Summary

Recent studies performed in invertebrates have challenged the classical views on the role of a neurone within a network. Indeed, it has been clearly demonstrated that a neurone can belong to different networks involved in the generation of different motor activities (Meyrand, Simmers & Moulins, 1991; Weimann, Meyrand & Marder, 1991). The activation of respiratory neurones during non-respiratory behaviours such as vomiting, coughing or swallowing suggest that such ‘multipurpose or multifunctional’ neurones might also exist in the central nervous system (CNS) of mammals.

Introduction

The neural origin of motor activities has been the interest of physiologists since the last century. During the 1960s, rapid progress took place with the development of invertebrate preparations performing complex motor tasks with few neurones organized in ‘simple’ circuitry. In parallel, vertebrate preparations permitting the study of continuing motor activities such as respiration or locomotion were developed by Cohen (1969, 1971, 1979, 1981), von Euler (1973, 1977, 1983, 1986), Sears (1964, 1971, 1990), Lund (Lund & Dellow, 1971; Lund, 1976; Lund & Enomoto, 1988), Grillner (1974, 1981, 1985) and others. As time has gone by, it has become clear that different rhythmic motor patterns result from the interaction between a neuronal network, often referred to as a central rhythm generator or central pattern generator (CPG) residing within the CNS, and afferent inputs (i.e. peripheral feedback loops) arising as the consequence of the movements themselves.