<p>This paper examines backward conditioned connections(CC) as a universal principle of brain function. The first section presents a historical perspective on the problem: the discovery of the phenomenon of backward CC, the rules and patterns of its manifestations (the role of the ratio of the strengths of paired stimuli, the duration of the conditioned stimulus, the delay between the conditioned and unconditioned stimuli, the number of combinations, and other factors). The second section examines a number of hypotheses explaining the formation, functioning, and role of bidirectional conditioned connections in the organization of overall behavior. The final section describes the current state of the problem of backward CC:studies of second-order reflexes, sensory preconditioning, the analysis of stimulus equivalence, and the role of context. The significance of dopamine in backward CC and the role of these connections in memory reconsolidation are considered. Attention is drawn to modern neurochemical, electrophysiological, optogenetic, and other methods for studying backward CC.</p>