ReviewThomas Graham Brown (1882–1965), Anders Lundberg (1920–), and the neural control of stepping☆
Introduction
In current reports on the neural control of terrestrial locomotion, much emphasis is placed on the capability of interneurons (INs) in the spinal segments innervating the limbs to generate the main features of the locomotor rhythm, including its flexor and extensor phases and the timing of each muscle's activity during each step. Such IN circuitry for each limb, now commonly termed a central pattern generator (CPG),1 is confined to relatively “low-level” ganglia in invertebrates and the spinal cord in vertebrates. It can express a locomotor rhythm that is not dependent upon ongoing descending input from higher centers and sensory feedback from passive and active body parts (for recent reviews, see Clarac, 2008, Clarac and Pearlstein, 2007, Grillner et al., 2008a, Grillner et al., 2008b, Orlovsky et al., 1999, Stuart, 2007a). Prior to the 1960s, the favored viewpoint was that locomotor rhythmicity was elicited by spinal reflex action2 even though evidence of a central nervous system (CNS) control component was available (Delcomyn, 1980). Such evidence was sporadic for invertebrates but quite substantial for mammals prior to 1920 as provided by Thomas Graham Brown (1882–1965) and later in the 1930s for non-mammalian vertebrates, most notably by Eric von Holst (1908–1962) and Paul Weiss (1898–1989).
In this brief historical article, we review the academic career and research accomplishments of Graham Brown (Fig. 1A), reflect on why his ideas on spinal pattern generation languished in near-total obscurity for so long, and document how his ideas were brought to the forefront of locomotion research in the 1960s by the Swedish neuroscientist, Anders Lundberg (1920–) (Figs. 1B,C).
A preliminary account of some of this material has been presented (Stuart, 2007b).
Section snippets
Graham Brown's academic career and research contributions
Graham Brown remains an enigma to modern-day movement neuroscientists. On one hand, his academic career had initial elements of success. He was the Professor of Physiology at the University of Cardiff from 1920 until 1947 and became a Fellow of the Royal Society in 1927. On the other hand, he published little of value to neuroscience after the early 1920s, had no pre- or postdoctoral trainees, and his seminal spinal locomotion work was rarely cited until the 1960s.
Anders Lundberg's academic career and research contributions
In sharp contrast to Graham Brown, Anders Lundberg's initial and subsequent research has had a profound impact on his neuroscientific peers for the full 53 years of its publication (1947–2000). Table 1 shows that throughout this period he mentored 14 PhD students and co-authored research articles with 60 other collaborators from 23 countries.13
Further developments and the current state-of-the-play on the spinal contribution to stepping
Speculation on how history may have developed had this or that not occurred is not a prominent branch of science but it is clearly of heuristic value to reflect on such issues (see, e.g., Kuhn, 1996). In this vein, what would be the current understanding of the contribution of the spinal cord to the overall control of locomotion without Graham Brown's discoveries that were certainly the primary motivation for Lundberg's work on the DOPA-released spinal locomotor network?
In attempting to answer
Acknowledgments
Some of the above was presented by D.G.S in a poster at the IBRO World Congress of Neuroscience, Melbourne, Australia, July 12–17, 2007 and at a Congress Satellite Meeting, “Motor Control at the Top End”, Darwin, Australia, July 18–21, 2007. For the preparation of our article we thank Anders Lundberg and John Bowles for providing some historical details, Rauni Larsson, Elzbieta Jankowska, and Lars-Gunnar Pettersson (together with innumerable others) for their help with Table 1, Nga Nguyen (AHSC
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H.H.'s research is supported, in part, by the Danish Medical Research Council and the Ludvig and Sara Elsass Foundation.