Bergquist, Källén, and collaborators, in a series of works summarized by Bergquist & Källén (1954) have studied the early ontogenesis of the central nervous system in vertebrates including, among other problems, the development of the brain nuclei. As is apparent from these papers, nuclear development starts from so-called ‘migration areas’, i.e. parts of the ventricular wall with a high migration tendency. From these areas cells migrate either in one or in a number of successive periods, giving rise to migration layers which lie one outside the other. These layers may later become subdivided and in this way form localized cell groups or nuclear anlagen.
These studies have also shown that the formation of the nuclei takes place according to a pattern which is very much the same in different vertebrates. The position and the number of migration areas in different brain types is relatively constant.