Triune brain

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The triune brain is a model proposed by Paul D. MacLean to explain the function of traces of evolution existing in the structure of the human brain. The triune brain consists of the R-complex, the limbic system, and the neocortex.

The R-complex, comprising the brain stem and cerebellum, is similar to the reptilian brain in that it controls basic, instinctive survival behavior and thinking. The limbic system, which he first introduced in a paper in 1952, is similar to the brain of lower mammals and is the source of emotions, some aspects of personal identity, and some memory functions. The limbic system comprises the amygdala, the hypothalamus, and the hippocampus. The neocortex, also known as the cerebral cortex, is similar to the brain of higher mammals and controls higher-order thinking skills, reason and speech.

MacLean's research argues that most human behavior is the result of cooperation between the three systems of the brain. However, as the hypothesis conceives the brain as a system consisting of three subsystems, all of which originated from separate points of evolutionary history, the systems are therefore not in a state of perfect equilibrium, since they actually are three relatively independent systems constituting a bigger one.