Shifting patterns of bilateral coordination and lateral dominance in the leg movements of young infants.

Patterns of interlimb coordination and lateral preference of spontaneous leg kicks were described for 8 normal human infants observed biweekly from 2 to 26 weeks of age. Newborn infants showed a high percentage of alternating movements, which were often supplanted by unilateral movements between 1 and 4 months. Simultaneous (in-phase) kicks matured later than alternating kicks. No consistent lateral preferences were detected. The developmental course was marked by variability and discontinuities within each infant. We propose that asynchronous and asymmetrical maturation of subcortical tracts and/or muscle strength could account for these behavioral shifts.