Spinal Cord Maps of Spatiotemporal Alpha-Motoneuron Activation in Humans Walking at Different Speeds

Abstract

Functional MRI (fMRI) imaging of motoneuron activity in the human spinal cord is still in its infancy, and it will remain difficult to apply to walking. Here we present a viable alternative for documenting the spatiotemporal maps of alpha-motorneuron (MN) activity in the human spinal cord during walking, similar to the method recently reported for the cat. We recorded EMG activity from 16 to 32 ipsilateral limb and trunk muscles in 13 healthy subjects walking on a treadmill at different speeds (1-7 km/h) and mapped the recorded patterns onto the spinal cord in approximate rostrocaudal locations of the motoneuron pools. This approach can provide information about pattern generator output during locomotion in terms of segmental control rather than in terms of individual muscle control. A striking feature we found is that nearly every spinal segment undergoes at least two cycles of activation in the step cycle, thus supporting the idea of half-center oscillators controlling MN activation at any segmental level. The resulting spatiotemporal map patterns seem highly stereotyped over the range of walking speeds studied, although there were also some systematic redistributions of MN activity with speed. Bursts of MN activity were either temporally aligned across several spinal segments or switched between different segments. For example, the center of mass of MN activity in the lumbosacral levels generally shifted from rostral to caudal positions in two cycles for each step, revealing four major activation foci: two in the upper lumbar segments and two in the sacral segments. The results are consistent with the presence of at least two and possibly more pattern generators controlling the activation of lumbosacral MNs.

An Intersegmental Neuronal Architecture for Spinal Wave Propagation under Deletions

“…As an example, neurons within populations 1, 3, and extensor motoneurons of CPG1 in Figure 5A, and the equivalent ones in the other CPG units, have a value of ϭ 0.015, which leads to an extensor phase of ϳ70 ms, whereas neurons within populations 2, 4, and flexor motoneurons, and the equivalent ones in the other CPG units, have a slightly larger value of ϭ 0.017 for which the flexor phase lasts ϳ140 ms. The constructed network generates an alternating rhythm that propagates in the rostrocaudal direction, illustrated in Figure 5B, as observed experimentally (Cuellar et al, 2009; see also Bonnot et al, 2002;Yakovenko et al, 2002;Kaske et al, 2003;Ivanenko et al, 2006;Falgairolle and Cazalets, 2007).…”

Synergy temporal sequences and topography in the spinal cord: evidence for a traveling wave in frog locomotion

“…Comparing EMG sequence and motoneuronal topography in cat and human locomotion (Yakovenko et al 2002;Ivanenko et al 2006a) suggested rostrocaudal activation with some abrupt shifts. In the rodent, rostrocaudal motoneuron activation was imaged (Bonnot et al 2002;O'Donovan et al 2008), and propagating waves were recorded in ventral roots (Cazalets 2005).…”

“…4). Because the traveling wave is a novel result that seems relevant to the temporal structure of the step cycle, we compare our model to Ivanenko et al (2004Ivanenko et al ( , 2006a where the emphasis is on temporal components at specific times in the step cycle. These were generally preserved across different forms of locomotion, with EMG differences attributed to changes in how a distribution network would channel the temporal pulses to motoneurons.…”

Biomechanics of spontaneous overground walk-to-run transition

“…Thus far, many experimental studies on the mechanics of this transition have been carried out, either using a steady protocol (steady locomotion on a treadmill with a stepwise velocity increase) (e.g. Hreljac, 1993;Raynor et al, 2002;Ivanenko et al, 2006;Hreljac et al, 2007;Prilutsky and Gregor, 2001;Ganley et al, 2011) or by imposing a constant (relatively small) acceleration on a treadmill (e.g. Thorstensson and Roberthson, 1987;Diedrich and Warren, 1995;Turvey et al, 1999;Segers et al, 2006;Segers et al, 2007a;Hreljac et al, 2007;Nimbarte and Li, 2011) or overground (e.g.…”