WAVE-FORM COMPLEXITY OF UNIT-ACTIVITY RECORDED WITH CONCENTRIC NEEDLEELECTRODES FROM HUMAN PERIPHERAL-NERVES

Using standardised concentric needle electrodes 170 single units were recorded from myelinated cutaneous afferents in the human median or ul nar nerves. The unitary waveforms were of four types: single-peaked mo nophasic potentials (type I), double-peaked monophasic potentials (typ e II), biphasic potentials (type III) and triphasic potentials (type I V). Type II and IV occurred more frequently than the other types. Unit s of different functional classes had similar waveforms and there was no specific type of waveform distribution in any particular unit categ ory. In some recording situations there were changes in unitary wavefo rms from one type to another. There was a tendency for the complex typ e IV, type III and type II waveforms to change to the simple type I. A djustment of the electrode often provoked such waveform changes. The w aveform profiles and waveform changes observed during recordings with concentric needles were significantly different from those encountered with conventional tungsten electrodes, which might be due to differen ces in recording properties between the two electrodes. Possible neura l mechanisms underlying the observed waveforms and waveform transition s are discussed. In particular, our data suggest that concentric needl e electrodes record single-unit activity from myelinated fibres extrac ellularly.