The acoustic cortex in Alzheimer's disease.

The morphology of the acoustic cortex was studied in light and electron microscopy, in 6 post mortem cases of Alzheimer's disease. Silver impregnation techniques and routine stainings were applied for the study of the cytoarchitecture and the cellular morphology of the acoustic cortex. Samples from every part of the acoustic cortex were processed for electron microscopy. The morphological findings were correlated with those of normal controls of relevant age, as well as with the temporal isocortex of the anterior part of the superior temporal gyrus. Silver impregnation techniques revealed a marked loss of dendritic spines in the second, third and fourth cortical layers. An obvious decrease of the axonic collaterals of the large triangular and round neurons was also seen. Neurofibrillary tangles were found in the soma and the initial part of the axon in a large number of neurons, being more prominent in the neurons of the second and third cortical layers. Senile plaques were dispersed all over the acoustic cortex. Electron microscopy revealed numerous paired helical filaments (PHF) located mostly in the soma and the axons of the large neurons as well as numerous Hirano bodies. Synaptic alterations, such as polymorphism of the synaptic vesicles in the presynaptic terminals, dilatation of the synaptic cleft and accumulation of osmiophilic material in the postsynaptic terminals were seen in numerous synaptic profiles in the acoustic cortex. The rare dendritic spines developed synaptic contact practically only with one presynaptic terminal, in contrast to the normal controls which demonstrated numerous dendritic spines developing synapses with more than one presynaptic terminal. The morphological alterations in the acoustic cortex might explain the profound deficit in verbal memory and the language disturbances that are hallmarks in early cases of Alzheimer's disease.