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Transient disturbances to one limb produce coordinated, bilateral responses during infant stepping
J F Yang1, M J Stephens, R Vishram
1Department of Physical Therapy, University of Alberta, Edmonton T6H 2G4, Canada.
Insights
Infants
Area of Science:
- Neuroscience
- Developmental Biology
- Biomechanics
Background:
- Infant motor control is crucial for developing independent walking.
- Understanding how infants adapt to unexpected challenges informs developmental theories.
- Comparative analysis with mammals and adults provides evolutionary insights.
Purpose of the Study:
- To investigate infant responses to transient limb disturbances during treadmill stepping.
- To compare infant motor adaptations with those of lower mammals and adult humans.
- To elucidate the neural control mechanisms underlying infant locomotion stability.
Main Methods:
- Transiently stopping lower limb motion during the swing phase in infants (3-10 months).
- Applying external load to the pelvis during the stance phase.
- Analyzing changes in stepping parameters (stance/swing phase duration) and electromyogram (EMG) activity.
- Comparing responses across different load conditions and developmental stages.
Main Results:
- Infants prolonged the stance phase and delayed swing onset in response to limb disturbances.
- The degree of motor adaptation correlated with the load experienced by the contralateral limb.
- Added pelvic load significantly altered gait parameters but did not increase extensor EMG amplitude.
- Responses showed organized adjustments conducive to maintaining equilibrium and forward progression.
Conclusions:
- Infant stepping circuitry exhibits organized responses to external perturbations.
- These responses are essential for maintaining balance and forward movement during locomotion.
- The findings contribute to understanding the development of motor control and adaptability in humans.
Abstract:
Transient disturbances were applied to the lower limbs of infants (3-10 mo of age) while they were supported to stepped on a treadmill. The aim was to determine how stepping infants respond to novel disturbances that would disrupt equilibrium during independent walking. Their responses were also compared with those from lower mammals and adult humans. In the first series of experiments, the motion of the limb in the swing phase was transiently stopped by the experimenter grasping the limb for a short time (0.1-1.7 s). During such disturbances, the stance phase was prolonged in the contralateral limb, and the onset of the swing phase was delayed. The degree to which the stepping was modified in the contralateral limb depended on the amount of load experienced by that limb. If the contralateral limb was bearing very little weight at the time of the disturbance, its rhythm did not change appreciably. In the second series of experiments, load was added to the infant by pushing down on the pelvis during the stance phase. This greatly prolonged the stance phase and delayed the swing phase. It did not increase the amplitude of the extensor electromyogram (EMG) of the loaded limb. In conclusion, the neural circuitry controlling stepping in the infants responds to disturbances in an organized fashion that is conducive to maintaining equilibrium and forward progression.