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Journal of Neuroscience, Vol 9, 488-496, Copyright © 1989 by Society for Neuroscience
Interruptions of fictive scratch motor rhythms by activation of cutaneous flexion reflex afferents in the turtle
SN Currie and PS Stein
Department of Biology, Washington University, St. Louis, Missouri 63130.
A low-spinal immobilized turtle displays a fictive scratch reflex in
hindlimb muscle nerves in response to mechanical stimulation of specific
regions of the shell (Robertson et al., 1985). There are 3 forms of the
scratch reflex: the rostral, the pocket, and the caudal; each exhibits
rhythmic activation of hindlimb motor neurons. Cutaneous stimulation of the
distal hindlimb elicits a fictive flexion reflex that exhibits tonic
excitation of hip protractor (flexor) motor neurons and tonic inhibition of
knee extensor motor neurons (Stein et al., 1982). In the present study, we
describe the motor pattern blends that resulted from transient activation
of either the ipsilateral or the contralateral flexion reflex pathway
during ongoing scratch motor patterns. Two types of blends were observed:
(1) insertions of a flexion reflex synergy into an interrupted scratch
cycle and (2) deletions of parts of a scratch cycle. Associated with each
type of motor pattern blend was a permanent reset of the ongoing scratch
rhythm. The sign of the reset (phase-advance or phase-delay) could be
predicted for all forms of the scratch based on the location of the foot
stimulus (ipsi- or contralateral) and its timing relative to the hip
protractor/retractor cycle. The timing of knee extensor activity within the
hip cycle is different for each form of the scratch (Robertson et al.,
1985); thus, the sign of the reset cannot be predicted from the timing of
the stimulus relative to the knee extensor cycle. These results indicate
the importance of the hip rhythm in determining the overall timing of the
scratch reflex.(ABSTRACT TRUNCATED AT 250 WORDS)
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