Several new developments in neuroimaging techniques have paved the way for advances in understanding cortical-brainstem-autonomic and cortical-hypothalamic-endocrine pathways. Advances come from both acquisition techniques, including the development of spin-echo continuous arterial spin labeling (SE-CASL) fMRI, and improvements in analysis tools, including the development of multi-level path models capable of localizing and making population inference on brain pathways. In this project, the novel combination of these two techniques will be used to accomplish two aims: First, to identify cortical-brainstem and cortical- hypothalamic pathways mediating peripheral responses to social evaluative threat (Aim 1), and second, to examine modulation of functional threat-pathway strength by the prefrontal cortex (Aim 2). The ability to identify brain pathways involved in threat is important because a large literature in animals and humans suggests that psychological threat and `stress'are potentially linked to adverse outcomes in many diseases, including cardiovascular health, asthma, wound healing and immune function, depression, and others. But there is a critical gap in knowledge about the specific brain mechanisms that link psychological threat to peripheral activity in humans. Questions about brain mechanisms of emotion and questions about endocrine and autonomic physiology have largely been addressed by separate studies in separate fields. Using path analysis to examine both CASL-fMRI and peripheral responses (cortisol and basic measures of autonomic output) will allow us to forge links between `higher cortical'brain activity, subcortical centers in hypothalamus and brainstem, and peripheral responses. Identifying brain pathways is a new endeavor, as most fMRI studies examine regional brain activation, either ignoring how brain regions are connected or analyzing simple measures of connectivity between two regions. Path analysis can be used to identify pathways that span multiple regions and measures, providing potential for new insights into human brain-peripheral communication. SE-CASL was selected as a technique because it is particularly suited to studying the hypothalamus and brainstem, with improved spatial localization, more reliable signal and reduced artifacts around these regions, and stability over time, making it suitable for examining sustained brain and physiological responses to social evaluative threat.
Threats to both physical safety and social status produce marked autonomic and neuroendocrine responses in humans, and chronic physiological threat responses are associated with a number of disorders, including depression, anxiety, cardiovascular disease, infection, and others. Though threat responses have been carefully studied in nonhuman animals, little is known about the specific cortical-brainstem-body pathways that translate uniquely human cognitions about the social situation into physiological responses. This project combines advanced multivariate analysis techniques with cutting-edge methods for imaging the brainstem to map these pathways, providing insight into how threat responses are generated and regulated in the human brain.
