species is called a neuronal species. When neurons of about the same morphology is observed at the same place in another animal species, it is a neuronal genus. There are also neuronal families and so on. For example, spiny neurons of the striatum of macaque are one species. Along with that of man and/or other species they form a genus. Statistical comparisons allow to analyse what remained the same or what has changed in evolution. Starting from objectively defined neurons, it became possible to constitute neuronal sets. Neuronal sets Sets «The theory of set underlies virtually every branch of mathematics» (Kahn, 1995). Great changes in the way of analysing and reasoning have been brought by set theory . This starts from simple concepts. For instance «a set is a collection of elements » (Kahn, 1995) which is intuitive and has not to be demonstrated. The elements have in common to be members of the set. A particular set is defined by the common properties of its elements. This raises problems of similarities and finally of typology and classification. Neuronal sets Neuronal sets may be sets of entire neurons or of neuronal parts. Theoretical hodology Neuronal systems Our ability to think, react and remember relies on the function of the nervous system. We cannot understand the human brain without first elucidating the properties and function of its main unit elements, the neurons. These are complex and specialized cells. However, the improved understanding of cellular evolution achieved over the last several years has revealed that even the most sophisticated and unique properties of nerve cells represent an adaptation of basic functions observed in all eukaryotic cells, including unicellular organisms. Thus, cellular neurobiology has become an important chapter of cell biology. Studies of neurons greatly capitalize on progress in fundamental cell biology. Conversely, research on specialized features of neurons is producing major fall-outs in other areas of biology. Projects of cellular neurobiology in the department focus on mechanisms in membrane traffic at the synapse, on the development and maintenance of cell polarity and on the mechanisms responsible for the heterogeneous distribution of organelles and macromolecules within the neuronal cytoplasm. Formation and plasticity of synapses are also investigated. In the tradition of the department, questions in these fields are approached in a multidisciplinary fashion using genetics, protein and lipid biochemistry, molecular biology and state of the art light and electron microscopy imaging techniques. Experimental