ABSTRACT
It has been known for over 100 years that injury to the infant brain can have less severe consequences than similar injury in adulthood (for a review, see Finger & Almli, 1988). For example, Broca noticed in the late 1800s that damage to the speech zones of the left hemisphere during infancy did not interfere with the later development of language. It was discovered much later that this was due to the shifting of the speech zones either to the opposite hemisphere or, in some circumstances, within the left hemisphere (e.g., Rasmussen & Milner, 1977). Systematic study of the effect of early brain damage on functional development began with the studies of Margaret Kennard in the late 1930s, in which she showed that unilateral motor cortex impairments are less severe after motor cortex injury if the lesion occurs during infancy rather than adulthood (e.g., Kennard, 1942). Kennard proposed that there must be some change in the synaptic organization in the young animal that was supporting the functional recovery, although she was vague about what such changes might be. Thus, the general conclusion arising from Kennard's work was that brain injury early in life is associated with a better functional outcome than injury later because the developing brain can more easily reorganize than the adult brain. Teuber later labeled this idea the Kennard principle (Teuber, 1975), which is a term that is still often used.
