Structure of human auditory cortex. I. Cytoarchitectonics and dendritic distributions.

In the human primary and secondary auditory cortices the neuron somata are arranged in distinct columnar clusters. Measurements on their diameters and the intervals between them yield significant hemispherical differences, having in all cases greater values in the left hemisphere. Computer-assisted tracings of Golgi-impregnated dendritic trees of 300 neurons show the expected types. An analysis of the columnar structure of the dendritic trees indicates varying degrees of specificity in collecting information from their surroundings. An analysis of their tangential extent shows that in the primary cortices a greater extent in the left hemisphere effectively cancels the differences in columnar widths and intervals, allowing for a similar dendritic connectivity among columns in both hemispheres. In the secondary cortex this connectivity is greater on the right side.