Understanding and Optimizing Vagus Nerve Stimulation Directed Cortical Plasticity

Vagus nerve stimulation (VNS) is a tool that has been used to treat epilepsy, depression and enhance memory. In the last few years VNS has been observed to direct cortical plasticity when paired with a sensory or motor event. Now VNS is being examined as a new tool to treat tinnitus and stroke by reversing pathological brain plasticity. The VNS pairing therapy has improved several patient’s conditions who are suffering from tinnitus or paralysis from stroke. Even though several patients benefited from the VNS pairing therapy none were completely cured, and some patients had little to no benefit. One reason for this could be that the VNS parameters have not been optimized. When VNS is used to treat epilepsy, depression or to enhance memory, a certain VNS current intensity range has been beneficial to people. My study revealed that VNS-tone pairing enhances cortical plasticity over a twofold range of VNS intensity at 0.4 mA and 0.8 mA. Another VNS parameter my study looked at was the interval between nerve stimulations for the VNS-tone pairing therapy. VNS-tone pairing therapy with a longer interstimulus interval significantly increased the degree of map plasticity compared to the same stimulation with a shorter interval. These observations confirm that the interval between VNStone pairing events and intensity current influences the degree of cortical plasticity. The final parameter my experiments observed was the number of stimulations VNS-tone pairing achieved in a session. Decreasing the number of stimulation in the VNS-tone pairing did not enhance cortical plasticity.