Characterization of psychophysiological responses to pressure pain

Pain stands at the intersection of multiple health crises and is a leading contributor to disability. Current pain assessments rely on self-reports (which assume a capacity to understand and verbalize mental and emotional states) and behavioral observation which can be subject to limitations and misinterpretation. Subjective methods to evaluate pain can be substantially enhanced with objective biometrics that incorporate the sensory, motor, and psychophysiological aspects of the full pain experience. This thesis questions how experimentally induced pressure pain influences motor and cardiac activity (biophysical signals) elicited via the peripheral somatic and autonomic nervous systems, respectively. This work uncovers signatures in the biophysical responses to pain as subjects perform motor-cognitive tasks such as resting, drawing, and pointing to a target, under control and pain conditions. During the pain condition, sustained pressure is induced on the nonperforming arm via a standardized pain induction procedure that mimics pathological pain. Each of the tasks used in this study require different levels of cognitive effort and motor skill, helping reveal unique aspects of how the nervous systems respond to pain. Motion sensors are used to record the kinematics of various limbs of the body while electrocardiographic sensors are utilized to measure the electrical activity of the heart. These biophysical responses are also assessed in consideration of subjective pain ratings. This multi-method design allows us to evaluate the relationships among physiological, motor, and cognitive processes associated with pain via a unified statistical framework, along with traditional measures such as heart rate variability (HRV). The biophysical responses of the nervous systems are assessed via personalized analysis of the moment-by-moment fluctuations in the time series signals. These include variations in the amplitude of the body’s kinematics and in the timings of the heart’s inter-beat-interval. Movements elicited during experimental tasks have varying levels of spontaneity (which occur largely beneath awareness), and deliberateness (goal- directedness) that is under conscious control. These kinesthetic processes are susceptible to environmental and bodily changes and thus can help reveal how pain influences the body’s proprioceptive system. Autonomic responses such as cardiac activity serve as inevitable processes which cannot be volitionally controlled. They exhibit a narrower range of dynamics, helping provide robust signatures of the body’s responses to pain. We find that the pain’s influence on the body’s motor system depends on the motor and cognitive demands of the experimental task at hand. Pressure pain also elicits shifts in the stochastic signatures and HRV of the cardiac signal, regardless of the sensory-motor and cognitive demands of the task. Unique relationships are also observed between the objective metrics obtained from the biophysical data and self-reported pain ratings. Such methods are novel to the study of pain as they evaluate, in tandem, the continuous physiological signals harnessed from the peripheral (somatic and autonomic) nervous systems. The implications of this work are discussed in the context of precision medicine with possible applications in clinical populations.M.S.Includes bibliographical reference