Developmental plasticity: to preserve the individual or to create a new species?

The cerebral cortex has an amazing capacity to adjust its organization in response to perturbations of its normal development. This developmental plasticity can be considered to have, as its ultimate goal, the preservation of an 'intact' individual, capable of integrating sensory information to generate an adequate behavioural response. The mechanisms underlying developmental plasticity, however, can also be considered of importance to generate variability among individuals of the same species and, as such, create the platform for evolution to occur. Here I describe three experiments that alter the configuration of the somatosensory cortex of the mouse. The first is based on the removal of whisker follicles neonatally and demonstrates that the formation of barrels is dependent of the presence of follicles. The second is based on results of selective inbreeding for the number of sensory organs (whisker follicles) and illustrates the strong tendency during the period of developmental plasticity to preserve the internal organization of the cerebral cortex. The third experiment is based on a mutation that affects the formation of barrels and, as a consequence, alters cortical processing of sensory information. This mutation can be considered to have resulted in an evolutionary deviation.