Spatiotemporal organization of α‐motoneuron activity in the human spinal cord during different gaits and gait transitions

Abstract

Here we studied the spatiotemporal organization of motoneuron (MN) activity during different human gaits. We recorded the electromyographic (EMG) activity patterns in 32 ipsilateral limb and trunk muscles from normal subjects while running and walking on a treadmill (3-12 km/h). In addition, we recorded backward walking and skipping, a distinct human gait that comprises the features of both walking and running. We mapped the recorded EMG activity patterns onto the spinal cord in approximate rostrocaudal locations of the MN pools. The activation of MNs tends to occur in bursts and be segregated by spinal segment in a gait-specific manner. In particular, sacral and cervical activation timings were clearly gait-dependent. Swing-related activity constituted an appreciable fraction (> 30%) of the total MN activity of leg muscles. Locomoting at non-preferred speeds (running and walking at 5 and 9 km/h, respectively) showed clear differences relative to preferred speeds. Running at low speeds was characterized by wider sacral activation. Walking at high non-preferred speeds was accompanied by an 'atypical' locus of activation in the upper lumbar spinal cord during late stance and by a drastically increased activation of lumbosacral segments. The latter findings suggest that the optimal speed of gait transitions may be related to an optimal intensity of the total MN activity, in addition to other factors previously described. The results overall support the idea of flexibility and adaptability of spatiotemporal activity in the spinal circuitry with constraints on the temporal functional connectivity of hypothetical pulsatile burst generators.

Changes in the Spinal Segmental Motor Output for Stepping during Development from Infant to Adult

“…EMG data were high-pass filtered (40 Hz), rectified, low-pass filtered (zero-lag fourth-order Butterworth filter with cutoff at 10 Hz), time interpolated over individual gait cycles to fit a normalized 200-point time base, and averaged (Ivanenko et al, 2005b). In addition, since the cycle duration differed substantially across groups of subjects (see Fig.…”

“…In addition, since the cycle duration differed substantially across groups of subjects (see Fig. 2C), the low-pass filter in neonates was normalized relative to that of the adults (i.e., it was made inversely proportional to the cycle duration, corresponding to 3 Hz in neonates since the cycle duration was about three times longer than in adults) under the assumption that the width of the basic EMG components tends to scale with speed Cappellini et al, 2006). Data filtering does not seem to affect the overall shape of the basic temporal components .…”

“…EMG electrode placement was performed according to recommendations for minimizing cross talk from adjacent muscles (Kendall et al, 1993) and was described in detail previously . Infrared reflective markers (diameter, 1.4 cm) were attached on each side of the subject, and the kinematic data were recorded at 100 Hz by means of the Vicon 612 system with nine TV cameras spaced around the walkway (Ivanenko et al, 2005b;.…”

“…Muscle activation during infant stepping involve excessive cocontraction of many leg muscles (Forssberg, 1985;Okamoto et al, 2001;Dominici et al, 2011;Teulier et al, 2012), compared to the much more sparse muscle activation of adult walking (Winter and Yack, 1987;Ivanenko et al, 2006). Infant stepping also shares features with stepping in other mammals (Forssberg, 1985;Patrick et al, 2009), and it has been proposed that their control patterns may be similar (Yang and Gorassini, 2006;.…”

“…We used the recordings from 12 muscles in each leg to reconstruct the patterns of segmental motor output in the infant lumbosacral spinal cord, and then compared the spatiotemporal activation patterns to those in toddlers, older children, and adults. The data on the segmental nerve supply, together with the methods of mapping EMG activity to the spinal motor pools (Yakovenko et al, 2002;Grasso et al, 2004;Ivanenko et al, 2006), provide a noninvasive tool for investigating the development of the spinal segmental output in humans.…”