Rapid changes in corticospinal excitability during force field adaptation of human walking
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Force field adaptation of locomotor muscle activity is one way of studying the ability of the motor control networks in the brain and spinal cord to adapt in a flexible way to changes in the environment. Here, we investigate whether the corticospinal tract is involved in this adaptation. We measured changes in motor-evoked potentials (MEPs) elicited by transcranial magnetic stimulation (TMS) in the tibialis anterior (TA) muscle before, during, and after subjects adapted to a force field applied to the ankle joint during treadmill walking. When the force field assisted dorsiflexion during the swing phase of the step cycle, subjects adapted by decreasing TA EMG activity. In contrast, when the force field resisted dorsiflexion, they increased TA EMG activity. After the force field was removed, normal EMG activity gradually returned over the next 5 min of walking. TA MEPs elicited in the early swing phase of the step cycle were smaller during adaptation to the assistive force field and larger during adaptation to the resistive force field. When elicited 5 min after the force field was removed, MEPs returned to their original values. The changes in TA MEPs were larger than what could be explained by changes in background TA EMG activity. These effects seemed specific to walking, as similar changes in TA MEP were not seen when seated subjects were tested during static dorsiflexion. These observations suggest that the corticospinal tract contributes to the adaptation of walking to an external force field.
KeywordsAdaptation Locomotion Transcranial magnetic stimulation
This work was supported by the Natural Sciences and Engineering Research Council of Canada (NSERC). DB received a Post-Doctoral Fellowship from the Canadian Institutes of Health Research (CIHR).
- Alain S, Cantin B, Bouyer LJ (2005) Human cutaneous reflexes while walking in an elastic force field applied to the ankle. Soc Neurosci Abstr 864.12Google Scholar
- Alain S, Barthelemy D, Grey MJ, Bouyer LJ, Richards CL, Nielsen JB (2007) Rapid, task-specific modifications of cortico-spinal excitability during adaptation of human locomotion to elastic force fields applied to the ankle. Soc Neurosci Abstr 924.1Google Scholar
- Carrier L, Brustein E, Rossignol S (1997) Locomotion of the hindlimbs after neurectomy of ankle flexors in intact and spinal cats: model for the study of locomotor plasticity. J Neurophysiol 77:1979–1993Google Scholar
- Cote MP, Gossard JP (2004) Step training-dependent plasticity in spinal cutaneous pathways. J Neuro sci 24:11317–11327Google Scholar
- Jayaram G, Galea JM, Bastian AJ, Celnik P (2011) Human locomotor adaptive learning is proportional to depression of cerebellar excitability. Cereb Cortex. [Epub ahead of print]Google Scholar
- McNeil CJ, Martin PG, Gandevia SC, Taylor JL (2009) The response to paired motor cortical stimuli is abolished at a spinal level during human muscle fatigue. J Physiol 587:5601–5612Google Scholar
- Pearson KG (2000) Neural adaptation in the generation of rhythmic behavior. AnnuRevPhysiol 62:723–753Google Scholar
- Press WH (1986) Numerical recipes: the art of scientific computing. Cambridge University Press, New YorkGoogle Scholar
- Sherrington CS (1906) The integrative action of the nervous system. Charles Scribner’s Sons, New YorkGoogle Scholar
- Whelan PJ, Pearson KG (1997) Plasticity in reflex pathways controlling stepping in the cat. JNeurophysiol 78:1643–1650Google Scholar