Inclusion Criteria:

• Clinical diagnosis of medically refractory epilepsy with primary generalized tonic-clonic seizures (limited to 20 subjects) or partial onset seizures including complex partial seizures with or without secondary generalization (limited to 20 subjects).
• Must be on adjunctive antiepileptic medications.
• Willing and capable to undergo multiple evaluations with functional magnetic resonance imaging (fMRI), electroencephalogram (EEG) and electrocardiogram (ECG).
• (A) For subjects with partial onset seizures: An average of ≥ 3 countable seizures per month based on seizure diary during the 3 month baseline period and no seizure-free interval greater than 30 days during those 3 months.
• (B) For subjects with PGTCs: Have at least ≥ 3 countable seizures during the 3 month baseline period.
  • Note: Each seizure within a cluster may be counted as separate seizures.
• 18 years of age or older.
• Subject is a male or non-pregnant female adequately protected from conception. Females of childbearing potential must use an acceptable method of birth control.
• Provide written informed consent-assent/Health Insurance Portability and Accountability Act (HIPAA) authorization and self-reported measures with minimal assistance as determined by the investigator.

Exclusion Criteria:

• Currently using, or are expected to use, short-wave diathermy, microwave diathermy, or therapeutic ultrasound diathermy.
• A VNS Therapy System implant would (in the investigator's judgment) pose an unacceptable surgical or medical risk for the subject.
• A planned procedure that is contraindicated for VNS therapy.
• History of implantation of the VNS Therapy System.
• Currently receiving treatment from an active implantable medical device.
• Presence of contraindications to MRI per the MRI subject screening record.
• Known clinically meaningful cardiovascular arrhythmias currently being managed by devices or treatments that interfere with normal intrinsic heart rate responses (e.g., pacemaker dependency, implantable defibrillator, beta adrenergic blocker medications).
• History of chronotropic incompetence (commonly seen in subjects with sustained bradycardia [heart rate < 50 bpm]).
• Cognitive or psychiatric deficit that in the investigator's judgment would interfere with the subject's ability to accurately complete study assessments.
• History of status epilepticus within 1 year of study enrollment.
• Dependent on alcohol or narcotic drugs as defined by DSM IV-TR within the past 2 years, based on history. Tests for drug or alcohol use will not be administered.
• Currently being treated with prescribed medication that contains cannabis or cannabis related substance.
• Any history of psychogenic non-epileptic seizures.
• Currently participating in another clinical study without LivaNova written approval.