Paper recordings of ultrafast frequencies in experimental epilepsy.

Digital EEG technology has facilitated the recording of fast activity above 50 Hz, but previous work carried out in this field is, commonly, no longer referred to in the literature. This paper presents a summary of our experience in experimental epilepsy when frequencies above 100 Hz were recorded. It was shown that conventional recordings (1-70 Hz) do not correlate with the onset of clinical seizures and can actually lead to misleading neurophysiologic conclusions. Ultrafast activity (100-1500 Hz), on the other hand, showed excellent correlation with clinical behavior and pointed to the low brainstem for the origin of nonfocal tonic-clonic seizures. In the animal analogue of absence seizures the cortex, including cingulate gyrus, thalamus, and cerebellum, showed greater involvement than other brain structures. Ultrafast activity has a very limited electrical field, and evoked responses remain restricted to the corresponding sensory pathways. Focal penicillin administration led not only to spike generation but also to associated ultrafast frequency bursts in that area. It appears likely that ultrafast burst activity may be a better marker for focal cortical epileptogenesis than spikes or sharp waves, which can be transmitted from a distance.