A hypothetical mechanism is proposed for the functioning of neural networks including limbic structures, the neocortex, and the basal ganglia. This hypothesis is based on existing data showing that the hippocampus, amygdala, and prefrontal cortex interact with each other, that the inputs of these structures converge on spiny neurons in the nucleus accumbens, and that these inputs are organized topically and can be modified. As GABAergic spiny cells in the nucleus accumbens innervate neurons in the output nucleus of the basal ganglia, which have inhibitory influences on the conduction of excitation via the thalamic nuclei to the limbic structures and neocortex, the extent of activation of neurons in these areas and, hence, the selection of behavior, is to a significant extent dependent on the types of responses mounted by spiny cells. When simultaneous fi ring of neurons in the limbic structures and cortex occurs, summation of excitation on spiny cells and increases in their responses lead ultimately to increased cortical activity and strengthening of cortical influences on the selection of behavior. When neurons in the two structures fi re with a time shift, excitation of neurons in the structure strongly activated first can undergo a further increase due to disinhibition of the thalamic nuclei via the basal ganglia, while the activity of neurons in the other structure can be suppressed, if the responses of spiny cells to the excitation arriving from this structure is decreased. This decrease can be the result of heterosynaptic depression, which is based on potentiation of the efficiency of the excitatory inputs from a number of structures converging on inhibitory interneurons in the nucleus accumbens and basolateral amygdala. As a result, the selection of behavior is determined by which structure was involved in activity first. Lesioning of different inputs in the nucleus accumbens from the limbic structures must lead to different behavioral impairments due to the topical organization of these inputs.