Moderate electrical muscle stimulation during voluntary movement does not disrupt the sense of agency or ownership

Although electrical muscle stimulation (EMS) is expected to alter the sense of agency (SoA) and sense of ownership (SoO) of a user's body parts, as well as brain activity during passive movements, these phenomena have not yet been systematically examined. Therefore, we investigated the SoA, SoO, and brain activity in situations where participants moved their wrists voluntarily, or where EMS was presented either during voluntary movement or at rest. Eighteen healthy individuals (16 males and two females; age: 18-29 years) participated in this study. The EMS intensity was varied from the motor threshold to the maximum level at which participants did not experience pain or discomfort. SoA and SoO scores were comparable to those during voluntary movement alone and when EMS was presented during voluntary movement at medium or low intensities. The change of electroencephalography power in the alpha (8-12 Hz) and beta (13-30 Hz) bands could not reveal the effect of EMS. Based on our findings, EMS at medium or low levels appears to be favorable for maintaining SoA and SoO.