Brain Research 886 (2000) 224–236 www.elsevier.com / locate / bres Interactive report The intrinsic function of a motor system — from ion channels to 1 networks and behavior * ´ S. Grillner , L. Cangiano, G.-Y. Hu, R. Thompson, R. Hill, P. Wallen Nobel Institute for Neurophysiology, Department of Neuroscience, Karolinska Institutet, SE-171 77 Stockholm, Sweden Accepted 25 October 2000 Abstract The forebrain, brainstem and spinal cord contribution to the control of locomotion is reviewed in this article. The lamprey is used as an experimental model since it allows a detailed cellular analysis of the neuronal network underlying locomotion. The focus is on cellular mechanisms that are important for the pattern generation, as well as different types of pre- and postsynaptic modulation. This experimental model is bridging the gap between the molecular and cellular level to the network and behavioral level.  2000 Elsevier Science B.V. All rights reserved. Keywords: Locomotion; Networks; Ion channel; Modulation; Modeling; Behavior 1. Introduction mals also requires accurate foot placement. Locomo- tion can also be combined with other motor tasks. All vertebrates, without exception, depend on locomo- tion, which often is the most complex motor behavior Substantial information is now available concerning the performed in a given species. It involves the coordination neural subsystems responsible for the equilibrium control of a large number of muscles (often more than a hundred), [51,21] and for accurate foot placement during locomotion each of which is coordinated in a specific motor pattern in demanding terrain [22,36]. In this article, however, we repeated within each locomotor cycle. In principle, three will deal only with the neural machinery underlying different types of control systems are involved (see Fig. 1). propulsion. 1. The motor system which produces the propulsive movements, be it the leg movements of tetrapods or 2. The propulsive neural control system — an bipeds, wing movements of birds, or undulatory trunk overview movements of fish or snakes. 2. The postural motor system, which maintains the The propulsive system generating the stereotypic move- appropriate body orientation during ongoing locomo- ments characteristic of locomotion is composed of a tion. supraspinal part, which is responsible for the initiation of 3. The goal directed aspect of the locomotor behavior, locomotion and for maintaining a certain degree of drive to which brings the animal to the goal of the locomotor the spinal networks which generate the motor pattern episode, while avoiding all objects that may impede [30–32,37,64], be it swimming, walking or flying (see Fig. the locomotion. In most cases this is achieved by 1). The spinal networks are composed of excitatory and visuomotor coordination, which in the case of mam- inhibitory interneurons which activate the different groups of motoneurones in the appropriate sequence. Stimulation of two areas in the brain stem elicits locomotion by 1 activating the spinal networks [37]. One area is located at Published on the World Wide Web on 22 November 2000. the meso-pontine border and referred to as the mesence- *Corresponding author. Tel.: 146-8-728-6900; fax: 146-8-349-544. E-mail address: sten.grillner@neuro.ki.se (S. Grillner). phalic locomotor region MLR [64] and another area is 0006-8993 / 00 / $ – see front matter  2000 Elsevier Science B.V. All rights reserved. PII: S0006-8993(00)03088-2