Background: Absence epilepsy (AE) is believed to be generated by a thalamocortical network. Our laboratory showed that hippocampal neuronal firings were synchronous with the SWDs in the gamma butyrolactone (GBL) model of AE in rats. Here, we hypothesize that high frequency oscillations (HFOs) in the hippocampus and other parts of the limbic system were phase modulated by SWDs Methods: GBL (200 mg/kg i.p) was injected to induce SWDs in 6 male Long-Evans rats. Spontaneous local field potentials (LFPs) were recorded from electrodes implanted in the hippocampus and ventrolateral thalamus bilaterally and the right frontal cortex. For each LFP, modulation index (MI) gives the cross-frequency amplitude modulation of the HFOs (;90-250 Hz) by the phase of the SWD frequency at 2-8 Hz Results: Phase modulation of the HFOs by 2-8 Hz frequency increased for >45 min after GBL injection. MI increase was higher for hippocampal than thalamic LFPs, and not significant for frontal cortical LFP. MI for the nucleus accumbens LFP (N= 1 rat) also increased after GBL Conclusions: The modulation of HFOs (presumed local neural activity) by SWD frequency provides further support that the hippocampus and connected limbic system may become synchronous with the SWDs in AE