VARIATION IN HIPPOCAMPAL NEURON NUMBER WITH AGE AND BRAIN VOLUME

Hippocampal size and neuron number are reduced in a number of conditio ns, including temporal lobe epilepsy and Alzheimer's disease. Furtherm ore, a decrease with advancing age has also been suggested. The presen t study examined the entire hippocampal formation of 12 subjects aged from 46 to 85 years and free from neurological disease. The volume of seven subregions (CA1, CA2-3, CA4, dentate gyrus, subiculum, presubicu lum and white matter) was determined and the number of neurons estimat ed in each of these grey matter subregions using the optical dissector technique. There was a significant relationship between CA1 neuron nu mber and cerebrum volume. Multivariate analysis showed the greater con tribution to the variance in CA1 neuron number was made by cerebrum vo lume (69%) rather than age (2%) or sex (1%). The findings of this stud y show that, in neurologically normal individuals, brain size is a maj or determinant of the number of CA1 neurons.