Neurons in the central nervous system of mammals and many other species receive most of their synaptic inputs in their dendritic branches and spines, but the precise manner in which this information is processed in the dendrites is not understood. In order to gain insight into these mechanisms, simulations of interactions between distal dendritic spines with an excitable membrane have been carried out, using an electrical circuit analysis program for the compartmental representation of a dendrite and several spines. Interactions between responses to single and paired excitatory and inhibitory synaptic inputs have been analyzed. Basic logic operations, including AND gates, OR gates and AND-NOT gates, arise from these interactions. The results suggest the computational power and precision of excitable spines in distal branches of neuronal dendrites, especially those of pyramidal neurons in the cerebral cortex. The applicability to information processing in distal dendrites is discussed. © 1987.