The cerebral cortex of the human infant at term is complexly folded in a similar fashion to adult cortex but has only one third the total surface area. By comparing 12 healthy infants born at term with 12 healthy young adults, we demonstrate that postnatal cortical expansion is strikingly nonuniform: regions of lateral temporal, parietal, and frontal cortex expand nearly twice as much as other regions in the insular and medial occipital cortex. This differential postnatal expansion may reflect regional differences in the maturity of dendritic and synaptic architecture at birth and/or in the complexity of dendritic and synaptic architecture in adults. This expression may also be associated with differential sensitivity of cortical circuits to childhood experience and insults. By comparing human and macaque monkey cerebral cortex, we infer that the pattern of human evolutionary expansion is remarkably similar to the pattern of human postnatal expansion. To account for this correspondence, we hypothesize that it is beneficial for regions of recent evolutionary expansion to remain less mature at birth, perhaps to increase the influence of postnatal experience on the development of these regions or to focus prenatal resources on regions most important for early survival.
Figure - Comparison of evolutionary and postnatal cortical surface expansion. (A) Map of regional evolutionary cortical expansion between an adult macaque and the average human adult (right hemisphere only). Evolution expansion scale indicates how many times larger the surface area is in humans relative to the corresponding area in the macaque. (B) Map of human postnatal cortical expansion for comparison. (C) Correlation map comparing postnatal to evolutionary cortical surface expansion.
Tuesday, August 10, 2010
Similar brain cortex changes during human development and evolution
Hill et al. show that expansion of the human cortex during development involves the same brain areas that have changed the most in the evolutionary expansion from monkey to human brains. They suggest that it is beneficial for regions of recent evolutionary expansion to remain less mature at birth, perhaps to increase the influence of postnatal experience on their development.