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A programmable system was used to provide contingent reinforcement of EEG cycles corresponding to a selected criterion in a dynamic regime. Use of automated reinforcing stimulation of emotionally positive zones of the hypothalamus led to a significant increase in the number of cycles with the characteristics specified by the dynamic regime within the dominant EEG frequency bands. This effect lasted for some time after withdrawal of reinforcing stimulation, and then died down gradually. These changes in the EEG activity structure did not occur in conditions of nonassociated hypothalamic stimulation. Pseudoreinforced background EEG cycles showed complex nonlinear dynamics with competitive interactions between processes in which the large dimensionality of the attractor was difficult to interpret because of indeterminacy in the trends of the dominant process. In contingent hypothalamic stimulation, the form of the correlation integral changed towards a predominance of a single nonlinear process determining all the activity recorded. In fact, a single dominant nonlinear process was formed, which became responsible for the entire dynamics of the system with concordance of its internal structure.