A light and electron microscopic study of the development of two regions of the chick forebrain.

The post hatch development of two regions of the chick telencephalon has been studied using light and electron microscopic quantitative methods. The hyperstriatum ventrale is a region known to be involved in the learning process of imprinting, and hyperstriatum accessorium is a primary telencephalic visual projection area. There were significant changes in synaptic density, neuronal density, glial cell density and in the synapse/neuron ratio in hyperstriatum ventrale. In contrast, hyperstriatum accessorium showed a greater degree of stability. The most rapid changes were seen in the immediate post-hatch period. This coincides with the period during which the critical period for imprinting lies.