EVOLUTION OF THE BASAL GANGLIA IN TETRAPODS - A NEW PERSPECTIVE BASEDON RECENT STUDIES IN AMPHIBIANS

It has been postulated frequently that the fundamental organization of the basal ganglia (BG) in vertebrates arose with the appearance of am niotes during evolution. An alternative hypothesis, however, is that s uch a condition was already present in early anamniotic tetrapods and, therefore, characterizes the acquisition of the tetrapod phenotype ra ther than the anamniotic-amniotic transition. Re-examination of the BG organization in tetrapods in the light of recent findings in amphibia ns strongly supports the notion that elementary BG structures were pre sent in the brain of ancestral tetrapods and that they were organized according to a general plan shared today by all extant tetrapods.