Neural regulation of rhythmic arm and leg movement is conserved across human locomotor tasks

Abstract

It has been proposed that different forms of rhythmic human limb movement have a common central neural control ('common core hypothesis'), just as in other animals. We compared the modulation patterns of background EMG and cutaneous reflexes during walking, arm and leg cycling, and arm-assisted recumbent stepping. We hypothesized that patterns of EMG and reflex modulation during cycling and stepping (deduced from mathematical principal components analysis) would be comparable to those during walking because they rely on similar neural substrates. Differences between the tasks were assessed by evoking cutaneous reflexes via stimulation of nerves in the foot and hand in separate trials. The EMG was recorded from flexor and extensor muscles of the arms and legs. Angular positions of the hip, knee and elbow joints were also recorded. Factor analysis revealed that across the three tasks, four principal components explained more than 93% of the variance in the background EMG and middle-latency reflex amplitude. Phase modulation of reflex amplitude was observed in most muscles across all tasks, suggesting activity in similar control networks. Significant correlations between EMG level and reflex amplitude were frequently observed only during static voluntary muscle activation and not during rhythmic movement. Results from a control experiment showed that strong correlation between EMG and reflex amplitudes was observed during discrete, voluntary leg extension but not during walking. There were task-dependent differences in reflex modulation between the three tasks which probably arise owing to specific constraints during each task. Overall, the results show strong correlation across tasks and support common neural patterning as the regulator of arm and leg movement during various rhythmic human movements. The innate capacity for generation of rhythmic movement patterns is found across the animal kingdom (Orlovsky et al. 1999). Humans produce a variety of rhythmic motor patterns during all forms of terrestrial and aquatic locomotion by way of walking, running, cycling, crawling, creeping and swimming. Considerable overlap with shared neurons and reorganization of synaptic activity to produce different rhythmic motor patterns with similar neuronal ensembles is well documented in invertebrate preparations such as the crayfish (Hooper & DiCaprio, 2004). A contribution to rhythmic motor outputs by spinal central pattern-generating elements (CPGs) has been suggested in many species, including humans (see for review Rossignol, 1996;Dietz, 2003;Zehr & Duysens, 2004;Yang et al. 2004;Rossignol et al. 2006). Using the research model of the infant walking paradigm, Yang and colleagues have shown that multiple locomotor tasks, including forward and backward walking and side-stepping, are probably controlled by the same reconfigured CPGs (Lamb & Yang, 2000).We previously suggested that an estimate of the probable contributions of CPG activity can be evaluated by the phase-dependent modulation of reflex amplitudes evoked during rhyth...

Modular control of varied locomotor tasks in children with incomplete spinal cord injuries

“…In humans, evidence of consistent muscle timing and interlimb coordination across varied tasks also suggests neural mechanisms used to control a variety of locomotor tasks may be similar (Lamb and Yang 2000;Patrick et al 2008;Wannier et al 2001;Zehr 2005;Zehr et al 2007). …”

“…Modular output is associated with biomechanical features of walking and remains consistent even when factors such as gait speed and body weight support are varied Ivanenko et al 2004). Furthermore, modular output associated with walking can explain muscle activation during other locomotor tasks such as recumbent stepping and arm and leg cycling Zehr et al 2007). Similar modular control across locomotor tasks further suggests the underlying neural mechanisms are similar (d'Avella et al 2003;Tresch et al 1999).…”

Paresthesias as Reflection of the Lateral Asymmetry of Neural Function in Human

“…However, some other findings strongly suggested the role of peripheral factors in rapid movements performed with hands what partly contradict models and theories based www.intechopen.com on hands performance asymmetries as an effect of exclusively central motor control (Jaric, 2000). In neurophysiologic studies it was hypothesized that the motor laterality may reflect differentially lateralized activation in the motor control system influenced by a central information processing (hemispheric specialization) and also by other structures and processes on levels of motor control such as locomotor's centers of limbs performance (CPGs) and spinal cord (Francis & Spiriduso, 2000;Schaal, 2004;Aziz-Zadeh et al, 2006;Knikou, 2007;Olex-Zarychta & Raczek, 2008;Zehr et al, 2004Zehr et al, , 2007. All these findings suggest the neural plasticity to be involved in the motor control system in human.…”

“…Cooperation with patient before, during and after the laboratory session is crucial for obtaining proper results of neurophysiologic testing taking into consideration influence of patient-dependent factors as an emotional state, any voluntary movement or even a motivation or attitude towards procedures (Kimura, 2001;Misiaszek 2003;Zehr et al, 2004Zehr et al, , 2006Zehr et al, , 2007. Before neurophysiologic testing, especially the bilateral one and in healthy participants careful screening of handedness/footedness should be provided, in order to detect any possible factor influencing the asymmetry of future results.…”

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“…(unloading reflex) -71 -7A Zehr common core 18) locomotorlike McCrea and Rybak CPG common core 8,10,12,28 ) …”