This study evaluates whether a non-invasive brain stimulation technique called Temporal Interference (TI) can reduce epilepsy-related abnormal brain activity and influence sleep-related brain rhythms in adults with focal drug-resistant epilepsy undergoing stereo-EEG monitoring for clinical care. Up to 30 participants will complete stimulation sessions during wakefulness and, when possible, natural non-REM sleep. Brain activity will be recorded using scalp EEG and implanted sEEG electrodes before, during, and after TI stimulation. Some participants may also receive subthreshold direct stimulation through implanted electrodes for comparison. The study aims to determine whether TI can reduce epilepsy biomarkers, alter sleep-related brain activity, and compare favorably with conventional direct electrical stimulation while remaining within established safety limits.