Interoceptive inputs are ascending information from the internal body. Cortical activities have been shown to be elicited by interoceptive inputs from the heartbeat at approximately 200–600 ms after the R wave, and sensory processing is modulated by the heartbeat within the time window. However, the influence of interoceptive inputs and their timing on corticospinal excitability has not yet been fully elucidated. Moreover, in previous studies, individual differences in interoceptive accuracy—objective accuracy in detecting internal bodily sensations assessed by heartbeat perception tasks—can be considered as an important factor influencing cortical activities by the heartbeat. We therefore investigated the modulation of corticospinal excitability by the heartbeat and its timing by recording motor-evoked potentials elicited by transcranial magnetic stimulation of the primary motor cortex at various timings from the R wave. We also investigated the relationship between this modulation and individual interoceptive accuracy. We found a significant positive correlation between the modulation of corticospinal excitability at 200 ms after the R wave and interoceptive accuracy. Conversely, we found a significant negative correlation between the modulation of corticospinal excitability at 400 ms after the R wave and interoceptive accuracy. These results indicated that the corticospinal excitability was modulated at 200–400 ms after the R wave (systolic phase) and that the timing of excitatory or inhibitory states in the corticospinal pathway differed with interoceptive accuracy. Although the neural mechanism remains unclear, these findings may aid in determining new factors influencing corticospinal excitability.

感知输入是来自体内的上升信息。研究表明，皮层活动是由R波后大约200-600 ms时来自心跳的感受性输入引起的，并且感觉处理在时间窗口内受到心跳的调节。然而，尚未完全阐明互感输入及其时机对皮质脊髓兴奋性的影响。此外，在先前的研究中，可以将个体间的感知准确度差异（检测通过心跳感知任务评估的内部身体感觉的客观准确性）视为影响心跳皮层活动的重要因素。因此，我们通过记录在R波的各个时间点经颅磁刺激初级运动皮层引起的运动诱发电位，研究了心跳对皮质脊髓兴奋性的调制及其时序。我们还研究了这种调制与个体感知精度之间的关系。我们发现R波后200毫秒皮质脊髓兴奋性的调制与感觉准确性之间存在显着的正相关。相反，我们发现在R波后400 ms皮质脊髓兴奋性的调制与感知准确性之间存在显着的负相关。这些结果表明，在R波（收缩期）后200–400 ms内，皮质脊髓兴奋性受到调节，皮质脊髓途径中兴奋或抑制状态的时机随感受性的准确性而变化。尽管神经机制尚不清楚，但这些发现可能有助于确定影响皮质脊髓兴奋性的新因素。