(I-352) Analysis of the effect of varying vagus nerve stimulation frequency on plasticity in the motor cortex.

Introduction:: A number of neurological insults, including stroke, spinal cord injury, and traumatic brain injury result in chronic impairments in motor function. It is widely held that approaches that facilitate synaptic plasticity in spared networks after a neurological injury can promote recovery. Vagus nerve stimulation (VNS) paired with rehabilitation has emerged as one such approach. VNS elicits an increase in the release of plasticity-inducing neuromodulators which results in an increase in the cortical representation of areas activated during the paired task. As such, increasing the amount of plasticity could yield an increased degree of recovery.

Previous studies have indicated an "inverted-U" relationship between the different stimulation parameters of VNS and the degree of plasticity observed. This study seeks to further establish the "inverted-U" response for the frequency of stimulation while identifying the VNS frequency that results in the greatest enhancement of plasticity when delivered during a simple jaw training paradigm.



Materials and Methods: :.
Rats received 20Hz, 30Hz, and 45Hz of VNS concurrent with chewing. Preliminary findings indicate that higher stimulation frequencies may yield a larger increase in jaw movement representation, consistent with a greater degree of plasticity. The behavioral task implemented in this study involves training the rats to chew sugar pellets retrieved from their training booth while pairing the chewing with VNS.
After 5 days of VNS paired training, the rats undergo intracortical microstimulation (ICMS) where different movement representations in the motor cortex are assessed and used to create a map with the aim of quantifying the total plasticity observed. The primary goal of conducting ICMS is to compare the total jaw area representation across the groups and determine if there are any differences in plasticity observed.





Results, Conclusions, and Discussions: :
The jaw training task presents a faster approach to testing the different stimulation parameters for vagus nerve stimulation as compared to the injury models previously used. Subsequently, the results of this study could confirm 30Hz as the optimal stimulation frequency for VNS or depict other frequencies of stimulation yielding higher amounts of plasticity, which translates into a greater degree of recovery in injured subjects. Alternatively, the results of this study could show a plateau effect where stimulation frequencies close to 30Hz could yield similar amounts of plasticity.
The results of this study will help further establish the optimal stimulation parameters for VNS and depict the importance of delivering VNS at the right frequency when used in conjunction with rehabilitation therapy.

Acknowledgements (Optional): :

References (Optional): :