Neurons, Networks, Meeting Review and Motor Behavior

as simpler vertebrate preparations that were also ameThe International Symposium on Neurons, Networks, nable to cellular analysis (Grillner et al., 1986). At this and Motor Behavior held in Tucson, Arizona (November conference, new mammalian preparations were intro8–11, 1995) continued a 30 year tradition of once-aduced, including the neonatal rat spinal cord for studydecade meetings on motor pattern generation that highing locomotion and the brainstem slice preparation for light the major advances of the field. The first meeting, studying respiratory pattern generation. entitled “Neural Control of Locomotion,” was held in The key features of central pattern generators (CPGs) 1975 in Valley Forge, Pennsylvania (Herman et al., 1976). have now been described for a number of these model The second meeting, held in 1985 in Stockholm, was systems. In comparison, at the first meeting in 1975, more limited in scope and was called “Neurobiology of there was still discussion as to whether rhythmic behavVertebrate Locomotion” (Grillner et al., 1986). This year’s iors are generated centrally or whether such behaviors conference, organized by many of the same people who are, as Charles Sherrington had initially envisioned early organized the previous meetings (P. S. G. Stein, Washthis century, the result of chains of reflexes. As Keir ington University; S. Grillner, Karolinska Institute; A. I. G. Pearson (University of Alberta) reminded us at this Selverston, University of California, San Diego; D. G. conference, by the 1930s even Sherrington had come Stuart, University of Arizona), broadened the range, not around to the view of T. Graham Brown, that sensory only by once again including invertebrate preparations, input regulates, but is not essential in, the generation but also by including work on nonlocomotory motor of motor patterns. (Ironically, Pearson also showed us systems, such as respiration, where similar conclusions this year that in locust flight, proprioceptive input has about the cellular and synaptic mechanisms underlying more than a corrective role and is actually essential for some aspects of network organization are emerging. producing correct phasing of the basic motor pattern The common themes among the different preparations, in this preparation.) both vertebrate and invertebrate, presented at this Today, the goals of understanding motor function meeting were striking and point to thevalue of a comparhave shifted from determining merely how animals genative approach for making progress in addressing queserate behavior to, as Irving Kupfermann (Columbia Unitions of motor control. In this review, I will attempt to versity) put it, “how they do it with style.” That is, what convey some of these exciting themes. Due to the diffifeatures of motor systems allow those neuronal netculty in summing up a four day meeting in one article, works to produce flexible outputs that can deal with a I am forced to gloss over some important work that was variable environment? Thus, it is apparent that, in the presented, but readers are invited to turn to a volume last decade, the entire field has undergone an exciting associated with this meeting that is currently being preparadigm shift; instead of considering neuronal circuits pared (Stein et al., 1996). Although many people contribto be hard-wired entities, we now think of them as flexiuted to the work that I will discuss here, the convention ble networks that can be reconfigured to produce differin this paper will be to give the name of only the speaker ent outputs under varying conditions. A decade ago, who presented that work. neuromodulation of invertebrate circuits was first being This year’s gathering included a number of prominent explored (Marder, 1984); at the last meeting, reconfiguscientists formerly from the Soviet Union, whose work ration of motor networks had just been put forth by Peter did much to shape the field of motor control but who Getting (1986) as a principle of organization. Since then were prohibited by Soviet authorities from attending the the idea that neural circuits are multifunctional in this previous two conferences (including Y. Arshavsky, Unimanner has been embraced even by scientists examinversity of California, San Diego; A. G. Feldman, Univering mammalian systems. sity of Montreal; and G. Orlovsky, Karolinska Institute). It was once thought that more “complex” vertebrate It was wonderful that they were now able to participate. systems would have simpler neurons, and thus that neuThey expressed their grateful feelings at being able to romodulation of complex cellular properties such as plaattend this meeting freely and meet face to face with teau potentials and intrinsic membrane potential oscillaWestern scientists. It was, as Janis C. Weeks (University tions would be confined to invertebrates. It has now of Oregon) phrased it, “one of those moments that tranbeen demonstrated that neurons in vertebrates (includscend the science itself.” ing mammals) can be every bit as complex as inverteOne of the take-home messages of this series of conbrate neurons and can also be subject to neuromodulaferences is that the great progress which has been made tion. Even the spinal motor neuron, that supposed