"Specificity versus (quasi-) randomness" revisited.

Speculation on neuron connectivity in the cerebral cortex, made some ten years ago, were re-evaluated in the light of modern cross identification methods. The identification of individual neurons and their synapses, including physiological characterization, detailed light microscope analysis of the same neurons, and immunocytochemical analysis of these neurones on the light microscope level and of their synapses on the level of the electron microscope, indicate that the specificity of local neuronal connections was underestimated in the earlier studies. Although the new methods revealed a higher degree of specificity in the choice of their connections, there seems to remain ample room for epigenetic (or functionally induced) plasticity of re-arrangement in neuronal circuits during later - even in postnatal - stages of development.