Cortical Map Plasticity as a Function of Vagus Nerve Stimulation Intensity

• Pairing a tone with moderate intensity VNS increased the A1 response to the tone.
• Moderate intensity VNS pairing was more effective than high intensity VNS pairing.
• Cortical plasticity is enhanced as a non-monotonic function of VNS intensity.

BackgroundPairing sensory or motor events with vagus nerve stimulation (VNS) can reorganize sensory or motor cortex. Repeatedly pairing a tone with a brief period of VNS increases the proportion of primary auditory cortex (A1) responding to the frequency of the paired tone. However, the relationship between VNS intensity and cortical map plasticity is not known.Objective/hypothesisThe primary goal of this study was to determine the range of VNS intensities that can be used to direct cortical map plasticity.MethodsThe rats were exposed to a 9 kHz tone paired with VNS at intensities of 0.4, 0.8, 1.2, or 1.6 mA.ResultsIn rats that received moderate (0.4–0.8 mA) intensity VNS, 75% more cortical neurons were tuned to frequencies near the paired tone frequency. A two-fold effective range is broader than expected based on previous VNS studies. Rats that received high (1.2–1.6 mA) intensity VNS had significantly fewer neurons tuned to the same frequency range compared to the moderate intensity group.ConclusionThis result is consistent with previous results documenting that VNS is memory enhancing as a non-monotonic relationship of VNS intensity.