Sleep spindles (waxing and waning cycles of amplitude at 12–18 Hz) of electrical activity of the mammalian brain were modeled based on the pacemaker mechanism of the sigma rhythm. The spindles were assumed to result from the rhythmic interaction between cortical neurons and medial thalamic cells, which was simulated by a system of oscillatory units operating in the mode of small vacillations. Transition to deep slow-wave sleep is considered to result from increased density of interactions and the number of oscillatory units, and these specific rearrangements are discussed in terms of adaptation of organisms with high and low anxiety to environmental changes.

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