The Journal of Neurophysiology Vol. 83 No. 5 May 2000, pp. 2814-2824
Copyright ©2000 by the American Physiological Society
Could Different Directions of Infant Stepping Be Controlled by
the Same Locomotor Central Pattern Generator?
Tania
Lamb1 and
Jaynie F.
Yang1,2
1Division of Neuroscience and
2Department of Physical Therapy, University of
Alberta, Edmonton, Alberta T6G 2G4, Canada
Lamb, Tania and
Jaynie F. Yang.
Could Different Directions of Infant Stepping Be Controlled by
the Same Locomotor Central Pattern Generator?. J. Neurophysiol. 83: 2814-2824, 2000. 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.
