Inclusion Criteria:

• Unilateral or Bilateral Mesial Temporal lobe Epilepsy.
• Age ≥ 18 years.
• Global IQ ≥70.
• Failure of ≥ 2 AEDs approved for treatment of partial seizures, used alone or in combination at recommended dosages.
• Average ≥ 3 seizure-days per month in prior 6 months during which disabling seizures occurred. Disabling seizures are defined as complex partial seizures with or without secondary generalization, or as simple partial seizures that are noticeable by others or interfere with function.
• Ability to complete self-administered questionnaires.
• Availability of reliable collateral historian or witness.
• Patient preference for non-resective surgery, or not a candidate for mesial temporal resection.
• Give written informed consent.

Exclusion Criteria:

• Extratemporal or multifocal epilepsy.
• MRI evidence of potentially epileptogenic lesions outside the mesial temporal region.
• Lesions precluding electrode implantation (eg, vascular malformations, vascular tumors).
• Severe hippocampal sclerosis that in the surgeon's opinion precludes accurate electrode placement.
• Brain lesions that demand prompt surgical therapy (eg, malignant tumors, vascular malformations).
• Progressive neurological disorders (eg, malignant tumor, dementia, degenerative disorders).
• Medical or psychiatric conditions precluding surgery or interfering with adherence to treatment and follow-up.
• Planned pregnancy during the study. Women of child-bearing age will require a negative pregnancy test and adequate contraception methods.
• Ongoing or planned participation in other studies of new epilepsy therapies.
• Contraindication for stereotactic surgery, e.g. bleeding diathesis, anticoagulants, treatment with valproate at the time of surgery (risk of bleeding).
• Any condition that would make participation in the trial detrimental to the patient's health.