Protracted development of motor cortex constrains rich interpretations of infant cognition.

Researchers routinely use motor behaviors (e.g., eye, face, and limb movements) to index cognition in the human neonate. When developmental researchers use infant movements to index cognition, they often assume that the cortex is involved in producing the behavior. However, cortical control of movement is absent at birth, emerging gradually over the first several postnatal months and beyond; before cortical outflow emerges, brainstem networks produce complex motor behavior. Thus, cortical control of the motor behaviors used to infer cognition in neonates is not neurobiologically plausible. Researchers should be cautious when making claims about developmental continuity between newborn and adult cognition (i.e., 'core knowledge') and its supporting neural architecture. Cognition in preverbal human infants must be inferred from overt motor behaviors such as gaze shifts, head turns, or reaching for objects. However, infant mammals – including human infants – show protracted postnatal development of cortical motor outflow. Cortical control of eye, face, head, and limb movements is absent at birth and slowly emerges over the first postnatal year and beyond. Accordingly, the neonatal cortex in humans cannot generate the motor behaviors routinely used to support inferences about infants' cognitive abilities, and thus claims of developmental continuity between infant and adult cognition are suspect. Recognition of the protracted development of motor cortex should temper rich interpretations of infant cognition and motivate more serious consideration of the role of subcortical mechanisms in early cognitive development. [ABSTRACT FROM AUTHOR]