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Could different directions of infant stepping be controlled by the same locomotor central pattern generator?
1Division of Neuroscience, University of Alberta, Edmonton, Alberta T6G 2G4, Canada.
Insights
Human infants utilize the same central pattern generator (CPG) for locomotion to control walking in multiple directions. This suggests a unified neural control system for diverse human infant stepping patterns.
Area of Science:
- Developmental neuroscience
- Motor control
- Human locomotion
Background:
- Central pattern generators (CPGs) are neural circuits responsible for rhythmic motor activities like locomotion.
- Understanding CPG function in humans, particularly during early development, is crucial for deciphering motor control mechanisms.
- Previous research has primarily focused on forward locomotion, leaving the control of varied stepping directions less explored.
Purpose of the Study:
- To investigate whether a single central pattern generator (CPG) in human infants can govern locomotion in multiple directions (forward, sideways, backward).
- To analyze kinematic and electromyographic data to identify similarities and differences in stepping patterns across various directions.
- To determine if smooth transitions between stepping directions are possible, further supporting a unified CPG hypothesis.
Main Methods:
- Fifty-two infants (2-11 months) were tested on a treadmill, with their orientation adjusted to elicit forward, sideways, and backward stepping.
- Limb segment motion and surface electromyography (EMG) of lower limb muscles were recorded.
- Infants' responses to varying treadmill speeds and gradual changes in stepping direction were analyzed.
Main Results:
- Most infants capable of forward walking also demonstrated the ability to step sideways and backward.
- Stepping in different directions showed similar responses to changes in treadmill speed, with consistent relationships between stance, swing, and cycle durations.
- While some muscle activation differences were observed (e.g., hamstrings, quadriceps), no discrete changes in EMG or temporal parameters occurred during gradual directional transitions.
Conclusions:
- The findings strongly support the hypothesis that a single locomotor CPG controls diverse stepping directions in human infants.
- The ability of most infants to step in multiple directions, consistent responses to speed variations, and seamless directional transitions indicate a flexible and unified neural control system.
- This study provides significant insights into the developmental neuroplasticity of human locomotion and the underlying neural mechanisms governing movement control.
Abstract:
This study examined the idea of whether the same central pattern generator (CPG) for locomotion can control different directions of walking in humans. Fifty-two infants, aged 2-11 mo, were tested. Infants were supported to walk on a treadmill at a variety of speeds. If forward stepping was elicited, stepping in the other directions (primarily sideways and backward) was attempted. The orientation of the infant on the treadmill belt determined the direction of stepping. In some infants, we also attempted to obtain a smooth transition from one direction to another by gradually changing the orientation of the infant during a stepping sequence. Limb segment motion and surface electromyography from the muscles of the lower limb were recorded. Most infants who showed sustained forward walking also could walk in all other directions. Thirty-three of 34 infants tested could step sideways. The success of eliciting backward stepping was 69%. Most of the infants who did not meet our backward stepping criteria did, however, make stepping movements. The different directions of stepping had similar responses to changes in treadmill speed. The relationship between stance and swing phase durations and cycle duration were the same regardless of the direction of stepping across a range of speeds. Some differences were noted in the muscle activation patterns during different directions of walking. For example, the hamstrings were much more active during the swing phase of backward walking compared with forward walking. The quadriceps was more active in the trailing leg during sideways walking. In some infants, we were able to elicit stepping along a continuum of directions. We found no discrete differences in either the electromyographic patterns or the temporal parameters of stepping as the direction of stepping was gradually changed. The results support the idea that the same locomotor CPG controls different directions of stepping in human infants. The fact that most infants were able to step in all directions, the similarity in the response to speed changes, and the absence of any discrete changes as the direction of stepping was changed gradually are all consistent with this hypothesis.