Papez Circuit - History

History

In 1907/1908, Bavarian neuropathologist Christfried Jakob discovered the visceral brain. By date, he held the "... first interpretation of the limbic or ‘internal’ brain as a viscero-emotional mechanism..." He traced the structures of the system based on degeneration experiments in apes and dogs as well as neurodegenerative diseases in humans.

However, it was not until 1937 when James Papez studied this system in detail that it became famous. Papez had been studying cases of rabies which is a disease that causes high levels of aggression. He noticed that this heightened aggression correlated with damage to the hippocampus. Theoretically, this made sense to Papez who asserted that the hippocampus is responsible for the expression of emotion because of its connection to the autonomic nervous system. He also noticed that in other cases, certain stimuli (taste, smell, pain, etc.) would cause strong emotional responses. These stimuli activated not only the hippocampus but also other brain structures. He theorized that these brain structures worked together as the emotional control center in the brain and consequently founded the Papez circuit. Because of these studies, Papez strongly believed that the circuit was the cortical control of emotion.

Around the same time, Paul D. MacLean was also interested in the Papez circuit. He had read through Paul Broca's research which indicated that the limbic lobe that surrounds the brainstem is a structure present in all mammals. Papez's paper on the emotional circuit which involved the connection between the hypothalamus and the limbic lobe set MacLean on a journey to learn more. He visited Papez at Cornell University after which he proposed a modified version of the Papez circuit in 1952, emphasizing not only the hippocampus, but also the amygdala and septum.

The hippocampus, amygdala, and septum make up the rhinencephalon (frontotemporal portion of the brain) or, as Jakob termed it, the visceral brain. Together, the limbic lobe and the visceral brain make up the limbic system. MacLean believed that including the visceral brain in the limbic system accounted for the external sensory information associated with subjective emotional experiences. Since the limbic system consists of evolutionary primitive structures which prevents its interpretation verbally, the visceral brain accounts for the visual, auditory, olfactory, and other external sensory inputs that are associated with emotions.

Recently, many studies have been done to analyze the anatomy and function of the Papez circuit. Many scientists have been finding proof that the circuit is related to memory as well as emotion. The limbic system, the modified version of the circuit proposed by MacLean, is thought to be involved in the same functions as well as behavior, motivation, and olfaction.