9604799 Wessel How do biophysical neuronal mechanisms interact to achieve the computations required for proper function of neural circuits? Largely due to recent advances in optical imaging of neuronal activity we now believe that the single neuron is far more complex and dynamic than previously known from single electrode studies. A combination of electrode recording and optical imaging methods on the nervous system of he leech has been developed recently. This combination of methods will be used to investigate the integration of synaptic inputs in the dendrites of single neurons. The following specific questions will be asked: (1) What is the cellular basis of a non-linear response to sensory synaptic inputs ? (2) Do portions of a neuron act as relatively independent functional units ? The leech offers spatially extended neurons with evidence, from past work, for non- trivial processing. The established neuronal circuitry and anatomically localized connections between identifiable neurons in the leech are particularly advantageous in the study of single neuron computation. It is thus possible to stimulate one or more identified cells presynaptic to the cell under study, and monitor the dynamic interaction of postsynaptic potentials along neuronal processes. In addition, due to the small number of neurons in the leech ganglion, single neuron computation can be understood within the network context. The proposed project will extend our understanding of neuronal computation from the level of biophysical mechanisms of single neurons to the collective computation of a small neuronal network that produces behavior. Since the results focus on the properties of single nerve cells, they will likely generalize to all species, including humans.
