The initial phase of reflex inhibitory relaxation in extensor muscles

Thomas Graham Brown (1882--1965), Anders Lundberg (1920-), and the neural control of stepping

Thomas Graham Brown (1882--1965) undertook experiments on the neural control of stepping in the University of Liverpool laboratory of Charles Sherrington (1857--1952) in 1910--13 and his own laboratory in 1913--15 at the University of Manchester. His results revealed the intrinsic capability of the spinal cord in the guinea pig and cat to generate a stepping output pattern whose timing did not depend upon descending or sensory inputs. This idea was then revolutionary because the prevailing viewpoint was that the stepping rhythm was generated by spinal reflexes. Sadly, Graham Brown's GBR peers gave little credence to this seminal accomplishment, except perhaps Sherrington, who waxed but largely waned on the potential significance of the work. It remained for the Swedish neuroscientist, Anders Lundberg (1920-), to rescue Graham Brown's concepts from obscurity: in seminars presented in several countries between 1957 and 1980, and in widely read articles and reviews (1965--1981). Graham Brown had proposed mutually inhibitory connections between a pair of intrinsically active flexor and extensor "half-centers" on each side of the spinal cord, with the rhythmic output modulated by sensory proprioceptive input. Lundberg, Elzbieta Jankowska (1930-), and their colleagues provided seminal, compelling evidence for spinal half-center interneuronal circuitry implicated in the control of stepping and Lundberg and Ingemar Engberg (1935--2005) made behavioral EMG observations on unrestrained cats that supported a central generation of the rhythm. Subsequently, models of the spinal pattern generators for mammalian locomotion have become progressively more complex but they mostly still include a half-center component.