Multiple generators of 600 Hz wavelets in human SEP unmasked by varying stimulus rates

HUMAN scalp-derived somatosensory evoked potentials contain a high-frequenc y wavelet burst, presumably reflecting repetitive synchronized population s pikes. Here, the burst refractory behavior was characterized using median n erve electrostimulation with 18 frequencies (0.5-25 Hz) for comparison with cellular burst characteristics. Above 10 Hz only a brief high-frequency (7 00 Hz) burst component remained discernible, which gradually decreased; pos sible generators comprise cells capable of generating spike bursts of extra ordinarily high frequency, such as pyramidal 'chattering cells', cortical f ast spiking inhibitory interneurons and some thalamocortical relay cells. A t stimulation frequencies <4 Hz an additional late burst component appeared with only 494 Hz intraburst frequency. Comparably long refractory periods and low intraburst frequencies have been described for bursting cells drive n by low-threshold calcium currents. NeuroReport 10:10:1625-1629 (C) 1999 L ippincott Williams & Wilkins.