Context-dependent modulation of interlimb cutaneous reflexes in arm muscles as a

[Guest guest]

J Neurophysiol. 2006 Sep 27

Context-dependent modulation of interlimb cutaneous reflexes in arm

muscles as a function of stability threat during walking.

Haridas C, Zehr EP, Misiaszek JE.

Centre for Neuroscience, University of Alberta, Edmonton, Canada.

Cutaneous reflexes evoked in the muscles of the arms with electrical

stimulation of nerves of the foot (interlimb reflexes) are observed

during walking. These reflexes have been suggested to serve to

coordinate the actions of the legs and arms when walking is

disturbed. Recently, we showed that local cutaneous reflexes evoked

in the leg muscles after stimulation at the foot are modulated

according to the level of postural threat during walking. We

hypothesized that the amplitude of interlimb cutaneous reflexes

would similarly be modulated when subjects walk in unstable

environments. Subjects walked on a treadmill under four walking

conditions: 1) normal; 2) normal with unpredictable anterior-

posterior (AP) perturbations; 3) arms crossed; 4) arms crossed with

unpredictable AP perturbations. Interlimb reflexes evoked from

electrical stimulation of the right superficial peroneal or sural

nerve were recorded bilaterally, at four points of the step cycle.

These reflexes were compared between conditions in which the arms

were moving in a similar manner: i) normal vs. AP walking, and ii)

arms crossed vs. arms crossed with AP perturbations. Differences in

reflex amplitudes between arms crossed conditions were observed in

most upper limb muscles when subjects were perturbed while walking

compared to undisturbed walking. This effect was less apparent when

the arms were swinging freely. The results indicate the strength of

interlimb connections is influenced by the level of postural threat

(i.e. the context of the behaviour), thereby suggesting that these

reflexes serve a functional link between the legs and arms during

locomotion.