Possible contributions of CPG activity to the control of rhythmic human arm movement

Abstract

There is extensive modulation of cutaneous and H-reflexes during rhythmic leg movement in humans. Mechanisms controlling reflex modulation (e.g., phase- and task-dependent modulation, and reflex reversal) during leg movements have been ascribed to the activity of spinal central pattern generating (CPG) networks and peripheral feedback. Our working hypothesis has been that neural mechanisms (i.e., CPGs) controlling rhythmic movement are conserved between the human lumbar and cervical spinal cord. Thus reflex modulation during rhythmic arm movement should be similar to that for rhythmic leg movement. This hypothesis has been tested by studying the regulation of reflexes in arm muscles during rhythmic arm cycling and treadmill walking. This paper reviews recent studies that have revealed that reflexes in arm muscles show modulation within the movement cycle (e.g., phase-dependency and reflex reversal) and between static and rhythmic motor tasks (e.g., task-dependency). It is concluded that reflexes are modulated similarly during rhythmic movement of the upper and lower limbs, suggesting similar motor control mechanisms. One notable exception to this pattern is a failure of contralateral arm movement to modulate reflex amplitude, which contrasts directly with observations from the leg. Overall, the data support the hypothesis that CPG activity contributes to the neural control of rhythmic arm movement.

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.…”

“…Despite the detail neural mechanisms involved in motor control are still unknown, the multidimensional and temporal regulation of limb mechanics by spinal circuits is assumed to be attached to neural proprioreceptive feedback from muscles and sensory receptors as well as to organization of descending command and motor output from the spinal cord. (Christou et al, 2002;Kimura, 2001;Rothwell, 1996;Zehr 2002Zehr , 2004Zehr & Wolpaw, 2006;Misiaszek, 2003;Olex-Zarychta et al, 2009;Olex-Zarychta, 2010). One of the most extensively studied reflexes in the literature on human neurophysiology is a Hoffmann reflex (H-reflex).…”

“…The relative ease with which this reflex can be elicited in muscles throughout the human body and few neural parameters involved in this circuit makes it a very attractive research tool in motor control research (Misiaszek, 2003;Zehr & Wolpaw, 2006). Studies incorporating the H-reflex as a neural probe showed changes in excitability of the reflex occur while movement actions and also in the absence of movement what suggests the existence of intrinsic modulating factors in motor control system, connected with the spinal circuit organization and/or with transmission parameters in motor and sensory pathways (Aymard et al, 2000;Kimura, 2001;Misiaszek, 2003;Zehr et. al, 2004;Zehr, 2006;Zehr et.al., 2007).…”

“…The selective hemispheric activation may thus play a role in the motor output asymmetry in human extremities. Assuming that the afferent sensory feedback is the neural basis for interlimb coordination and contributes strongly to the modulation of the spinal reflexes as well as control on supraspinal levels (Freitas et al, 2007;Pearson and Gordon, 2000;Rothwell, 1996;Zehr et al, 2004;Zehr, 2006), it was hypothesized that the functional dominance in limbs may be an important modulating factor for the motor coordination (Olex-Zarychta & Raczek, 2008;Olex-Zarychta, 2010). Earlier studies indicated asymmetries in the number of corticospinal axons (Nathan et al, 1990) as well as in cortical representations of the dominant limb muscles (Nudo, 1992) and brought evidences supporting the adaptive plasticity in muscle and cutaneous afferent reflex pathways induced by training and rehabilitative interventions.…”

“…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.…”