively and not positively valenced emotions on memory. Previous studies have established that amygdala activity at least partially underlies the enhancement of memory for emotional materials. Although investigations in rodents have suggested a role for dopamine in this modulating process, very few experiments in humans have examined the influence of this neurotransmitter.;Experiments 1 and 2 of this dissertation were conducted to establish a paradigm for the study of the enhancing effects of positive emotion on recall, and findings suggest equivalent long-term recall for positive and negative emotionally arousing stimuli. Experiments 3 and 4 then explored the influence of dopaminergic activity on emotional memory. Experiment 3 utilized PET imaging with the D2/D3 receptor ligand 18F-fallypride, and results suggested a sex-specific lateralization of amygdala activity in relation to memory, as male subjects showed a tendency for better recall with decreased dopamine release in the right hemisphere amygdala, while female subjects showed a tendency for better recall with increased dopamine release in the left hemisphere amygdala. To clarify and extend these findings, Experiment 4 then used a pharmacological approach with the D2 agonist bromocriptine. Results suggested that bromocriptine administration caused a shift in the ratio of non-arousing to arousing pictures recalled, enhancing memory in favor of arousing stimuli of both positive and negative valences.;When considered together the studies presented here strongly indicate that positively valenced emotional materials can be as enhancing to memory as previously researched negative materials, and that dopaminergic activation modulates recall for both positively and negatively valenced information, biasing it toward emotional enhancement. Additionally, there are indications that on the neural level, amygdalar dopaminergic activity in response to emotional stimuli exhibits sex-specific lateralization, consistent with previous studies of emotional memory formation. The findings thus underscore the view that future studies of dopamine and amygdala function in emotional memory should control for the influences of subject sex.