THE DENSITY OF SYNAPSES AND NEURONS IN NORMAL, MENTALLY DEFECTIVE AND AGEING HUMAN BRAINS

Abstract

The densities of synapses and neurons were measured in 7 neurosurgical specimens of cerebral cortex, regarded as normal controls. The average result was 6 times 10-11 synapses/cm3, 15-6 times 10-6 neurons/cm3, and 38,000 synapses per neuron. Specimens of frontal and temporal cortex from 7 ageing brains (68 to 89 years) gave closely similar counts of neurons and synapses. Seven specimens from 3 severely retarded brains gave similar counts of neurons and slightly higher counts of synapses. A deficit of synaptic development is thus not a necessarre discussed.