MODEL RELEASED: Neuronal research. A biologist working with an optical microscope to study the electrical response of individual neurons. By using a micro- manipulator stage (right) the researcher may place electrodes on single neuron cells. This allows the response of a cell to be measured to an applied electric signal. A representative plot of stimulus and response may be seen in the background. The purpose of this work is to understand the mechanisms of neuronal excitability and of neuron degeneration.