The fourth Intensive Study Program (ISP) of MIT's Neurosciences Research Program was held in the summer of 1977. Previous volumes developed from ISPs have formed focal points in the evolution of the field of neuroscience, and the present volume continues this tradition of excellence. It differs from its predecessors, however, in that the entire ISP was based on the exploration of a single concept: local circuit interaction, structural (cellular), electrical, and chemical. From the beginning of modern brain research, emphasis has been put on long-range interactions, because the long-tract axons that carry relatively long-distance messages and the synapses they make upon dendrites and neuronal cell bodies have been relatively accessible to study. Recently attention has been focused on the important role of neuronal local circuits, emphasizing dendrites and dendrodendritic synaptic interaction between neurons whose axons may be short or completely absent. The most interesting brain activities—those thought to be concerned with higher functions—occur in the neuropil where myriad axons synapse on fine dendrites of intrinsic neurons of the cortex, and it is here that local circuitry is found. The emphasis on local circuitry does not mean that the ISP was narrower in overall scope than previous ISPs. Chemical, physiological, and anatomical aspects of the subject were all discussed. An entire day was devoted to the retina, because this neural tissue offers a good example of purely local circuit interactions. Models of neuronal networks were introduced, as were detailed models of the cell surface and of stages leading to the growth and interaction of neurons. And at the end a hypothesis was advanced to show how all of this might apply to higher brain functions (learning, memory, perception, awareness, consciousness). The Neurosciences: Fourth Study Program consists of 68 chapters divided into the following sections: Keynote Papers; Introduction to Local Circuits; Elements of Retinal Function; Spikeless and Electronic Information Processing; Structural Aspects of Local Circuits; General Principles of Neuronal Integration; High-Sensitivity Transduction; Membrane Dynamics and Cellular Interaction; Chemical Regulation and Transduction; Phosphorylation and Ion Transport; Regulation of Gene Expression in the Nervous System; Modulators and Effectors of Neuronal Interaction; and A Theory of Higher Brain Function.