Physiological and neural mechanisms of anxiety, negativity, and threat
Leah H. Somerville (Author), Dartmouth College Department of Psychological and Brain Sciences, Dartmouth College (Degree granting institution)
The objective of this thesis was to examine the neural and physiological substrates underlying the processing of aversive information, and how individual differences in anxiety influence these responses. In a series of experiments, we utilized skin conductance and functional neuroimaging (fMRI) methods to measure changes in autonomic arousal and neural activity in healthy adults varying in their level of dispositional anxiety. In one set of experiments, we measured transient and sustained neural and physiological activity while participants viewed negative and neutral pictures in temporally predictable or unpredictable contexts. In a second set, we utilized a shock threat paradigm to place people at varying levels of threat for 'earning' electric shocks that they would ostensibly receive later. Results indicated that physiological and amygdala responses were sensitive to transient negative cues, and the magnitude of responses was exaggerated in anxious individuals. In addition, high anxious individuals displayed sustained hypoactivity in the rostral anterior cingulate cortex, which predicted this exaggeration of amygdala response. Conversely, sustained activity in more lateral prefrontal regions, including the anterior insula and inferior frontal gyrus, tracked subjective nervousness related to temporally unpredictable states and proximity to shocks, and in the shock task, this response was exaggerated in anxious individuals. Taken together, these findings suggest that anxiety relates to hyperactive emotional responses in the amygdala, which may occur due to an underrecruitment of medial prefrontal control regions that modulate recovery from emotional responses. In addition, regions of the lateral prefrontal cortex may function to maintain tonic arousal states, with enhanced activation of these regions in anxious individuals. In summary, the processing style of dispositionally anxious individuals appears to be subserved by hyperactivation of limbic and lateral ventral prefrontal circuitry, in concert with a deficient recruitment in midline cortical control mechanisms. It is hoped that these findings shed light on the neural substrates underlying pathological anxiety disorders
Thesis, Dissertation, English, 2008