Some introductory notes on the organization of the forebrain in tetrapods

As an introduction to the main theme of this conference an overview of the organization of the tetrapod forebrain is presented with emphasis on the te lencephalic representation of sensory and motor functions. In all classes o f tetrapods, olfactory, visual, octavolateral, somatosensory and gustatory information reaches the telencephalon. Major differences exist in the telen cephalic targets of sensory information between amphibians and amniotes. In amphibians, three targets are found: the lateral pallium for olfactory inp ut, the medial pallium for visual and multisensory input, and the lateral s ubpallium for visual, octavolateral and somatosensory information. The fore brains of reptiles and mammals are similar in that the dorsal surface of th eir cerebral hemisphere is formed by a pallium with three major segments: ( a) an olfactory, lateral cortex; (b) a 'limbic' cortex that forms the dorso medial wall of the hemisphere, and (c) an intermediate cortex that is compo sed entirely of isocortex in mammals, but in reptiles (and birds) consists of at least part of the dorsal cortex (in birds the Wulst) and a large intr aventricular protrusion, i.e. the dorsal ventricular ridge. In birds, the e ntire lateral wall of the hemisphere is involved in this expansion. The int ermediate pallial segment receives sensory projections from the thalamus an d contains modality-specific sensory areas in reptiles, birds and mammals. The most important differences between the intermediate pallial segment of amniotes concern motor systems.