Abstract
Two competing hypotheses address neuroplasticity during early brain development: the
“Kennard principle” describes the compensatory capacities of the immature developing
CNS as superior to those of the adult brain, whereas the “Hebb principle” argues that
the young brain is especially sensitive to insults. We provide evidence that these
principles are not mutually exclusive. Following early brain lesions that are unilateral,
the brain can refer to homotopic areas of the healthy hemisphere. This potential for
reorganization is unique to the young brain but available only when, during ontogenesis
of brain development, these areas have been used for the functions addressed. With
respect to motor function, ipsilateral motor tracts can be recruited, which are only
available during early brain development. Language can be reorganized to the right
after early left hemispheric lesions, as the representation of the language network
is initially bilateral. However, even in these situations, compensatory capacities
of the developing brain are found to have limitations, probably defined by early determinants.
Thus, plasticity and adaptivity are seen only within ontogenetic potential; that is,
axonal or cortical structures cannot be recruited beyond early developmental possibilities.
The young brain is probably more sensitive and vulnerable to lesions when these are
bilateral. This is shown here for bilateral periventricular white matter lesions that
clearly have an impact on cortical architecture and function, thus probably interfering
with early network building.
Keywords
brain plasticity - brain development - ontogenetic potential
