Inclusion Criteria:

   - Patients with a clinical diagnosis of medically refractory epilepsy with partial onset
   seizures suitable for implantation with the VNS Therapy System.

   - Patients willing to undergo an EMU evaluation for a period of at least three days with
   activation of the AMM feature during that time.

   - Patients must be at least 12 years old.

   - Patients must be in good general health and ambulatory.

   - Patient or guardian must be willing and able to complete informed consent/assent.

Exclusion Criteria:

   - Patients have had a bilateral or left cervical vagotomy.

   - Patients 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 patient.

   - Patients expected to require full body magnetic resonance imaging (MRI).

   - Patients have a history of implantation of the VNS Therapy.

   - Patients with an IQ known or estimated to be < 70, history of depression requiring
   hospitalization, or suicidality as defined by DSM IV-TR that in the investigator's
   judgment would pose an unacceptable risk for the patient or prevent the patient's
   successful completion of the study.

   - Patients with a history of status epilepticus within 1 year of study enrollment.

   - Patients with known clinically meaningful cardiovascular arrhythmias as well as
   patients with clinically meaningful cardiovascular arrhythmias determined by a 24-hour
   Holter recording obtained during the baseline period.

   - Patients dependent on alcohol or narcotic drugs as defined by DSM IV-TR within the
   past 2 years.

   - Patients with a history of psychogenic non-epileptic seizures.

   - Women who are pregnant. Women of childbearing age must take a pregnancy test and agree
   to use an approved method of contraception during the study.

   - Patients currently enrolled in another investigational study.