Slower Respiration Rate Predicts Lower Pain Sensitivity and Greater Supramarginal Gyrus Activation

Abstract

The subjective experience of pain is driven by multiple physiological and psychological mechanisms supported by a dynamic interplay between low-level afferent input and higher-order cerebral mechanisms. Volitional changes in respiration rate predict changes in pain. However, it is unknown if naturally slower breathing rate is associated with lower pain sensitivity. Further, the brain mechanisms supporting breathing rate during noxious and innocuous stimulation have not been identified. Seventy-four healthy volunteers were administered innocuous (35°C) and noxious heat (Medoc; ten, 12s plateaus of 49°C) to the back of the right calf during pseudocontinuos arterial spin labeling fMRI acquisition (TI = 3 s, TE = 12 ms, TR = 4 s, reps = 66). A visual analogue scale (0 = no pain – 10 = worst pain imaginable) was used to collect pain intensity ratings after each fMRI series. Respiration rate was continuously acquired using a respiratory transducer (Biopac Systems). Linear regression analyses tested the hypothesized relationship between respiration rate and pain sensitivity (SPSS). Standard preprocessing of the functional images included 9 mm spatial smoothing, registration to MNI template and white matter signal regression. A whole-brain analysis examined the between-subjects neural correlates of respiration rate during noxious heat scans (FSL, z>3.1, cluster corrected p<0.05). Slower respiration rate during noxious and innocuous heat predicted lower pain intensity ratings (r = .26, p = 0.03; r = .28, p = .02 respectively). Slower breathing rate was associated with higher cerebral blood flow in the right supramarginal gyrus (SMG) during noxious heat. Individuals that naturally breathed slower during noxious and innocuous stimulation reported lower pain sensitivity. This is supported by stronger activity in the ipsilateral SMG, a region associated with higher somatic-awareness and attention-reorienting towards endogenously-driven stimuli. We propose that individuals that naturally breath slower might engage pain modulatory mechanisms through higher self-awareness.