Cortical contribution to scalp EEG gamma rhythms associated with epileptic spasms.

The cortical contribution for the generation of gamma rhythms detected from scalp ictal EEG was studied in unique cases of epileptic spasms and a review of the related literature was conducted. Ictal scalp gamma rhythms were investigated through time-frequency analysis in two cases with a combination of focal seizures and spasms and another case with spasms associated with cortical dysplasia. In the two patients with combined seizures, the scalp distribution of ictal gamma rhythms was related to that of focal seizure activity. In the third patient, an asymmetric distribution of the ictal scalp gamma rhythms was transiently revealed in correspondence to the dysplasic cortex during hormonal treatment. Therefore, the dominant region of scalp gamma rhythms may correspond to the epileptogenic cortical area. The current findings have reinforced the possibility of the cortical generation of ictal scalp gamma rhythms associated with spasms. The detection of high frequencies through scalp EEG is a technical challenge, however, and the clinical significance of scalp gamma rhythms may not be the same as that of invasively recorded high frequencies. Further studies on the pathophysiological mechanisms related to the generation of spasms involving high frequencies are necessary in the future, and the development of animal models of spasms will play an important role in this regard.