Semiologic and localizing value of forced thinking in focal seizures

Forced thinking is a rare ictal phenomenon characterized by the sudden intrusion of involuntary thoughts at seizure onset. Historically classified as a psychic aura and variably associated with frontal or temporal lobe epilepsy, its semiologic definition and localizing value remain debated, largely due to the scarcity of systematic studies. We conducted a retrospective review of a tertiary epilepsy center database (2005-2025) to identify patients with drug-resistant focal epilepsy presenting with forced thinking auras. Detailed semiologic analysis was performed using medical records, video-EEG data, and structured patient interviews. Presurgical evaluation findings, including scalp EEG, neuroimaging, and, when available, stereoelectroencephalography (SEEG), were reviewed to determine the epileptogenic zone. In parallel, we analyzed a large SEEG cortical stimulation database (329 patients, ∼2500 stimulations) to identify stimulation-induced forced thinking phenomena. Eight patients met the inclusion criteria. Forced thinking was consistently described as a brief, intrusive mental event occurring at seizure onset, most often with verbal content. In seven of eight patients, seizures involved the temporal lobe, predominantly the dominant (left) hemisphere; none had a purely frontal epileptogenic zone. The cohort showed a marked male predominance (7 of 8 patients). In the SEEG stimulation cohort, forced thinking was observed in only 2 patients (0.6%), all induced by temporal stimulation, with none by frontal stimulation. Forced thinking is a rare but well-defined ictal cognitive phenomenon. Our findings indicate that it is not a specific marker of frontal lobe epilepsy but rather reflects involvement of dominant temporal networks related to language and internal thought generation.