The basis of this project is the application of cathodal tDCS in patients with drug-resistant focal epilepsy including patients whose seizures persist after epilepsy surgery, who rejected epilepsy surgery, and/or who are not suitable for surgery. For this purpose, 5-day consecutive cathodal electrical stimulation sessions will be used with personalized electrode montage according to the patient's seizure focus. In this context, the changes in seizures frequency and epileptic discharges will be examined for the first week and 12th week after the tDCS sessions through the seizure diary of the patients and the electroencephalogram (EEG) recordings to be taken. In addition, changes in cognitive functions, mood, and quality of life will be examined in patients after the intervention.

Inclusion Criteria:

• 18 years and older,
• Diagnosed with focal epilepsy with epileptic focus determined according to clinical and electroencephalogram recordings, who have undergone epilepsy surgery but seizures persist, who refuse epilepsy surgery or who are considered unsuitable for surgery,
• Patients who comply with the definition of drug-resistant epilepsy according to ILAE (International League Against Epilepsy Classification) criteria (Patients who have failed to achieve long-term seizure-free status despite at least two appropriate antiepileptic drugs given alone or in combination),
• Minimum 1 or more seizures per month (minimum 3 months),
• No antiepileptic dose change until 3 weeks before the study, stable treatment, and no dose change planned during the study,
• At least 1.5 Tesla MR imaging was performed before the study,
• Signed the informed consent form or the consent form signed by the legal representative,
• EEG was present before the study and all EEG data was accessible,
• Cooperative patients who can speak, understand and communicate in Turkish will be recruited.

Exclusion Criteria:

• The presence of any disease/deformity in the patient that the researchers believe will affect the patient's safety or the reliability of the data to be collected,
• Detection of more than one seizure focus in the patient,
• The patient had a psychogenic non-epileptic seizure attack (Psychogenic Non-epileptic Seizures -PNES) within 2 years prior to the study,
• Having a generalized onset seizure,
• Having had status epilepticus in the last 1 year,
• Presence of any disease, medical condition, or physical condition that, according to the researchers, could prevent, limit, affect or reduce the subject's completion of a minimum period of 1 + 12 weeks,
• Tissue damage (eczema, etc.) in the area where tDCS will be applied on the skin,
• Patients who are pregnant and do not use/do not want to use contraception during the study period,
• Lactating women,
• Metal implants, fillings in the head or teeth, presence of a medical device in the body (pacemaker, deep brain stimulator, cochlear implant, nerve stimulator, etc.)
• Presence of a skull defect with a radius of 5 mm and/or larger remaining from previous surgeries,
• The patient is participating in another clinical trial.