Epileptiform spikes and sharp waves are identified in scalp EEG recordings as transient waveforms produced by an abrupt change in voltage polarity occurring over a duration of less than 70 ms or 70–200 ms, respectively. For example, only 69 (0.5%) of 13,658 healthy candidates for aircrew training without a history of seizures had interictal spikes or sharp waves on a routine scalp EEG ( Gregory et al., 1993). Interictal spikes and sharp waves recorded from scalp EEG are a highly specific marker of epilepsy. In addition, multiple studies have now shown that HFO in the range of physiological gamma and ripple oscillations are also increased in human epileptogenic hippocampus ( Worrell et al., 2008 Crépon et al., 2010 Jacobs et al., 2010), and neocortex ( Worrell et al., 2004 Jacobs et al., 2010 Blanco et al., 2011 Schevon et al., 2009). However, recent studies reporting physiological somatosensory evoked HFO in nonhuman primates, likely reflecting multiunit cortical neuronal responses ( Telenczuk et al., 2011), makes the specific association of activity in the FR with pathology problematic. The initial studies of recordings from human hippocampus supported the hypothesis that HFO above 250 Hz, named fast ripple (FR) oscillations ( Bragin et al., 1999a, b), were a unique pathological oscillation associated with epileptic brain. In addition to interictal epileptiform spikes and sharp waves, wide bandwidth recordings from humans and animals with epilepsy have revealed high frequency oscillations (HFO) as a possible electrophysiologi-cal signature of epileptic brain. epileptiform spikes and sharp waves, that are clearly distinct from seizures and occur without clinical symptoms ( Gibbs et al., 1936 Swartz and Goldensohn, 1998 Gloor, 1969). In addition to physiological LFP it was recognized early on that human epileptic brain generates pathological interictal transients, i.e. On slower time scales (400 Hz) in sensory coding ( Baker et al., 2003 Telenczuk et al., 2011). On millisecond time scales the extracellular currents associated with single neuron action potentials are detected within a radius of ~150 μm surrounding a micro-electrode ( Buzsaki, 2004). Extracellular microwire electrodes (~10 to 50 μm) are widely used to record the neural activity spanning single neuron action potentials to collective oscillations of large neuronal assemblies ( Buzsaki, 2004). Neocortical networks that perform critical physiological functions are organized across spatial scales from sub-millimeter cortical columns to centimeter scale lobar structures. Collective neuronal oscillations of functional networks in human brain occur over a wide range of spatial and temporal scales.
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