Introduction

In the mid 1960s, a rare collection of normal human peripheral nerves obtained from healthy volunteers came from Chile to the Institute of Neurology in London. The material awaited further examination and quantitation by electron microscopy, which was eventually accomplished under the direction and unfailing support of W.G.P. Mair (Ochoa & Mair, 1969a, b). At that time, all we had at hand were reproductions of human unmyelinated fibres originally drawn by Remak, and micrographs of silver stains of unmyelinated axons obtained by Ranson and later by Gasser. We learned that, in man, unmyelinated fibres exhibit a specific fine structure and are 4 times more abundant than myelinated fibres. Unmyelinated fibres drop out with age and in disease. Under those circumstances the surviving axons produce tiny sprouts which make their calibre spectrum bimodal.

Basic electrophysiology

Zotterman, the impetuous Swedish scientist who first recorded impulse activity in unmyelinated (C) fibres in animals, often credited Hallin and Torebjörk with being the pioneer investigators who first recorded propagated impulse activity in C-fibres in humans (Hallin & Torebjörk, 1970; Torebjörk & Hallin, 1970). The equally outstanding work from Belgium, by Van Hees & Gybels (1972), came at about the same time. Through the use of the microneurographic technique of Hagbarth and Vallbo (Hagbarth & Vallbo 1967; Vallbo & Hagbarth, 1968), Swedes and Belgians managed to obtain single-unit recordings of C-fibre activity from undissected nerves of awake human subjects, and described receptor–response properties of C polymodal nociceptors supplying human skin.