Vagus Nerve Stimulation After Training Strengthens Motor Learning in Mice, Study Finds

Researchers at Tohoku University have found that stimulating the vagus nerve immediately after a training session helped mice retain a newly learned movement more strongly over the following days. The study, published in the journal iScience, points to a role for communication between the body's organs and the brain in shaping how motor skills become long-term memories.

The vagus nerve carries sensory information from internal organs to the brain and relays brain signals that help regulate functions such as heart rate and digestion; vagus nerve stimulation (VNS) is already used to treat several disorders. To test its effect on learning, the researchers fitted a small cuff electrode around the left cervical vagus nerve of mice and trained them on a task called horizontal optokinetic response (HOKR), in which the eyes track moving visual stripes, a task that depends on the cerebellum, the brain region that governs movement timing and precision.

The team delivered VNS only after each training session, not during practice, so it produced no immediate improvement in performance. Instead, stimulated mice showed stronger learning on later days, indicating that VNS acted on the processes that preserve a movement memory after practice rather than on performance in the moment. "The key point is that VNS was delivered only after training," said Professor Ko Matsui. "VNS may open a hidden window of opportunity for enhanced learning by making the brain environment more receptive to long-lasting change."

Using fiber photometry, the researchers measured blood volume near the cerebellar flocculus, the brain area involved in this learning task. A single train of VNS produced a two-stage vascular response, with blood volume briefly dropping before rising, and repeated stimulation created rhythmic oscillations in local blood volume. Mice with larger oscillations tended to learn more strongly by the fifth day, suggesting VNS may aid memory consolidation by reshaping the metabolic environment around the affected brain circuits.

"Our brains may be more strongly influenced by the body than we imagine," said lead author Junyu Chen. The work was conducted in mice, so it does not yet show that post-training stimulation would improve learning in humans; the researchers plan to refine the timing and pattern of stimulation and further examine how these vascular rhythms contribute to long-term learning.