Application of Transcutaneous Auricular Vagal Nerve Stimulation in Motor Rehabilitation after Stroke

Transcutaneous auricular vagus nerve stimulation (taVNS) activates neural pathways akin to those of invasive vagus nerve stimulation (iVNS), boasting advantages such as non-invasiveness, low cost, safety, and high tolerability, indicating promising prospects as an alternative neuromodulatory technique for motor function rehabilitation post-stroke. However, there is a lack of consensus on specific application parameters and therapeutic effects of taVNS, with the underlying mechanisms remaining to be elucidated. This review comprehensively examines the application of taVNS in post-stroke motor rehabilitation, encompassing its use in non-synchronous and synchronous upper limb training, as well as monotherapy, alongside its mechanisms of action, which include anti-inflammatory and neuroprotective effects, enhancement of blood-brain barrier integrity, and modulation of cortical excitability and neuroplasticity, along with an analysis of stimulation parameters, safety, and efficacy. However, the current landscape is characterized by a scarcity of high-quality clinical studies, with the majority of taVNS research focusing solely on limb function scores and neglecting to dissect the underlying neurophysiological mechanisms. There remains no consensus on taVNS stimulation parameters, including stimulation intensity, frequency, duration, and timing. The safety profile of taVNS applied to the right ear warrants further validation. Limited studies have reported lateralized effects with taVNS applied to the left ear. Future high-quality studies with larger sample sizes are imperative to establish optimal stimulation parameters and elucidate the mechanisms of action, thereby informing the development of the most effective taVNS treatment protocols for clinical practice.