Beta-amyloid deposition in the medial temporal lobe in elderly non-demented brains and in Alzheimer's disease.

The density of diffuse, primitive, classic and compact beta-amyloid (beta/A4) deposits was estimated in the medial temporal lobe in elderly non-demented brains and in Alzheimer's disease (AD). In the non-demented cases, beta/A4 deposits were absent in the hippocampus but in 8/14 cases they were present in the adjacent cortical regions. Variation in beta/A4 deposition in the non-demented cases was large and overlapped with that of the AD cases. The ratio of mature to diffuse beta/A4 deposits was greater in the non-demented than in the AD cases. In both the non-demented cases and AD, the beta/A4 deposits were clustered with, in many tissues, a regular distribution of clusters along the cortex parallel to the pia. However, the mean cluster size of the deposits in the cortex was greater in AD than in the non-demented cases. These results suggest that the spread of beta/A4 pathology between the modular units of the cortex and into the hippocampus could be important factors in the development of AD.