Modularity of motor output evoked by intraspinal microstimulation in cats.
We studied the forces produced at the cat's hindpaw by microstimulation of the ipsi- and contralateral lumbar spinal cord in spinal intact alpha-chloralose anesthetized (n = 3) or decerebrate (n = 3) animals. Isometric force and EMG responses were measured at 9-12 limb configurations, with the paw attached to a force transducer and with the hip and femur fixed. The active forces elicited at different limb configurations were summarized as force fields representing the sagittal plane component of the forces produced at the paw throughout the workspace. The forces varied in amplitude over time but the orientations were stable, and the pattern of an active force field was invariant through time. The active force fields divided into four distinct types, and a few of the fields showed convergence to an equilibrium point. The fields were generally produced by coactivation of the hindlimb muscles. In addition, some of the fields were consistent with known spinal reflexes and the stimulation sites producing them were in laminae where the interneurons associated with those reflexes are known to be located. Muscle activation produced by intraspinal stimulation, as assessed by intramuscular EMG activity, was modified with limb configuration, suggesting that the responses were not fixed, but were modified by position-dependent sensory feedback. The force responses may represent basic outputs of the spinal circuitry and may be related to similar spinal primitives found in the frog and rat.
Lemay
Michel A
MA
Department of Biomedical Engineering, Case Western Reserve University, Cleveland, Ohio 44106, USA. Michel.Lemay@drexel.edu
Grill
Warren M
WM
D018686:Anesthetics, Intravenous / Q000008:administration & dosage; D000818:Animals; D018780:Body Surface Potential Mapping / Q000379:methods; D002415:Cats; D002541:Cerebral Decortication; D002698:Chloralose / Q000008:administration & dosage; D016000:Cluster Analysis; D004558:Electric Stimulation / Q000379:methods*; D004576:Electromyography / Q000379:methods; D019054:Evoked Potentials, Motor / Q000502:physiology; D007839:Functional Laterality; D006614:Hindlimb / Q000502:physiology; D007537:Isometric Contraction / Q000502:physiology*; D008124:Locomotion / Q000187:drug effects / Q000502:physiology*; D008161:Lumbosacral Region; D008297:Male; D008839:Microelectrodes; D009046:Motor Neurons / Q000502:physiology*; D018482:Muscle, Skeletal / Q000187:drug effects / Q000294:innervation / Q000502:physiology; D013116:Spinal Cord / Q000033:anatomy & histology / Q000187:drug effects / Q000502:physiology*; D013997:Time Factors
D018686:Anesthetics, Intravenous; D002698:Chloralose