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. We investigated the SoA, SoO, and brain activity in situations where participants moved their wrists voluntarily, or where EMS was applied either during voluntary movement or at rest. 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 were maintained at levels comparable to those during voluntary movement alone when EMS was applied during voluntary movement at intensities ranging from the motor threshold to a moderate level. Brain activity during passive movements induced by EMS was low, and activity during voluntary movements with EMS at various intensities was comparable to that during voluntary movements without EMS. Our results indicate that applying EMS at intensities from the motor threshold to moderate levels during voluntary movement is appropriate for maintaining SoA and SoO.