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The Journal of Neurophysiology Vol. 86 No. 2 August 2001, pp. 1026-1036
Copyright ©2001 by the American Physiological Society
Department of Zoology, University of Oklahoma, Norman, Oklahoma 73019
Berkowitz, Ari
Rhythmicity of Spinal Neurons Activated During Each Form of
Fictive Scratching in Spinal Turtles. J. Neurophysiol. 86: 1026-1036, 2001. Are behaviors that rely on common
muscles and motoneurons generated by separate or overlapping groups of
pattern-generating neurons? This question was investigated for the
three forms of scratching in immobilized, spinal turtles. Individual
neurons were recorded extracellularly from the gray matter through most of the spinal cord hindlimb enlargement gray matter, but were avoided
in the region of motoneuron cell bodies. Each form of fictive
scratching was elicited by mechanical stimulation of the body surface.
The rhythmic modulation of spinal neurons was assessed using phase
histograms and circular statistics. The degree of rhythmic modulation
and the phase preference of each rhythmically active neuron were
measured with respect to the activity cycle of the ipsilateral hip
flexor nerve. The action potentials of rhythmic neurons tended to be
concentrated in a particular phase of the ipsilateral hip flexor
activity cycle no matter which form of fictive scratching was elicited.
This consistent phase preference suggests that some of these neurons
may contribute to generation of the hip rhythm for all three forms of
scratching, strengthening the case that vertebrate pattern-generating
circuitry for distinct behaviors can be overlapping. The degree of
rhythmic modulation of each unit during fictive scratching was
consistently correlated with the dorsoventral location of the
recording, but not with the mediolateral or rostrocaudal location;
neurons located more ventrally tended to be more rhythmic. The phase
preferences of units were related to the region of the body surface to
which each neuron responded maximally (i.e., the region to which each unit was broadly tuned). Units tuned to the rostral scratch or pocket scratch region tended to have a phase preference during ipsilateral hip flexor activity, whereas units tuned to the caudal scratch region did not. This suggests the hypothesis that the hip
flexes further during rostral and pocket scratching, and extends further during caudal scratching, due to the net effects of a population of spinal interneurons that are both broadly tuned and
rhythmically active.
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