MULTIPLE ACTION-POTENTIAL WAVE-FORMS OF SINGLE UNITS IN MAN AS SIGNS OF VARIABILITY IN CONDUCTIVITY OF THEIR MYELINATED FIBERS

Percutaneous microneurography was performed with concentric needle ele ctrodes to record neural activity from myelinated fibres in human peri pheral nerves. Template matching techniques were used together with in terspike interval analysis and studies on functional class, receptive field characteristics, conduction velocities and other single fibre pr operties to classify single units. Sometimes the same fibres exhibited different action potentials at the same time. The potentials had some common features, but differed either in their waveform types or only in duration. There was a correlation between the occurrence of the dif ferent potential shapes and firing frequency of the studied unit. The outcome of the studies suggested that there was a common denominator w hich could explain the observations. Most likely, momentary fluctuatio ns in excitability of the myelinated fibres occurring during the relat ive refractory period or the supernormal period were responsible for t he variations in complexity of the studied units due to a partial bloc k of fibre propagation probably caused by the recording electrode. Thu s, action potentials deriving from the same axon may not always have t he same shapes. Methods for unit classification, such as template matc hing, are discussed in the light of our findings.