Neurophysiological Characterization of a Non-Human Primate Model of Traumatic Spinal Cord Injury Utilizing Fine-Wire EMG Electrodes

Abstract

This study aims to characterize traumatic spinal cord injury (TSCI) neurophysiologically using an intramuscular fine-wire electromyography (EMG) electrode pair. EMG data were collected from an agonist-antagonist pair of tail muscles of Macaca fasicularis, pre- and post-lesion, and for a treatment and control group. The EMG signals were decomposed into multi-resolution subsets using wavelet transforms (WT), then the relative power (RP) was calculated for each individual reconstructed EMG sub-band. Linear mixed models were developed to test three hypotheses: (i) asymmetrical volitional activity of left and right side tail muscles (ii) the effect of the experimental TSCI on the frequency content of the EMG signal, (iii) and the effect of an experimental treatment. The results from the electrode pair data suggested that there is asymmetry in the EMG response of the left and right side muscles (p-value < 0.001). This is consistent with the construct of limb dominance. The results also suggest that the lesion resulted in clear changes in the EMG frequency distribution in the post-lesion period with a significant increment in the low-frequency sub-bands (D4, D6, and A6) of the left and right side, also a significant reduction in the high-frequency sub-bands (D1 and D2) of the right side (p-value < 0.001). The preliminary results suggest that using the RP of the EMG data, the fine-wire intramuscular EMG electrode pair are a suitable method of monitoring and measuring treatment effects of experimental treatments for spinal cord injury (SCI).

Keywords: fine-wire intramuscular EMG electrode; linear mixed model; non-human primate model; relative power; traumatic spinal cord injury; wavelet transform.

Figure 1

Graphical representation of the raw electromyography (EMG) signal.

Figure 2

Wavelet analysis; decomposition and reconstruction steps.

Figure 3

Data Structure: The data in this work was collected from the left (L) and right (R) side of the tail for five subjects during multiple experiment days (d1, d2, …, dn) for (pre- and post-lesion period). The data of each day was decomposed into seven frequency sub-bands (D1, D2, D3, …, A6). Three of the subjects received a combination of treatment (Treatment group); the remaining two subjects did not receive any treatment post-lesion (Control group).

Figure 4

The estimated mean of the relative power (RP) of seven reconstructed EMG sub-bands prior to the creation of traumatic spinal cord injury (TSCI) for the left and right side of the tail. Of note for each band, there is a difference in RP value when compared to the left and right side of the tail. The D2 sub-band of the left and right side has the maximum RP, and the significant difference between the two sides is at the D1, D2, D4, and D5 sub-bands. The star indicates a significant difference.

Figure 5

The estimated mean of the RP of seven reconstructed EMG sub-bands prior and post to the creation of TSCI for the left side of the tail. Of note, the RP values for the frequency sub-bands (D4, D6, and A6) are significantly higher in the post-lesion period. The star indicates a significant difference.

Figure 6

The estimated mean of the RP of seven reconstructed EMG sub-bands prior and post the creation of TSCI for the right side of the tail. Of note, the RP values for the lower frequency sub-bands (D4, D6, and A6) are significantly higher in the post-lesion period, while the higher frequency sub-bands (D1 and D2) are significantly lower in the post-lesion period. The star indicates a significant difference.

Figure 7

The estimated mean of the RP of seven reconstructed EMG sub-bands post-lesion for the treatment (Tr) and the control (Ctrl) groups of the left side; of note, the RP values for the frequency sub-bands (D1, D2, D3, and D6) are significantly different. Subjectively, the distribution of the RP in the treatment group is similar to the RP distribution in the pre-lesion period for all the subjects. The star indicates a significant difference.

Figure 8

The estimated mean of the RP of seven reconstructed EMG sub-bands post-lesion for the treatment (Tr) and the control (Ctrl) group of the right side; of note, the RP values for frequency sub-bands (D1, D3, D4, D5, D6, and A6) are significantly different. Subjectively, the distribution of the RP in the treatment group is similar to the RP distribution in the pre-lesion period for all the subjects. The star indicates a significant difference.