Vagus Nerve Stimulation After Practice Makes Skills Stick Longer in Mice, Tohoku Study Finds
Stimulating the nerve after training, not during it, strengthened learning on later days and produced rhythmic blood-volume swings in the cerebellum.
Zapping a nerve that runs from the neck to the organs may help the brain lock in a new skill, according to a study in mice from Tohoku University in Japan.
The paper, published Aug. 25 in iScience, found that stimulating the vagus nerve after each training session strengthened long-term motor learning. The stimulation did not help during training itself. Its effect showed up on later days, which points to a role in consolidation, the process by which the brain turns a fresh experience into a lasting memory.
The researchers fitted mice with a small cuff electrode on the left cervical vagus nerve. They then tested the animals on horizontal optokinetic response learning, an eye-movement task that depends on the cerebellum. In it, mice learn to track moving visual stripes better with practice. The stimulation was delivered after each training session, not while the animal was performing the task.
Mice that received post-training stimulation showed significantly stronger learning on subsequent days than those that did not. The team also found a physical signature of the effect. A single burst of stimulation produced a two-phase change in blood volume near the cerebellar flocculus, first a decrease and then a rise. Repeated stimulation produced rhythmic oscillations in blood volume in that region.
The size of those oscillations tracked performance. Mice with larger vascular oscillations tended to do better by day five, an association that suggests the rhythmic changes help create a brain environment favorable to lasting change. That would be a mechanism beyond the neurotransmitter systems usually credited with vagus nerve effects.
"VNS may open a hidden window of opportunity for enhanced learning," said Ko Matsui, who led the research, describing the idea that the brain is especially receptive just after practice.
Consolidation is the reason practice spaced over days often works better than cramming. The Tohoku team set out to test whether a body-to-brain signal could be used to strengthen that window.
The findings come with obvious limits. The work was done in mice on a single cerebellum-dependent task, and an association between blood-volume oscillations and better learning does not prove that one causes the other. Whether similar timing would help people learn a musical instrument, a sport or rehabilitation exercises after a stroke is untested in this study.
Vagus nerve stimulation is already used in humans for epilepsy and depression. The authors suggest that, if the effect holds up, timing stimulation to the minutes after training could eventually inform ways to improve skill acquisition.
