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Abstract
The affective salience network is composed of a variety of brain regions, including, but not limited to, the anterior insula, amygdala, and dorsal anterior cingulate cortex. Based primarily on fMRI studies, previous research suggests that activity in the affective salience network is related to suicidal behavior. The affective salience network’s specific role in suicidal behavior is not known, but one possibility is its core function in the orienting response to salient stimuli, including threat. This orienting response aids in survival and, if diminished to threatening stimuli, may underlie the affective salience network’s relationship to suicidal behavior by contributing to a key construct in leading theories of suicide: capability for suicide, specifically its subconstruct called fearlessness about death. Existing treatments for suicidal behavior are sub-optimal, and thus interventions targeting the affective salience network may prove beneficial in treating suicidal behavior by decreasing capability for suicide. In a first step towards investigating such an approach, Chapter 1 reviews the literature on capability for suicide, the affective salience network, neural measures of affective salience, transcranial magnetic stimulation (TMS) and how it can be used to stimulate subcortical areas. Chapter 2 discusses an attempt to use intermittent theta-burst stimulation (iTBS), a type of repetitive TMS, to alter affective salience network activity in healthy young adults by indirectly targeting a key region of this network: the amygdala. In line with previous research using a similar approach, a portion of the rostral medial frontal wall (RMW) that demonstrated high functional connectivity with the amygdala was stimulated to alter the affective salience network’s orienting response to affective pictures. To examine this neural activity, an event-related potential called the late positive potential (LPP) was measured. Analyses did not reveal any significant difference in the LPP between stimulating the RMW and a control site (V1). However, if effect sizes were to hold n a larger sample, the data suggest that iTBS stimulation to V1 reduces the affective salience network’s response to threatening images.
Chapter 3 discusses future directions based on the results presented in Chapter 2, and ends with remarks on the state of the suicide neuroscience field. Specifically, I discuss the assumptions in the present paradigm, and offer suggestions for how the field can improve.
In summary, this work failed to find a significant effect of stimulation to the RMW to alter the LPP. Nevertheless, the data suggests the possibility that V1 stimulation reduces the salience network’s response to threatening images. With further investigation, the relationship between V1 stimulation and salience network activity may inform the scientific community’s understanding of the relationship between sensory information and salience.
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