J.Exp. Biol. (1970), S3, 255-263 255 Printed in Great Britain DIAGONAL LOCOMOTION IN DE-AFFERENTATED TOADS BY ELNORA SMITH HARCOMBE AND ROBERT J. WYMAN Biology Department, Yale University, New Haven, Connecticut 06520 {Received 2 April 1970) INTRODUCTION A major question in neurophysiology has concerned the patterning of motor output —is sensory feedback from peripheral sense organs essential in establishing sequences of muscular contractions, or is sensory information only used to modify a set pattern which is generated by the central nervous system ? Rhythmic and repetitive motor activities in several animals have been examined in attempts to answer this question (Sherrington, 1913; von Hoist, i939;Lissmann, 1946; Wilson, i96i;Ikeda&Wiersma, 1964; Roberts, 1969; Egger & Wyman, 1969). For studies of vertebrate locomotion, the classic preparation has been the ambulatory pattern of amphibians (Hering, 1893; Bickel, 1897). Gray (1939) and Gray & Lissmann (1940a, 1946a) performed a series of partial de-afferentations, and found that the more extensive de-afferentations produced greater loss of co-ordination and muscle tone. They reported that as long as one dorsal-ventral root pair was left intact the animals could maintain the basic diagonal walking sequence. However, when Gray & Lissmann examined 25 totally de-afferentated toads, they found that' no sign of ambulatory co-ordination remained' (p. 122, Gray & Lissmann, 1946a). When they left a single dorsal root intact, but cut the motor root to that segment, they found that no amount of unpatterned sensory stimulation in the segment could induce the diagonal walking sequence. Thus, their results indicated that patterned sensory information, fedback from a segment which was rhythmically stimulated by ambulation, was essential to the production of the diagonal walking pattern. Paul Weiss reported that one completely de-afferentated toad retained ' patterns of motor coordination . . . (which) maintain themselves in, qualitatively speaking—full integrity' (p. 469, Weiss, 1936a); however, he never supported his observation with additional examples. He also transplanted limbs in such a manner that the sensory feedback of a limb should be out of phase with that received by the limb in its normal position (19366, 1941 6); and found that this did not disturb the motor score for loco- motion. He concluded that properly timed sensory information was not necessary for diagonal locomotion. Thus both Weiss and Gray did inconclusive de-afferentation studies from which they drew opposite conclusions. They both tried other approaches to strengthen their conclusions. Gray (19406, 19466) demonstrated the existence of reflexes appropriate for ambulation, but did not show that they are necessary for ambulation, Weiss (19366, 1941 a, 6) performed developmental and limb transplantation experiments, but did not prove a central mechanism for the generation of the locomotor pattern. • Dedicated, in Memoriam, to Donald M. Wilson, our academic father and grandfather. He dared: in the secrets of nature, in the wildness of nature, and in man's nature. 17 EXB53