Functional organisation and population behaviour of human peripheral nerve fibres - a microneurography study

Abstract: Functional organisation and population behaviour of human peripheralnerve fibres A microneurography study Gang Wu, M.D. From the Department of Medical Laboratory Sciences and Technology,Section of Clinical Neurophysiology, Karolinska Institute, Huddinge University Hospital,Huddinge, Sweden With regard to the intraneural organisation of peripheral nerves findings obtainedfrom previous anatomical and physiological studies appear to be controversial. Theconventional concept seems to be that peripheral nerves lack a detailed topographicalorganisation. The aim of this study was to further explore the functional arrangementof peripheral nerve fibres in humans. Microneurography was performed on healthy adult volunteers with one-surface or two-surfaceconcentric needle electrodes. Neural activity was recorded from the limb nerves. The recording properties of the electrodes were studied by performing waveform analysisof the identified unit activity. The outcome of the analyses confirmed that thistype of electrode records single unit activity from a myelinated fibre extracellularly,probably at a site where the recording surface of the electrode is close to a Ranviernode of the studied fibre. A novel interpretation to explain the occurrence of thevarious encountered unitary waveforms was proposed and reliable signal recognitionestablished. Some advantages with the concentric electrodes were specified in particularfor multichannel microneurography recordings. Four main classes of low-threshold mechanoreceptive A afferent fibres were studiedwith this technique. Their intrafascicular relationship was determined. All fourclasses of nerve fibres tended to be segregated by modality in the nerve trunk. Also,the clustered nerve fibres tended to innervate the same skin areas. In addition,population responses of mechanoreceptors belonging to the same modality were studiedand demonstrated to occur when tested with restricted electrical or tactile skinstimulation. Different unit recruitment patterns to various stimuli were revealed. Thus, earlier findings were confirmed in the present study which suggest that nervefibres are orderly organised intrafascicularly in human peripheral nerves. Populationencoding of sensory input within the nerve was commented upon in the light of thefindings. In addition, a novel hypothesis concerning intraneural nerve organisationwas proposed, namely population projection of peripheral nerve fibres. A group ofnerve fibres of the same modality innervating the same shn area is suggested to projectjointly to the brain thereby serving as a basic peripheral projection unit. Keywords: human somatosensory system, nerve organisation, peripheral nerve,cutaneous mechanoreceptors, skin innervation, microneurography, microelectrode Huddinge 1997 ISBN 91-628-2720-0