Multi-scale coupling of motor events to the cardio-respiratory cycle

An allostasis-first account proposes that the brain coordinates with the systems of the body to select actions based on predicted metabolic costs. However, it remains unclear how this coordination unfolds over different timescales of action (i.e., movements), and differs across body systems with different intrinsic timescales, such as breathing or the heartbeat. In the present study, we tested how eye and finger movements during a self-paced visual search task were coordinated in time with respiratory and cardiac cycles. We quantified coupling between each movement and physiological signal using a modulation index method, which quantifies non-uniformity in the distribution of movements across a physiological cycle. We performed several follow-up analyses to characterize when during a physiological cycle more or fewer movements occurred, and whether effects differed across participants. Aggregated across participants, our results demonstrated robust coupling between eye and finger movements and the respiratory cycle, as well as inhalation and exhalation phases. Coupling results were non-significant when examining the entire cardiac cycle, but follow-up analyses by systolic and diastolic phase indicated that eye movements were more or less likely at specific times within systole and diastole. Broadly, our results indicate that action is coordinated in time with cardiorespiratory cycles, in particular with the respiratory cycle, across a majority of our participant sample. These findings provide a foundation for future examination of how naturally occurring physiological cycles may coordinate with the timing of actions, and how metabolic resources may be efficiently managed through allostasis.