This is a multi-center, randomized, blinded trial evaluating the effect of transcutaneous auricular vagal nerve stimulator (taVNS) on radiation necrosis-related cerebral edema. In this study, consenting and eligible patients will be assigned to one of two arms: treatment (Arm 1) or sham (Arm 2). Patients in both arms will have imaging performed and tissue and blood collected for assessment of changes in area of contrast enhancement and cerebral edema, inflammatory markers, and markers of blood-brain barrier permeability.

Inclusion Criteria:

• History of glioma or metastatic brain lesion previously treated with whole brain radiation, stereotactic radiation surgery, or fractionated radiation therapy
• Magnetic resonance imaging (MRI) findings consistent with possible radiation necrosis within 6 weeks prior to enrollment.
• Candidate for tissue biopsy and Laser Interstitial Thermal Therapy (LITT) ablation of the lesion
• At least 18 years of age
• If on corticosteroids, able to discontinue at least 5 days prior to start of transcutaneous auricular vagus nerve stimulation (taVNS) (Arm 1) or sham treatment (Arm 2). A stable physiologic dose of corticosteroids, if used as hormone replacement therapy, may be allowed upon discussion with the investigator. 6. Ability to understand and willingness to sign an institutional review board (IRB) approved written informed consent document. Legally authorized representatives may sign and give informed consent on behalf of study participants.

Exclusion Criteria:

• New onset neurologic deficits secondary to radiation necrosis requiring initiation of dexamethasone therapy or other intervention prior to enrollment
• Currently receiving bevacizumab for treatment of radiation necrosis or has received bevacizumab < 6 weeks prior to study enrollment.
• Currently receiving any investigational agents for treatment of radiation necrosis or has participated in a study of an investigational agent for radiation necrosis within 3 weeks prior to study enrollment.
• History of cardiac conduction disorders or presence of implanted electronic devices
• Active Crohn's disease or other inflammatory bowel disease.
• Pregnant and/or breastfeeding. Women of childbearing potential must have a negative pregnancy test within 14 days of study entry.