We hope to continue a number of complementary studies of interactions between neurons in both mammals and invertebrates. In each case we will record simultaneously but separably the activities of several neurons. With intracellular recordings and PSP shape sorting we shall be examining synaptically related assemblies of neurons; the detailed anatomy of such neurons will be studied by dye injection techniques. With extracellular recordings either from several electrodes or from a single electrode with spike-shape sorting, we shall be examining spatial assemblies of neurons. We will use computer and mathematical techniques to examine spike trains and membrane potentials in order to determine the functional organization of each observed neuronal group. Further mathematics for this purpose will be developed. By making appropriate changes in the stimulus or behavior conditions of the experiments, we will be able to determine whether the organization or boundaries of a neuronal assembly vary with time, state, or task. Experimental data will be obtained from neurons of: a. motor cortex during behavioral set states. b. sensory cortex mediating the stimulus in the same animals. c. lateral geniculate and retina during visual stimulation. d. crayfish thoracic ganglia during conditioning.