INCLUSION CRITERIA:
To be eligible for entry into the study, candidates must meet al the following criteria:
1. Be 4 years of age or older.
2. Have simple or complex partial seizures.
3. Seizures must persist despite medical therapy.
4. Able to give informed consent, or, assent if a child.
5. Have been determined by the NINDS neurology staff to have medically intractable epilepsy.
6. Have agreed to undergo brain surgery to treat medically intractable epilepsy.
7. Have agreed to allow some of the tissue removed during the surgery to be used for research.
EXCLUSION CRITERIA:
Candidates will be excluded if they:
1. Are pregnant. (Women of childbearing age will be tested with a urine pregnancy test and will have agreed to avoid being pregnant by practicing a reliable form of contraception or by abstinence from sexual intercourse.)
2. Cannot have an MRI scan as determined by the radiologist.
3. Have a bleeding disorder that cannot be corrected before testing or treatment.
4. Are unable to understand the risks of the testing and surgical therapy. (A clinical neuropsychologist that is not an investigator for this protocol examines all patients before epilepsy surgery. She will determine if a subject is unable to understand risks, unable to reach reasonable decisions and incompetent to give informed consent.