Research on animals and in humans has shown that a specific part of the brain, the thalamus, may control certain types of seizure activity; and that if this area of the brain receives electrical stimulation, fewer seizures may occur or the seizures may be less severe. This multicenter, prospective, randomized, double-blind, parallel design clinical trial will evaluate the safety and effectiveness of this treatment.

The study will last a total of 13 months. There is an initial 12-week baseline phase when participants will be seen every four weeks. At these visits routine medical tests will be performed and data will be collected to help determine and confirm eligibility to participate in the study. If, at the end of baseline, a participant continues to meet certain criteria and qualifies, he or she will be scheduled for the implant surgery within 14 days after the last visit of the baseline phase. Four weeks after the surgery, the 12-week blinded phase will begin. At this visit, we will randomly assign participants to either the active stimulation group or the control (no stimulation) group.

After completing the 12-week blinded phase, an unblinded phase will begin for an additional nine months when all participants will receive active stimulation. When the unblinded phase ends, participants will be seen for long-term follow-up once every six months until either the device is approved or the study ends.

You may be eligible if you:

• Men and women between the ages of 18 and 65 years
• Partial onset seizures with or without secondary generalization
• Anticipated average of six or more partial-onset seizures per month during the baseline phase, with no more than 30 days between seizures during the baseline phase
• Failed at least three antiepileptic drugs due to lack of efficacy

This is a partial list of eligibility requirements.