Why is frequency of epidural stimulation an important factor in facilitating locomotion?
The frequency requirement for spinal cord stimulation to produce stepping is variable among species and types of stimulation (Gerasimenko et al., 2008). In decerebrated cats, epidural stimulation produces stable stepping at 3–10 Hz (Iwahara et al., 1991; Gerasimenko et al., 2003), whereas intraspinal stimulation produces stepping at 40–60 Hz (Kazennikov and Shik, 1988). Intraspinal microstimulation in cats spinalized 5–7 d before testing produces stepping at 2–6 Hz (Barthélemy et al., 2007). The optimum frequency for initiation of rhythmic movements with epidural stimulation in human is between 30 and 40 Hz (Dimitrijevic et al., 1998; Minassian et al., 2007) and is correlated with the appearance of long-latency components in the EMG bursts (Jilge et al., 2004; Minassian et al., 2004). Although this variability in the optimum stimulation frequency for facilitating or inducing stepping can be attributed to multiple factors, our observations suggest that the specific spinal circuits activ
