Analysis of the EEG dynamics of epileptic activity in gelastic seizures using decomposition in independent components Alberto J.R. Leal a,b, * , Ana I. Dias b , Jose ´ P. Vieira b a Department of Neurophysiology, Hospital Ju ´lio de Matos, Av a do Brasil, No. 53, 1749-002 Lisbon, Portugal b Department of Pediatric Neurology, Hospital Dona Estefa ˆnia, Lisbon, Portugal Accepted 16 March 2006 Abstract Objective: Gelastic seizures are a frequent and well established manifestation of the epilepsy associated with hypothalamic hamartomas. The scalp EEG recordings very seldom demonstrate clear spike activity and the information about the ictal epilepsy dynamics is limited. In this work, we try to isolate epileptic rhythms in gelastic seizures and study their generators. Methods: We extracted rhythmic activity from EEG scalp recordings of gelastic seizures using decomposition in independent components (ICA) in three patients, two with hypothalamic hamartomas and one with no hypothalamic lesion. Time analysis of these rhythms and inverse source analysis was done to recover their foci of origin and temporal dynamics. Results: In the two patients with hypothalamic hamartomas consistent ictal delta (2–3 Hz) rhythms were present, with subcortical generators in both and a superficial one in a single patient. The latter pattern was observed in the patient with no hypothalamic hamartoma visible in MRI. The deep generators activated earlier than the superficial ones, suggesting a consistent sub-cortical origin of the rhythmical activity. Conclusions: Our data is compatible with early and brief epileptic generators in deep sub-cortical regions and more superficial ones activating later. Significance: Gelastic seizures express rhythms on scalp EEG compatible with epileptic activity originating in sub-cortical generators and secondarily involving cortical ones. q 2006 International Federation of Clinical Neurophysiology. Published by Elsevier Ireland Ltd. All rights reserved. Keywords: Epilepsy; Hypothalamus; Hamartoma; ICA; Gelastic; Seizures 1. Introduction Gelastic seizures are a rare type of epileptic manifes- tation where laughter spells occur without a concomitant sense of joy. They are usually brief (less than 1 min) and can occur several times daily. Historically, these seizures have been associated with hypothalamic hamartomas (List et al., 1958), and more recent invasive EEG recordings demonstrated the existence of paroxysmal activity limited to the hamartoma during such events (Munari et al., 1995). Nevertheless cases have been reported where no hypothalamic lesions could be found (Arroyo et al., 1993) and this suggested the existence of extra-hypothalamic generators. In previous studies, we used source analysis techniques of the interictal spike activity of patients with hypothalamic hamartomas to demonstrate the existence of deep generators in the neighborhood of the lesion (Leal et al., 2002) and also that the EEG scalp topography can show frontal or temporal dominance depending on the particular anatomy of the connection of the hamartoma to the hypothalamus (Leal et al., 2003). The scalp EEG recordings during the seizures have not been very informative (reviewed in Munari et al., 2000) because no clear paroxysmal activity is usually found and the poor signal to noise ratio of such recordings has prevented more detailed analysis. Nevertheless visual Clinical Neurophysiology 117 (2006) 1595–1601 www.elsevier.com/locate/clinph 1388-2457/$30.00 q 2006 International Federation of Clinical Neurophysiology. Published by Elsevier Ireland Ltd. All rights reserved. doi:10.1016/j.clinph.2006.03.020 * Corresponding author. Address: Department of Neurophysiology, Hospital Ju ´ lio de Matos, Av a do Brasil, No. 53, 1749-002 Lisbon, Portugal. Tel.: C351 969851734; fax: C351 217819809. E-mail address: a.leal@netcabo.pt (A.J.R. Leal).