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1 Centre for Neuroscience, University of Alberta, Edmonton, Alberta, Canada
2 Department of Physical Therapy, University of Alberta, Edmonton, Alberta, Canada
3 Centre for Neuroscience, University of Alberta, Edmonton, Alberta, Canada; Department of Physical Therapy, University of Alberta, Edmonton, Alberta, Canada
* To whom correspondence should be addressed. E-mail: jaynie.yang{at}ualberta.ca.
This study examined whether human infants under the age of 12 months learn to modify their stepping pattern following repeated trip-inducing stimuli. Thirty three infants aged from 5 to 11 months were studied. The infants were held over a moving treadmill belt to induce stepping. Occasionally, a mechanical tap was applied to the dorsum of the left foot during the early swing phase to elicit a high step. In some trials, the stimulus was applied for only one step. In other trials, the foot was stimulated for a few consecutive steps. We determined whether the infants continued to show high stepping immediately after the removal of the stimuli. The results showed that after the foot was touched for 2 or more consecutive steps, some infants continued to demonstrate high stepping for a few steps after the removal of the stimuli (i.e. after-effect). Such adaptation was achieved by an increase in hip and knee flexor muscle torque, which led to greater hip and knee flexion during the early swing phase. After-effects were more commonly seen in older infants (9 months or older). The results indicated that before the onset of independent walking, the locomotor circuitry in human infants is capable of adaptive locomotor plasticity. The increased incidence of after-effect in older infants also suggests that the ability to adapt to repeated trip-inducing stimuli may be related to other factors such as experience in stepping and maturation of the nervous system.
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