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• Previous research revealed that the breathing system is involved in diverse motor processes including running, orofacial movements, and even voluntary motor action. • In this study, we investigated whether the breathing system is associated with voluntary initiation of mental actions (i.e., motor and visual imagery) which are not accompanied by any overt movement. • We found that the breathing cycle is synchronized with the onset of self-initiated mental imagery performance which was preceded by the cortical readiness potential. • Our findings suggest breathing-action coupling is involved in more general action preparation processing, regardless of any subsequent motor process. Previous research has suggested that bodily signals from internal organs are associated with diverse cortical and subcortical processes involved in sensory-motor functions, beyond homeostatic reflexes. For instance, a recent study demonstrated that the preparation and execution of voluntary actions, as well as its underlying neural activity, are coupled with the breathing cycle. In the current study, we investigated whether such breathing-action coupling is limited to voluntary motor action or whether it is also present for mental actions not involving any overt bodily movement. To answer this question, we recorded electroencephalography (EEG), electromyography (EMG), and respiratory signals while participants were conducting a voluntary action paradigm including self-initiated motor execution (ME), motor imagery (MI), and visual imagery (VI) tasks. We observed that the voluntary initiation of ME, MI, and VI are similarly coupled with the respiration phase. In addition, EEG analysis revealed the existence of readiness potential (RP) waveforms in all three tasks (i.e., ME, MI, VI), as well as a coupling between the RP amplitude and the respiratory phase. Our findings show that the voluntary initiation of both imagined and overt action is coupled with respiration, and further suggest that the breathing system is involved in preparatory processes of voluntary action by contributing to the temporal decision of when to initiate the action plan, regardless of whether this culminates in overt movements. [ABSTRACT FROM AUTHOR]