Butler IBN-9728155 In mammals, the neocortex which receives diverse sensory inputs and include sites of higher cognitive functions, forms from the telencephalic pallium. The highly laminar, or layered, arrangement of the neurons in neocortex is an exception to the way in which this brain area develops in most of the major radiations of vertebrates. Among the latter, elaboration and expansion of the telencephalic pallium has occurred independently over evolution and is characterized by the presence of various nuclear groups, i.e., the neurons are arranged in a nonlaminar manner. One current hypothesis (proposed by Karten) is that these nuclei in the elaborated pallia of nonmammals represent equivalent cell populations to the cell populations that form the respective laminae in mammalian neocortex. A large body of data on neuronal connections and histochemistry supports this hypothesis for the nuclear pallial groups present in birds. This proposal seeks to determine--by the study of the connections of pallial regions with anatomical tracing techniques--whether the "equivalent cell hypothesis" can be extended to aminote vertebrates, i.e., whether similar nuclear groups with similar connections can be identified in systems with elaborated telencephali pallia. Specifically, it is predicted that in very simple unelaborated pallia, only one cell population dedicated to the visual system is present. Whereas in elaborated and expanded pallia, two or more separate cell populations dedicated to visual processing are present. Such a result would support Karten's equivalent cell hypothesis. Further, this result would support the hypothesis that such multiple cell groups evolved by the process of parcellation (as proposed by Ebbesson), which states that a single cell group can divide over evolution into two or more daughter cell groups with parceled connections and functions.
