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Abstract

Introduction: Recent accounts suggest respiration is used to actively adapt neural excitability to contextual demands to thereby improve sensory information sampling. A cardinal role has been attributed to the rhythmic stimulation of olfactory structures - by anatomy specific and phase locked to nasal breathing. The entrainment of faster neural oscillations is thought to propagate from thereon. With this behavioural pilot we investigate the impact of nasal (vs. oral) respiration on somatosensory perception. Secondly, we aim to assess cardiorespiratory effects on perceptual sensitivity given the intertwinement of both bodily functions and previous findings of cardiac phase shifts in sensitivity favouring diastole.
Methods: Twenty-one non-clinical adults participated in a somatosensory yes/no detection task under nose and mouth breathing (4 consecutive blocks per condition, order counterbalanced). Always under nose breathing and prior to each block, a near-threshold assessment was done to select in-block intensities. In each trial, participants indicated whether they felt a weak electrical stimulus delivered to their left index finger. Throughout the experiment, cardiac and respiratory signals were recorded (respiration belt, ECG, pulse oximetry). Nose clips and mouth tapes were used for experimental control of breathing.
Results: Hit rates were lower than priorly estimated which necessitated exclusion of six participants. A within-person comparison of perceptual sensitivity between both breathing routes yielded a small effect in favour for nasal respiration. There was no evidence for a shift in response criterion. Across the respiratory cycle and in both conditions, mean hit rate and perceptual sensitivity were significantly decreased during a phase attributable to early inspiration. However, participants reported having breathed less freely in mouth than nose blocks.
Discussion: We propose changes to the design regarding block length and order, the use of an adaptive staircase procedure within blocks, and a refinement of breathing control. Given their incorporation, we suggest repeating the experiment in a bigger sample incorporating EEG.