The influence of respiratory phases on interoceptive and exteroceptive perception

Abstract: Recent literature about interoception suggests that interoceptive accuracy and its related neural correlates (e.g., the heartbeat evoked potential) are enhanced during exhalation, while inhalation optimizes the processing of exteroceptive information. We herein investigated the relationship between respiratory activity and the perception of anticipated interoceptive and exteroceptive stimuli, which were signaled by a visual cue (i.e., a white cross turning red). We tested whether and to what extent the presence of a cue would prompt participants to actively modulate their breathing to enhance task performance. Forty-one participants engaged in both an interoceptive and an exteroceptive task, while their respiratory and cardiac activity were recorded. The interoceptive task was the Heartbeat Discrimination Task, where participants were instructed to judge the simultaneity of a sequence of three tones with their heartbeat. In the exteroceptive task, participants were asked to detect a near-threshold tactile stimulation over their left index finger. This paradigm allowed us to determine whether participants actively align inhalation and exhalation to the expected (i.e., cued) exteroceptive and interoceptive trial onset, respectively. By applying Signal Detection Theory, we assessed task performance and discrimination indices. We observed a significantly better performance during exhalation compared to inhalation in both tasks, indicating a modulation of perceptual processing by the respiratory cycle. Moreover, circular statistics revealed strong phaselocking of respiration to the expected (i.e., cued) stimuli onset during both the interoceptive and exteroceptive tasks. Generally, participants showed a tendency to align inhalation with trial onset. Additional analysis, including measures like inter-trial coherence, is required to better understand the role of respiration as an active sensing mechanism, optimizing the perceptual processing of both the interoceptive and exteroceptive domains, and its contribution to the understanding of how bodily rhythms shape and optimize human perception.