Inclusion Criteria:

1. 9 years old or older

2. Diagnosis of epilepsy with focal seizures with or without focal to bilateral tonic clonic seizures (International League Against Epilepsy classification). Diagnosis established by both clinical history and an EEG consistent with focal seizures.

   Note: A normal interictal EEG is consistent with focal seizures, if other data is adequate to provide localization.

3. Epilepsy is refractory to treatment, defined as: failure to achieve adequate seizure control despite demonstrated compliance, according to medical records, on at least two (2) FDA-approved ASDs at a daily dose considered therapeutic for the patient's demographic according to package labeling, within approximately the last 3 years.
4. Seizure frequency ≥3 per month, over the past year.
5. Currently on ≥1 ASDs with no changes in antiepileptic drug doses in the 3 weeks prior to baseline visit in the study and no planned dose changes during the trial. Changes after baseline visit are permitted only if clinically necessary.
6. An MRI scan of the brain using 1.5 Tesla magnet, or greater, with T1, T2, and FLAIR sequences, performed within past 3 years and more recently than any craniotomy or skull burr hole procedure.
7. Seizure focus that allows design of an appropriate stimulation montage. Note: Seizure focus can be identified within a lobe, or 2 adjacent lobes. Identification of the border of the seizure focus can be approximate (+/- 2 gyri).
8. Available seizure history and supporting data
9. All female study subjects of child-bearing age are required to have a pregnancy test. Additionally, all females of childbearing potential will be required to use an effective method of birth control (defined as having a documented failure rate of <=1%; for women using enzyme-inducing ASDs hormonal contraceptives will not be considered as effective).
10. Written informed consent obtained from study subject or subject's legal representative and ability for study subject to comply with the requirements of the study.
11. Assent from pediatric subjects when appropriate.

Exclusion Criteria:

1. Presence of a condition or abnormality that in the opinion of the Investigator would compromise the safety of the subject or the integrity of the data.
2. Evidence for more than one seizure focus. (NOTE: For this study, a seizure focus is defined as a cortical region confined to one hemisphere and either one lobe or on a junction of two adjacent lobes from which seizures arise , as documented by scalp or intracranial EEG, that is either supported or not refuted by MRI, and either supported or not refuted by clinical semiology). If the interictal EEG is normal, a seizure focus may be identified by the combination of structural findings on MRI and clinical signs/symptoms associated with the subject's seizures.
3. Seizure focus is one of: interhemispheric, cingulate, or orbitofrontal
4. Seizure focus is hemispheric or poorly defined
5. History of psychogenic nonepileptic seizures in past 2 years, or physiologic nonepileptic seizures and non-epileptogenic events, including suspicion for or a significant history of syncope, and any non-epileptic events must be clearly differentiable from subject's focal seizures based on previously recorded video EEG showing distinct clinical and electrographic features of the subject's PNES compared to their epileptic seizures.
6. Seizures of generalized onset
7. Status epilepticus in the last 12 months
8. Presence of any disease, medical condition or physical condition that, in the opinion of the Investigator, may compromise interfere, limit, affect or reduce the subject's ability to complete a study of 24 weeks duration
9. Presence of any disease, medical condition or physical condition that, in the opinion of the Investigator, may adversely impact the safety of the subject or the integrity of the data.
10. Damaged skin on scalp that may interfere with tDCS stimulation.
11. Pregnant or unwilling to practice birth control during participation in the study.
12. Nursing mothers.
13. Any cranial metal implants (excluding ≦1 mm thick epicranial titanium skull plates and dental fillings) or medical devices (i.e. cardiac pacemaker, deep brain stimulator, medication infusion pump, cochlear implant). Note: Vagus nerve stimulator (VNS) is allowable if the device is in MR Mode (e.g. switched off) during tDCS stimulation and the VNS device is MR conditional.
14. Previous surgeries opening the skull leaving skull defects capable of allowing the insertion of a cylinder with a radius greater or equal to 5 mm.
15. A history of addiction to, dependence on, abuse of, misuse of, distribution of, or use of any illicit substance.

Note: Other protocol defined Inclusion/Exclusion Criteria may apply.

Eligibility last updated 6/27/2024. Questions regarding updates should be directed to the study team contact.