Noninvasive VNS to Facilitate Excitability in Motor Cortex

The investigators aim to determine the effects of taVNS on motor cortex excitability. The hypothesis is that taVNS alone (sham rTMS + active taVNS) will induce increases in motor cortex excitability (post-stimulation compared to baseline). The investigators expect these changes will be of a lesser magnitude than those of TMS alone (active rTMS + sham taVNS) due to the indirect mechanistic approach of taVNS. Another aim is to determine whether taVNS-paired TMS is more effective at inducing cortical excitability than TMS alone, as it is hypothesized that pairing two forms of neuromodulation (active rTMS + active taVNS) will increase TMS-induced cortical excitability in the motor cortex when compared to single modality approaches (active rTMS + sham taVNS; sham rTMS + active taVNS). Furthermore, it is expected that this increase is timing sensitive, and the paired approach will induce larger TMS-induced cortical excitability compared to unpaired neuromodulation (active taVNS + active taVNS).

Inclusion criteria

• Age 18-80
• endorsing good health

Exclusion criteria

• no TMS-induced motor cortex excitability changes in response to 20Hz motor cortex rTMS
• active psychiatric or neurological disorders
• history of CNS disease, concussion, overnight hospitalization, or other neurologic sequelae, tumors, seizures, frequent or severe headaches
• metal implanted above the neck
• currently taking seizure reducing medications
• currently taking psychotropic medications
• any psychotropic medication taken within 5 half-lives of procedure time
• abuse or dependence of drugs (excluding nicotine and caffeine)
• currently taking medications that lower the seizure threshold
• taking any of the stimulants, thyroid medication, or steroids
• implanted devices/ferrous metal of any kind
• history of seizure or seizure disorder
• inability to determine motor threshold.
• Pregnant females and children under the age of 18 will be excluded for safety reasons
• No vulnerable populations or special classes of subjects will be considered for participation.