Movement-activated Auricular Vagus Nerve Stimulation in Rehabilitation

Transcutaneous auricular vagus nerve stimulation (taVNS) has emerged as a safe and medically approved non-invasive method for stimulating the vagus nerve, utilising a small electrode placed on the outer ear to transcutaneously activate an auricular branch of the vagus nerve. Studies indicate the potential benefits of both invasive and non-invasive vagus nerve stimulation for motor neurorehabilitation, particularly when combined with rehabilitation exercises. A recent pilot study has shown that pairing motor rehabilitation with taVNS in a movement-gated system resulted in improvement on Fugl-Meyer Assessment upper extremity scores and a greater effect size compared to an unpaired taVNS, while administering fewer stimulation pulses. This demonstrates that taVNS paired with movement therapy can reduce the intensity of stimulation, while still producing beneficial results. However, current approaches for performing stimulation during movement require either manual control or complex and non-specific sensor setup. There are no options for tracking and controlling stimulation based on movement kinematics in an objective, unsupervised manner. Therefore, an in-house developed taVNS system will be used (SmartVNS). The system includes inertial measurement unit (IMU) sensors to track patient's movement and then automatically initiates the taVNS stimulation during movements.

The benefit for participants in the study involving transcutaneous auricular vagus nerve stimulation (taVNS) paired with rehabilitation exercises outweighs the potential risks. The intervention, taVNS, is a medically approved procedure with minimal and extremely rare adverse effects, particularly when used within approved parameters. The study protocol ensures that taVNS will be administered at safe and tolerable intensity levels, with immediate removal of electrodes if any discomfort occurs. Additionally, the intervention will not alter the typical rehabilitation program of the participants, and motion-triggered taVNS will be while participants perform repetitive rehabilitation exercise movements with the affected limb. The potential benefits of the study include contributing to the quality of future neurorehabilitation outcomes and informing decisions for protocols in future clinical studies to explore the efficacy of taVNS in enhancing neurorehabilitation and motor learning in adults with motor deficits. Overall, the study aims to prioritise participant safety while offering the potential for meaningful therapeutic benefits.

Inclusion criteria

• Age ≥ 18 years
• Ability to follow study instructions
• At least 1-2 weeks after a stroke or traumatic brain/spinal cord injury and with a residual motor deficit.

Exclusion criteria

• Inability to give informed consent or understand the tasks, other neurological or psychiatric illness that could confound execution/recovery. E.g. Global inattention or receptive aphasia.
• Presence of ongoing dysphagia or aspiration difficulties
• Subject receiving medication that may significantly interfere with actions of taVNS on neurotransmitter systems at study enrollment
• Prior injury to vagus nerve, either bilateral or unilateral (e.g., injury during carotid endarterectomy)
• Severe depression (Beck Depression Scale > 29)
• Current use of any implanted electronic device, such as a pacemaker or other neurostimulator
• Medical or mental instability (diagnosis of personality disorder, psychosis, or substance abuse) that would prevent the subject from meeting protocol timeline
• Pregnancy or plans to become pregnant or to breastfeed during the study period
• Current requirement, or likely future requirement, of diathermy during the study duration