On peripheral control mechanisms acting on the central pattern generators for swimming in the dogfish.

When sinusoidal movements were artificially imposed on the tail region of the curarized spinal dogfish during "fictive locomotion' the coordinated burst pattern recorded in the ventral roots was effectively entrained to follow movement frequencies above as well as below the resting rate. The entrainment was characterized by: (1) a broad range of effective movement frequencies and amplitudes (down to a few degrees); (2) frequency-dependent timing of entrained bursts to the movement; (3) constant burst durations at low and moderate frequencies; (4) incomplete entrainment in response to high or low movement frequencies combined with a low amplitude; (5) entrainment was still present when mean position of movement was displaced laterally; (6) effects persisted when the tail region was devoid of skin and muscle tissue. Entrainment effects may be explained by the activation of stretch receptors on either side of the vertebral column-spinal cord, exciting the presumed central pattern generators (CPGs) in the hemisegments ipsilateral to the stretch, while inhibiting the contralateral CPGs.