EM study of the numbers of cortical synapses in the brains of ageing people and people with Alzheimer-type dementia.

Numbers of synapses were counted in columns of neuropil orientated at right angles to the pia in frontal and temporal regions from postmortem brains. In the frontal region of 28 patients aged 26-90 years there were 1.2 X 10(8) mm3 (SD 0.03 X 10(8], and in the temporal of 18 patients aged 16-90 years there were 1.4 X 10(8) mm3 (SD 0.04 X 10(8]. Regression analysis showed a statistically significant (P less than 0.01) decrease with age for the frontal region but not the temporal. Four patients had been clinically diagnosed as suffering from Alzheimer-type dementia and had neurofibrillary tangles and numerous senile plaques in the cortex. The numbers of synapses in these four patients did not differ from the remaining apparently intellectually normal people.