Minicolumn thinning in temporal lobe association cortex but not primary auditory cortex in normal human ageing.

The cerebral cortex undergoes changes during normal ageing with increasing effect on cognition. Disruption of minicolumnar organization of neurons is found with increased cognitive impairment in primates. We measured the minicolumn spacing and organization of cells in Heschl's gyrus (primary auditory cortex, A1), the Planum Temporale (Tpt, BA22), and middle temporal gyrus (MTG, BA21) of 17 normally aged human adults. Age-associated minicolumn thinning was found in temporal lobe association cortex (Tpt and MTG) but not primary auditory cortex (HG). Minicolumn thinning was also associated with greater plaque load, although this effect was present in all areas. The regional variability of age-associated minicolumn thinning reflects the regionally selective progression of tangle pathology in Alzheimer's Disease (AD). The generalized effect of plaque load persists when controlling for age. Therefore plaque load combines with age to increase minicolumn thinning, which may reflect increasing risk of AD. Since old age is the greatest risk factor for dementia, the transition to dementia may involve an extension of normal ageing processes.