Interlimb coordination during stepping in the cat: effects of dorsal column section.

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Abstract
The effect of bilateral destruction of the dorsal columns (DC) on patterns of interlimb coordination during unrestrained overground stepping was studied by analysis of interlimb electromyograms in 9 adult cats. In intact cats, well-defined patterns of coordination of forelimb-forelimb, hindlimb-hindlimb and forelimb-hindlimb step cycles exist. Two forms of coordination of forelimb-forelimb and hindlimb-hindlimb step cycles are found: alternate and in phase. Step cycles of the forelimbs and hindlimbs are coordinated via a single trotting mode of coupling or a possible subset of this mode, diagonal couplet coordination. Pacing modes of coordination of forelimb and hindlimb step cycles are uncommon. Following bilateral lesions to the DC at T[thoracic]12, little effect on forelimb-forelimb or hindlimb-hindlimb coordination was noted, but the pattern of coordination of the step cycles of the forelimbs and hindlimbs is shifted markedly to include more frequent coupling of homolateral limbs. Lesions to the DC at C[cervical]2-3 had little effect on interlimb coordination, whether those lesions preceded or followed T12 DC sections. Fibers in the DC play a role in coordination of step cycles of the forelimbs and hindlimbs, but this does not involve the traditional DC-medial lemniscal system. Neurons traveling in the DC at T12 that leave to enter another part of the cord, before C2-3, are implicated, and may include secondary DC neurons, dorsal spinocerebellar tract neurons and dorsal long propriospinal neurons.

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