Abstracts

Rationale: Gelastic seizures are typical semiological features of hypothalamic hamartomas but they also occur in temporal or frontal lobe epilepsy cases, therefore suggesting that they could admit different origin within a large network involved in laughter. We aimed to identify which brain structure or group of brain structures subserve epileptic laughing behavior in epilepsy surgery candidates submitted to stereoelectroencephalographic (SEEG) recordings. Methods: Fifteen patients were included in the study, 12 from Grenoble University Hospital, France, and 3 from Bucharest University Hospital, Romania. Mean age at presurgical work up was 30.6 years and mean age at seizure onset was 13.6 years. Magnetic resonance imaging (MRI) showed different kind of lesions in 10 cases, including a hypothalamic hamartoma (HH) in 2 patients, and was negative in 5. A total number of 52 seizures with laughter were SEEG-recorded, of which 9 were elicited by intracranial electrical stimulation. We then selected one representative seizure for each patient and plotted superimposed on the patient's MRI the position of SEEG electrodes that displayed a low voltage fast activity at seizure onset, as well as SEEG electrodes that were involved when the laughing behavior occurred. Other clinical symptoms and signs associated with laughter were also evaluated using hierarchical cluster analysis. Results: The seizure onset zone (SOZ) was located in the frontal lobe in 7 cases, in the temporal lobe in 5, in the HH in 2, and in the parietal opercular cortex in 1 patient. Mean seizure duration was 49.7 seconds and laughing occurred with a mean delay of 9.8 seconds after the SEEG seizure onset. In 11 cases laughing behavior was an early clinical sign during their seizures. In 10 cases (66%), laughter correlated with a multilobar involvement including mainly the temporo lateral and orbitofrontal structures, irrespective of SOZ location. Seizures that arose from the dorsolateral or mesial frontal cortices disrupted a more extended network related with laughter, that also included the orbitofrontal region. Focal intralesional discharges were associated with laughter in the 2 patients with HH. The hierarchical cluster analysis revealed that psychomotor arrest, grimacing, eye deviation, facial blushing, auras, oroalimentary automatisms, gestural automatisms,hypermotor behaviours, breathing difficulties and loss of conscioussness, were reaching a higher than 0.5 association coefficient with laughter. Loss of consciousness was common during gelastic seizures not related to HH. Conclusions: Laughter is an epileptic manifestation that occurs in seizures of various cortical origins, and it is related to the ictal involvement of complex interconnected brain networks. However, the orbitofrontal cortex might play the role of a common relay, irrespective of SOZ location.