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. 2008 Jun;5(2):111-24.
doi: 10.1088/1741-2560/5/2/002. Epub 2008 Mar 26.

Hindlimb movement in the cat induced by amplitude-modulated stimulation using extra-spinal electrodes

Changfeng Tai  1 , Jicheng Wang, Bing Shen, Xianchun Wang, James R Roppolo, William C de Groat
Affiliations

Hindlimb movement in the cat induced by amplitude-modulated stimulation using extra-spinal electrodes

Changfeng Tai et al. J Neural Eng. 2008 Jun.

Abstract

Hindlimb movement in the cat induced by electrical stimulation with an amplitude-modulated waveform of the dorsal surface of the L5-S1 spinal cord or the L5-S1 dorsal/ventral roots was investigated before and after acute spinal cord transection at the T13-L1 level. Stimulation of the spinal cord or dorsal/ventral root at the same spinal segment induced similar movements including coordinated multi-joint flexion or extension. The induced movements changed from flexion to extension when the stimulation was moved from rostral (L5) to caudal (S1) spinal segments. Stimulation of a dorsal or ventral root on one side induced only ipsilateral hindlimb movement. However, stimulation on the dorsal surface of the spinal cord along the midline or across the spinal cord induced bilateral movements. The extension induced by stimulation of L7 dorsal root produced the largest ground reaction force that was strong enough to support body weight. Dorsal root stimulation induced a larger ground reaction force than ventral root stimulation and produced a more graded recruitment curve. Stepping at different speeds could be generated by combined stimulation of the rostral (L5) and the caudal (L6/L7) spinal segments with an appropriate timing between the different stimulation channels. Acute transection of the spinal cord did not change the responses indicating that the induced movements did not require the involvement of the supraspinal locomotor centers. The methods and the stimulation strategy developed in this study might be utilized to restore locomotor function after spinal cord injury.

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Figures

Fig. 1
Fig. 1
Ipsilateral left hindlimb movements induced by stimulation of individual left dorsal or ventral roots before and after spinal cord transection. Maximal stimulation intensity: 1 mA. Stimulation waveform represents the relative current levels. All stick drawings are from left camera view. The thin stick drawings show the resting position of the left hindlimb. The thick stick drawings show the maximal hindlimb movement during the stimulation.
Fig. 2
Fig. 2
Bilateral hindlimb movements induced by stimulation applied on the dorsal surface of different spinal segment (L5-S1) before (A) and after (B) spinal cord transection. Maximal stimulation intensities: 1–6 mA. Stimulation waveform represents the relative current levels. The thin stick drawings show the resting position of left or right hindlimb. The thick stick drawings show the maximal hindlimb movement during the stimulation. When no movement is induced, the hindlimb position is represented by its resting position only. In each column the left and right hindlimbs are shown as they are viewed from the left or right camera.
Fig. 3
Fig. 3
A. Four basic patterns of bilateral hindlimb movements induced by biphasic sine modulation with electrodes across each spinal segment. The thin stick drawings show the resting position of each hindlimb. The thick stick drawings show the maximal hindlimb movement during positive or negative phase of stimulation. B. Bilateral air-stepping induced by stimulation of the L6 spinal cord in a spinal intact cat. Maximum stimulus amplitude was 1 mA. Total of 60 steps (30 steps for each hindlimb) were induced during continuous 60 second stimulation. Only 6 steps are shown in this figure. Stimulation waveform represents the relative current levels.
Fig. 4
Fig. 4
Normalized ground reaction forces of the left hindlimb induced by stimulation of the left dorsal root (A and D), the left ventral root (B and E), or the left spinal cord (C and F) at L7 (○) or S1 (●) segment before (A, B, and C) and after (D, E, and F) spinal cord transection at stimulation intensity of 1–4 T. N = 4 (Cat #: 5–8).
Fig. 5
Fig. 5
A. Average thresholds for stimulation of ventral root, dorsal root, or spinal cord. * indicates statistical significance (P<0.05). N = 10. Data were from 5 cats and the thresholds for stimulation of L7 or S1 segment were plotted together. B. Ground reaction forces induced by stimulation of the L7 dorsal root at intensity of 4 T.
Fig. 6
Fig. 6
Integrating flexion and extension movements into stepping. A. Ipsilateral flexion or extension of right hindlimb induced by stimulation of right L5 or L7 dorsal root separately. B. Ipsilateral stepping (4 sec/step) of right hindlimb induced by a combined stimulation of right L5 and L7 dorsal roots. C. Ipsilateral stepping of right hindlimb at a faster speed (2 sec/step). Amplitude-modulated stimulation pulses is shown in A, but only the modulation waveforms are shown in B and C. The modulation waveforms only indicate the timing. The actual stimulation intensity was marked separately. Stimulation sites and the camera view of right hindlimb are also shown in A. The measurement of each joint angle was indicated in A on the camera view. Data are from a spinal intact cat.
Fig. 7
Fig. 7
Ipsilateral stepping of right hindlimb induced by a combined stimulation of right L5 spinal cord and L6 dorsal root after spinal cord transection. A. At a stepping speed of 4 sec/step. B. At a stepping speed of 2 sec/step. Only modulation waveforms are shown for stimulation. Stimulation sites for both A and B are shown in A. The modulation waveforms only indicate the timing. The actual stimulation intensity was marked separately. The measurement of each joint angle was indicated in Fig. 6A on the camera view.
Fig. 8
Fig. 8
Bilateral stepping induced by stimulation of L5 and L7 dorsal roots on both sides. Only modulation waveforms are shown for stimulation. The modulation waveforms only indicate the timing. The actual stimulation intensity was marked separately. The ground reaction force generated by right or left hindlimb is marked by a letter “R” or “L”. Data are from a spinal intact cat.
Fig. 9
Fig. 9
Average distances the foot traveled during the induced stepping movements in the 5 cats tested. ● - maximal foot location during extension relative to the axis passing through the hip joint. ○ - maximal foot location during flexion relative to the hip axis.
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