Cardiac activity impacts spinal cord excitability. A Call to Return to the Roots
The heart continuously shapes neural processing and behavior through cardiac-brain interactions. While cortical excitability fluctuations and their role in cardiac-dependent cognitive and sensorimotor phenomena have been extensively studied, the temporal dynamics and contribution of spinal excitability oscillations across the cardiac cycle remain poorly characterized. In this study, we examine whether motor evoked potentials elicited by magnetic stimulation of the spinal cord are modulated by the cardiac cycle phase in healthy participants. Real-time adapting ECG-triggered stimulation enabled precise targeting of five phases across the cardiac cycle. Spinal excitability was significantly phase-dependent, with MEPs peaking during late diastole. MEPs amplitude was also found to be modulated by preceding cardiac intervals, where shorter intervals predict stronger diastolic facilitation. These findings establish that spinal excitability is rhythmically modulated by the cardiac cycle, potentially through blood pressure-mediated mechanisms. Notably, the diastolic facilitation observed here contrasts with previously reported motor cortex excitability profiles, indicating a non-synchronous cardiac modulation of spinal versus cortical excitability. These results may benefit neuromodulation approaches for motor and psychiatric disorder treatment and emphasize the critical importance of including spinal measures in future heart-brain interaction studies.