Cepeda C, Levinson S, Nariai H, et al. - Since pathological high-frequency oscillations (HFOs), especially fast ripples (FRs, > 250 Hz), were pathognomonic of an active epileptogenic zone, however, the origin of FRs remains unknown, researchers analyzed the association between FRs recorded with intraoperative preresection electrocorticography (ECoG) and spontaneous synaptic activity recorded ex vivo from cortical tissue samples resected for the treatment of pharmacoresistant epilepsy. Participants in the study were 47 children (ages 0.22–9.99 yr) with focal cortical dysplasias (CD types I and II), tuberous sclerosis complex and non-CD pathologies. Regardless of the pathological substrate, FR-positive regions showed significantly higher sIPSC frequencies relative to FR-negative regions. In comparison, in both regions, the frequency of sEPSCs was similar. Such findings indicate that increased GABA synaptic activity in pediatric epilepsy patients is correlated with interictal FRs in the epileptogenic zone and suggest that GABAergic interneurons play an active role in the formation of pathological HFOs. Increased GABA synaptic activity may help to dampen excessive excitability of cortical pyramidal neurons in the epileptogenic zone, but it could also promote neuronal network synchrony.