Adaptation of Cutaneous Stumble Correction When Tripping Is Part of the Locomotor Environment

Abstract

Haridas C, Zehr EP, Misiaszek JE. Adaptation of cutaneous stumble correction when tripping is part of the locomotor environment. J Neurophysiol 99: 2789 -2797, 2008. First published April 16, 2008 doi:10.1152/jn.00487.2007. We recently showed that cutaneous reflexes evoked by stimulating the superficial peroneal (SP; innervates foot dorsum) nerve are modulated according to the level of postural threat. Context-related modulation was observed mainly in contralateral (c) responses but not in the ipsilateral responses. This lack of effect on ipsilateral (i) cutaneous reflexes might have been caused by the general nature of the whole body perturbation. We therefore hypothesized that context-relevant mechanical perturbations applied to the dorsum of the foot by an instrumented rod at early swing during walking would produce differences in ipsilateral cutaneous reflex amplitudes, consistent with the functional relevance of the SP nerve in stumble correction responses. Subjects walked on a motorized treadmill under four conditions: 1) normal, 2) normal with mechanical perturbations at the foot dorsum, 3) arms crossed, and 4) arms crossed with mechanical perturbations at the foot dorsum. Electrical stimulation of the SP nerve was delivered at five phases of the step cycle, and cutaneous reflexes were compared between all conditions for each phase of the step cycle. Reflex responses were generally found to be modulated in amplitude during walking conditions in which mechanical perturbations were delivered, particularly in ipsilateral tibialis anterior (iTA), which showed a marked reduction in inhibition. The results indicated cutaneous reflexes in iTA and contralateral medial gastrocnemius (cMG) were influenced by the threat of a trip, induced by applying mechanical perturbations to the foot dorsum during walking. This task-related gating of cutaneous reflexes was not generalized to all muscles, thus suggesting a functional role in the maintenance of stability during locomotion. I N T R O D U C T I O NSpinal reflexes during human locomotion have been widely studied and have been shown to change in amplitude during walking (reviewed in Zehr and Stein 1999). Specifically, reflexes in the muscles of the legs evoked from electrical stimulation of cutaneous nerves in the foot are modulated according to the phase of the step cycle (Duysens et al. 1992;Van Wezel et al. 1997;Yang and Stein 1990;Zehr et al. 1997) as well as the task being performed (Duysens et al. 1993;Komiyama et al. 2000). Both Zehr et al. (1997) and Van Wezel et al. (1997) observed cutaneous reflexes in the muscles of the leg with electrical stimulation of the superficial peroneal (SP; innervating the dorsum of the foot) nerve during walking. During swing phase, SP nerve stimulation elicited a suppression of ankle flexor activity and excitation of the proximal muscles of the leg. These responses in the muscles were associated with a reduction in dorsiflexion and an increase in knee flexion. The authors suggested the evoked response was representative of a "st...

Modulation of Cutaneous Reflexes From the Foot During Gait in Parkinson's Disease

“…Similar results can be obtained with mechanical perturbation of the swing phase (Dietz et al 1986;Schillings et al 2000). A perceived threat to stability has been shown to affect crossed reflex responses (Haridas et al 2005(Haridas et al , 2008. Thus in agreement with colleagues (2005, 2008) it is proposed that the currently described cBF activations reflect the facilitation of reflex pathways that are commonly recruited in cases of perceived instability (such as when ipsilateral perturbations threaten stability).…”

“…Inversely, activation of the cortex through transcranial magnetic stimulation facilitates the reflex responses, indicating that there is convergence of the corticospinal tract and the reflex pathways involved in these responses, in confirmation of evidence obtained in cat studies (Bretzner and Drew 2005). These results prompted the suggestion that the cortical input may act to selectively change the gain in these reflex pathways (Haridas et al 2005(Haridas et al , 2008. It was found that conditions that posed a threat to stability during gait (such as walking with arms crossed when surface translations of the belt of the treadmill could occur) selectively increased the amplitude of responses in contralateral muscles (Haridas et al 2005).…”

“…Similar results were obtained when an added postural threat was induced by unexpectedly touching the dorsum of the foot during walking (Haridas et al 2008). It was speculated that these crossed reflexes were facilitated from the motor cortex to restore balance in case of instability (Haridas et al 2005(Haridas et al , 2008. Down-regulation (decreased response amplitudes) can occur as well.…”

“…It was found that conditions that posed a threat to stability during gait (such as walking with arms crossed when surface translations of the belt of the treadmill could occur) selectively increased the amplitude of responses in contralateral muscles (Haridas et al 2005). Similar results were obtained when an added postural threat was induced by unexpectedly touching the dorsum of the foot during walking (Haridas et al 2008). It was speculated that these crossed reflexes were facilitated from the motor cortex to restore balance in case of instability (Haridas et al 2005(Haridas et al , 2008.…”

“…Walking on a treadmill can be seen by PD patients as a threat to stability. Thus one might expect an exaggeration of responses, especially on the contralateral side (Haridas et al 2005(Haridas et al , 2008). …”