Change in a person's cognitive/emotional state, including expecting pain, is linked to connectivity change in identified brainstem and spinal cord networks

Resting-state functional MRI examines activity of the central nervous system in the absence of a specific task or stimulus, and has been used to investigate coordinated activity within the cerebral hemispheres, as well as the brainstem and spinal cord. While previous research has shown coordinated resting-state BOLD fluctuations in the brainstem and cord, the extent of resting-state networks (RSNs) and their function are still unclear. Characterizing these networks is an important step towards understanding the complex processing that occurs in the spinal cord and brainstem outside of a reaction to a stimulus. The overall aim of this thesis was to investigate the function of spinal cord and brainstem RSNs, by examining how these networks change when participants are experiencing different cognitive states. If a person’s cognitive/emotional state can be shown to influence resting-state BOLD signal fluctuations in the brainstem/cord, then we can infer that a function of these RSNs is to modulate the excitability of spinal cord neurons. We first aimed to confirm the presence of RSNs in the brainstem and spinal cord. After doing so, we present evidence that, while RSNs are largely consistent across 3 conditions (a resting-state condition, an audio presentation, and a video), watching a video or listening to an audio presentation alters these networks in specific ways. Combined with prior evidence, these results show that the observed networks likely help integrate homeostatic autonomic functions. Building on this evidence, we investigated how connectivity in the previously-identified networks is altered when a participant is specifically expecting pain. We provide evidence that coordinated brainstem and spinal cord networks are affected by the expectation of pain differently than by other distracting situations such as focusing on a video. We conclude that these networks may serve to integrate autonomic regulatory functions with pain processing. Linking the function of these networks to homeostatic autonomic control and pain modulation is an important step in understanding the complex brainstem/spinal cord activity that occurs aside from a reaction to a painful stimulus. Findings of this thesis will help provide a deeper understanding of pain modulation and subjective experiences of pain, such as placebo/nocebo effects.