The goal of this research was to develop a functional magnetic resonance imaging paradigm for use in investigating major depressive disorder. Functional neuroimaging studies of depression have reported altered resting brain metabolism and altered responses to simple emotion paradigms in the amygdala, ventral prefrontal cortex, and anterior cingulate cortex. We studied healthy individuals? responses to complex emotion paradigms to attempt to distinguish activity in these regions. We hypothesized that the amygdala mediates ?bottom-up? processing driven by emotional stimulus content, and that the ventral prefrontal cortex and anterior cingulate cortex mediate ?top-down? processing driven by explicit knowledge or intention. In the first experiment, we tested whether matching faces by emotional expression elicited a bottom-up response in the amygdala. The amygdala responded during matching of both emotional and non-emotional faces, implying that this response was driven by top-down demands of the task. In the second experiment, we measured responses during rating of emotional pictures. The response in the amygdala was greater to unpleasant than pleasant pictures, regardless of rating task: a bottom-up response. The response in the ventral prefrontal cortex was greater to emotion rating than non-emotional rating, regardless of picture content: a top-down response. The anterior cingulate cortex showed weak, mixed bottom-up and top-down responses. This emotion rating paradigm improves existing approaches to imaging the neural bases of major depressive disorder by eliciting dissociated responses in two regions implicated in depression: the amygdala and orbitofrontal cortex. This paradigm may be used in future studies to investigate in parallel the effects of depression on bottom-up and top-down emotion processing. Future studies may attempt to elicit more specific responses in the anterior cingulate cortex by using paradigms in which emotional stimuli interfere with the performance of cognitive tasks.
|Date of Award
|Yijun Liu (Supervisor), Christiana Leonard (Supervisor), Dawn Bowers (Supervisor) & Russel Bauer (Supervisor)