High-frequency oscillations in human brain

Ripples are 100-200 Hz short-duration oscillatory field potentials that hav e recently been recorded in rat hippocampus and entorhinal cortex. They ref lect fast IPSPs on the soma of pyramidal cells, which occur during synchron ous afferent excitation of principal cells and interneuron networks. We now describe two similar types of high-frequency field oscillations recorded f rom the entorhinal cortex and hippocampus of patients with mesial temporal lobe epilepsy. The first type appears be the human equivalent of normal rip ples in the rat. The second, which we have termed fast ripples (FR), are in the frequency range of 250-500 Hz. FR are found in the epileptogenic regio n and may reflect pathological hypersynchronous population spikes of bursti ng pyramidal cells. Hippocampus 1999;9:137-742. (C) 1999 Wiley-Liss, Inc.