International Encyclopedia of Systems and Cybernetics

A. Harry KLOPF describes as follows his concept of the "elementary heterostat": (a neuron, an individual in a Society, and, generally an active component in a complex system, that may itself be considered a homeostat): "An elementary heterostat derives its power from the special way in which it utilizes feedback information. In the case of positive feedback (for example, excitation delivered to a neuron), not only does the input enhance the output but also the input enhances the effectiveness of recently active positive feedback loops. In the case of negative feedback (for example inhibition delivered to a neuron), not only does the input diminish the output but also the input enhances the effectiveness of recently active inhibitory feedback loops.

In this way, the heterostat not only accomplishes short-term modifications in its behavior but it also accomplishes long-term modifications, thus encoding causal relations and providing a basis for intelligence" (1972, p.61-62).