Abstract
In primates, cortical regions appear to be heterogenous in terms of their quantitative characteristics. The present study explored the development of these cortical regions by quantifying the basilar dendritic systems of lamina V pyramidal neurons across four regions of human neonatal cortex. Brain tissue was removed from the left hemisphere of four neurologically normal infants, representing each region of Benson’s (1994) hierarchically arranged cortical processing model (low-integrative regions: primary areas, Brodmann’s area (BA) BA4 and BA3-1-2, and unimodal area, BA18; high-integrative association region: supramodal area BA10). Tissue was stained with a modified rapid Golgi technique. Ten cells/region (N = 160) were quantified using a Neurolucida computer system (Microbrightfield Inc., Baltimore MD). Cells were evaluated for total dendritic length, mean segment length, dendritic segment count, dendritic spine number, and dendritic spine density. A nested MANOVA design (SAS System for Windows, Cary, v. 8.0) revealed that dendritic complexity varied significantly across cortical regions, exhibiting a stepwise pattern across hierarchically arranged areas (BA4 > BA3-1-2 > BA18 > BA10). To investigate potential heterochronous developmental trends across these cortical regions, infant dendritic patterns were compared to those in adults, which exhibit a considerably different stepwise ordering of complexity, with BA10 being consistently more complex than the other regions. Overall, regional dendritic patterns suggest that cortical development is hierarchically organized by functional regions, with the dendritic systems of primary cortical regions developing first, followed by unimodal and supramodal association areas, the latter being ultimately more complex in the adult.