Cortical laminar thickness and column spacing in human temporal and inferior parietal lobes: intra-individual...

Harasty, Seldon, Chan, Halliday, and Harding (2003) and Seldon (2005) have proposed a "balloon model" which suggests that myelin growth stretches the cerebral cortex, causing the cortical thickness to decrease and the columnar spacing to increase, in turn affecting the cortical capacity to differentiate afferent signals. This has been tested using temporal lobe (area TA) and inferior parietal lobule (areas PG, PF) histological specimens from human donors. The temporal and inferior parietal regions differ in ways that have never been described. Correlations between the thickness of laminae II-III and columnar spacing in lamina III within individual cytoarchitectonic areas in both hemispheres of each donor were calculated. Those in areas PG/PF are predominantly negative in both hemispheres, as predicted by the model. This is also true for the left hemisphere TA, but the right hemisphere TA shows no correlations between thickness and spacing. Comparisons of thickness and spacing between left and right hemispheres in PG/PF of each donor show no consistent direction, whereas those in TA fairly consistently show thinner laminae and wider column intervals on the left. In the left area TA, females have thinner laminae than males. Thus, intra-area predictions of the balloon model are supported in most areas, whereas the hemispheric asymmetry predictions appear to hold for TA, but not for the inferior parietal lobe.