A translational study of somatosensory evoked potential time-frequency components in rats, goats, and humans

Abstract

Somatosensory evoked potentials (SEPs) have been widely used to assess neurological function in clinical practice. A good understanding of the association between SEP signals and neurological function is helpful for precise diagnosis of impairment location. Previous studies on SEPs have been reported in animal models. However, few studies have reported the relationships between SEP waveforms in animals and those in humans. In this study, we collected normal SEP waveforms and decomposed them into specific time-frequency components (TFCs). Our results showed three stable TFC distribution regions in intact goats and rats and in humans. After we induced spinal cord injury in the animal models, a greater number of small TFC distribution regions were observed in the injured goat and rat groups than in the normal group. Moreover, there were significant correlations (P < 0.05) and linear relationships between the main SEP TFCs of the human group and those of the goat and rat groups. A stable TFC distribution of SEP components was observed in the human, goat and rat groups, and the TFC distribution modes were similar between the three groups. Results in various animal models in this study could be translated to future clinical studies based on SEP TFC analysis. Human studies were approved by the Institutional Review Board of the University of Hong Kong/Hospital Authority Hong Kong West Cluster (approval No. UM 05-312 T/975) on December 5, 2005. Rat experiments were approved by the Committee on the Use of Live Animals in Teaching and Research of Li Ka Shing Faculty of Medicine of the University of Hong Kong (approval No. CULART 2912-12) on January 28, 2013. Goat experiments were approved by the Animal Ethics Committee of Affiliated Hospital of Guangdong Medical University (approval No. GDY2002132) on March 5, 2018.

Keywords: animal models; chronic compression; latency; somatosensory evoked potentials; spinal cord injury; time– frequency analysis; time–frequency components; translational study.

Figure 1

Typical SEP waveforms of human, goat and rat. (A–C) SEP waveforms from a human (A), goat (B), and rat (C). The dominant SEP waveforms were simplified with recognizable N1 and P1. These SEPs had different latencies. SEP: Somatosensory evoked potential.

Figure 2

SEP time–frequency components of human, goat and rat groups. (A–C) Time–frequency component distributions from the human (A), goat (B), and rat (C) groups. The scales of the heat-map were used to express the peak power values of SEP TFCs, where hot color represents high peak power. These SEP TFCs were located in different time and frequency regions. SEP: Somatosensory evoked potential; TFC: time–frequency component.

Figure 3

Distribution patterns of SEP TFCs from normal humans, rat and goat groups. (A) Distribution difference between the human and goat groups. (B) Distribution difference between the human and rat groups. The distribution regions of the main components were marked as “M”, and the sub-TFCs were marked as “S1” and “S2”. The distribution patterns of the components in the rat and goat groups were similar to that in the human group, and the corresponding distribution regions of TFCs that appeared in both the human group and each animal group were matched with black lines. SEP: Somatosensory evoked potential; TFC: time–frequency component.

Figure 4

TFC distribution patterns comparison between normal and spinal injury model goat (A) and rat (B) groups. The distribution regions of the main components were marked as “M”, the region of sub-TFC that appeared in both the normal and injury groups were marked as “S1” and “S2”, and the other small sub-TFCs in the injury group only were marked as “S3”, “S4” and “S5”. In both goats and rats, the distribution patterns of the components in the injury groups were similar to those of the normal groups, and the corresponding distribution regions of TFCs that appeared in both the normal groups and injury groups were connected with black lines. SEP: Somatosensory evoked potential; TFC: time–frequency component.

Figure 5

Linear regression curve of main SEP TFCs between human and animals. (A–F) Linear regressions of main SEP TFCs between peak time: human and goat groups (A), human and rat groups (B); between peak frequency: human and goat groups (C), human and rat groups (D); and between peak power: human and goat groups (E), human and rat groups (F). Data points were marked as “*”, and red lines represent the regression lines. R² is the determination coefficient, which represents the fitting performance of the model. SEP: Somatosensory evoked potential; TFC: time–frequency component.