A comparative study of recording procedures for motor evoked potential signals

Motor evoked potential (MEP) signals serve as an objective measure of the functional integrity of motor pathways in the spinal cord. Hence, they provide a reliable assessment of the extent of spinal cord injury (SCI). There are two methods currently being used for serial MEP recordings in rats: a low-frequency and a high-frequency method. In this paper, we compared the two methods and determined the better method for MEP recordings. We also compared the effect of two anesthetic agents- inhalational isoflurane and intraperitoneal ketamine - on the MEP signals. We found that under ketamine anesthesia, low-frequency stimulation led to more consistent results, while high-frequency stimulation required greater stimulation intensity and was prone to unwanted side-effects including excessive head twitches. We further found that isoflurane anesthesia severely depressed the MEP response for both low-frequency and high-frequency stimulation which rendered the resulting signal unusable.