Inclusion criteria:

1. Medically-refractory neurologic disease amenable to therapy with deep brain stimulation including:
   1. Idiopathic Parkinson disease with motor fluctuation, dyskinesia, and/or medically refractory tremor despite optimal medical management by a movement disorders neurologist. OR
   2. Unilateral or bilateral mesial temporal lobe (hippocampal) epilepsy with complex partial, and/or secondarily generalized seizures, that is:
      • confirmed through a combination of interictal scalp EEG, ictal scalp EEG under video monitoring, ictal SPECT scanning, and/or invasive EEG monitoring
      • disabling seizure counts >2 per month documented over a 3 month period
      • refractory to at least three antiepileptic drugs given at clinically appropriate maintenance doses resulting in therapeutic plasma levels (in cases where such levels have been established for that particular drug. Drug failures because of side- effects will not be counted toward this total.
      • determined to have mesial temporal lobe epilepsy that is not amenable to resective surgery according to consensus opinion among epileptologists on our institution's multidisciplinary Epilepsy Surgery Committee
2. Mayo Clinic Deep Brain Stimulation Committee approval for bilateral deep brain stimulation therapy obtained on routine clinical grounds and without reference to this protocol.
3. Age 18 to 75.
4. Ability and willingness to provide informed consent and participate in the study protocol.

Exclusion criteria:

1. Diagnoses other than those included in #1 above.
2. Comorbid nonepileptic behavioral events or psychogenic movement disorder.
3. Medical contraindications to DBS surgery.
4. Psychiatric comorbidities not under stable medical therapy.
5. Neurodegenerative dementia (cognitive dysfunction resulting from frequent seizure activity will not be an exclusion criteria).
6. Implanted electronically active medical device with the potential to interfere with intracranial recordings (ex. pacemaker, automatic implantable cardioverter defibrillator (AICD), active vagal nerve stimulator).
7. Pregnancy; women of child-bearing potential will be required to commit to using an effective method of contraception during the entire duration of the trial. If a subject becomes pregnant despite these precautions, she will be required to report that to our center within two weeks at which point explantation of the experimental device would be an option.