Spinal and Supraspinal Control of the Direction of Stepping during Locomotion

Abstract

Most bipeds and quadrupeds, in addition to forward walking, are also capable of backward and sideward walking. The direction of walking is determined by the direction of stepping movements of individual limbs in relation to the front-to-rear body axis. Our goal was to assess the functional organization of the system controlling the direction of stepping. Experiments were carried out on decerebrate cats walking on the treadmill with their hindlimbs, whereas the head and trunk were rigidly fixed. Different directions of the treadmill motion relative to the body axis were used (0°, ±45°, ±90°, and 180°). For each direction, we compared locomotion evoked from the brainstem (by stimulation of the mesencephalic locomotor region, MLR) with locomotion evoked by epidural stimulation of the spinal cord (SC). It was found that SC stimulation evoked well-coordinated stepping movements at different treadmill directions. The direction of steps was opposite to the treadmill motion, suggesting that this direction was determined by sensory input from the limb during stance. Thus, SC stimulation activates limb controllers, which are able to generate stepping movements in different directions. By contrast, MLR stimulation evoked well-coordinated stepping movements only if the treadmill was moving in the front-to-rear direction. One can conclude that supraspinal commands (caused by MLR stimulation) select one of the numerous forms of operation of the spinal limb controllers, namely, the forward walking. The MLR can thus be considered as a command center for forward locomotion, which is the main form of progression in bipeds and quadrupeds.

Interfacing a salamander brain with a salamander-like robot: Control of speed and direction with calcium signals from brainstem reticulospinal neurons

“…3G). Such activation is consistent with the MLR being a structure generating symmetrical locomotor movements in lampreys [41], salamanders [30], and cats [51]. When a selective microinjection of 0.27 to 1.89 pmol of D,L-glutamate (2.5 mM, 3-5 pulses, 2 Hz, 3-4 PSI, 20-50 ms pulses, 0.11-0.76 nL per injection) over the right mRN was superimposed to MLR stimulation, we observed an increased RS Ca 2+ response ipsilaterally to the injection site (Fig.…”

Defining pacing quantitatively: A comparison of gait characteristics between pacing and non-repetitive locomotion in zoo-housed polar bears

“…The decreased variance displayed in the pacing step cycles resembles locomotory behavior produced by decerebrate mammals with no functional nervous tissue in higher brain centers including the cerebral cortex (Armstrong, 1988;Goulding, 2009;Hiebert and Pearson, 1999;Musienko et al, 2012). These animals therefore lack descending input, which normally modifies output from neuronal networks within the spinal cord known as central pattern generators, or CPGs, to coordinate locomotion (Duysens and Van de Crommert, 1998).…”

Translation of the rat thoracic contusion model; part 2 — forward versus backward locomotion testing

“…11 Although these locomotion patterns are rather basic and require externally provided full weight-and balance-support, they do indicate that segmental spinal circuitry required for conscious backward and forward locomotion is likely very similar or even identical. This suggests that the difference between backward and forward locomotion after SCI is not so much because of differences in lumbar spinal circuitry but rather because of differences in the requirement of supraspinal control.…”

“…Backward locomotion is hypothesized to be more specific for supraspinal, voluntary and conscious locomotion as brainstem stimulation in decerebrated quadrupeds was only able to elicit forward, but not backward, walking patterns. 11 As a reference, severe SCI animals were included, myogenic motor-evoked potentials (MMEPs) to transcranial electrical motor cortex stimulation were measured, and locomotion ability was scored with the widely used Basso, Beattie, Bresnahan (BBB)-locomotor scoring method. 2,12 To objectify some of the key, but arguably subjective, locomotor features of the BBB score, the single frame analysis and catwalk gait analysis were used.…”