Introduction

Abstract

The way in which the nervous system differentiates among the various forms of sensory experience has been a central issue since the beginning of sensory physiology. A brief history of the major theories is given by Sinclair (1981). The notion of specificity of cutaneous sensation is attributed by Sinclair to Bell (1811), although it was actually Magendie (1822) who demonstrated the sensory function of the spinal cord dorsal roots. The idea of specificity of cutaneous sensation was forwarded by Müller’s doctrine of specific nerve energies (Müller, 1840–1842). Müller had in mind the Aristotelean five senses and lumped together the sensations derived from the body surface under the category of ‘touch.’ According to Sinclair (1981), Volkmann, Natanson and others in the 1840s extended the specificity concept to include the postulate of separate nerve endings for each variety of sensation arising from cutaneous stimulation. However, Sinclair emphasizes the distinction between’ specific nerve energies’ (i.e., particular nerves evoke particular sensations) and’ specific irritability’ (i.e., particular stimuli activate particular sense organs). It is one thing to show that specific stimuli preferentially activate certain sensory receptors; it is another to show that the same sensory receptors are responsible for a particular quality of sensory experience.