The Papez circuit

The appearance of the brain in the mid-lower part, when dissected, looks like a limbo. That is why Paul McLean, the influential American physiologist and psychiatrist, preferred to call the circuit the limbic system.

James Papez worked on the anatomy of emotion and this is how he described his circuit, the Papez circuit, in 1937. This is mainly composed of the hippocampus, the thalamus and the cingulum. However, it seems that this idea had already been contemplated before Papez presented it.

So, Authors such as Paul Broca and Paul McLean added other structures to the circuit of emotion. Among them were the septum, the amygdala and the hypothalamus, forming the limbic system. On the other hand, neurologist Paul Ivan Yakovlev proposed an emotional circuit that included the orbitofrontal, anterior temporal, insular lobes, and other nuclei of the thalamus.

So, It has been seen that the Papez circuit may be related, apart from emotions, to memory and damage to its various components. in Parkinson’s disease, Alzheimer’s disease, Korsakoff syndrome, semantic dementia and global amnesia.

Who was James Papez?

The American neuroscientist James Papez (1883 – 1958) was pioneer in the study of comparative neuroanatomy. Thus, he identified a circuit in the mammalian brain that subserves emotional experience and the eponym, the Papez circuit, is firmly established in medical vocabulary.

Papez He worked in the isolated laboratory at Cornell University. Here he was practically immersed in the practice of examining slides under the microscope. This allowed him to definitively identify this circuit.

How is the Papez circuit formed?

Papez’s circuit begins from the formation of the hippocampus, known as subiculum. It then crosses the body of the mammillaries. It then traverses the mammillothalamic tract, often known as the Vicq d’Azir tract, and synapses on the anterior thalamic nucleus. From there, it reaches the cingulum, travels through the entorhinal cortex and returns to the formation of the hippocampus. and has a length of approximately 350 millimeters.

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A proposal for the mechanism of emotion

Papez published his observations in 1937 in a historical document titled “A proposal for the mechanism of emotion” in the magazine Archives of Neurology and Psychiatry. This is what Papez described:

“The central emotional process of cortical origin can be conceived as a formation in the hippocampal formation and is transmitted to the mammillary body and then to the Vicq d’Azir tract and from there through the thalamic nuclei anterior to the cortex of the cingulate gyrus. … It is evident that the proposed mechanism of emotion will have to pass the test of experiment and clinical experience to be useful in science… The hypothalamus, the anterior thalamic nucleus, the cingulate gyrus, the hippocampus and their interconnections constitute a harmonious mechanism that can elaborate the functions of the central emotion and participate in emotional expression.”

Before Papez

Like we have already said, The concept of an anatomical substrate for emotion did not begin with the works of James Papez. In 1907, the neuropathologist Christfried Jakob (1866 – 1956) alluded to the visceral brain and conceived the presence of an internal brain that presents emotional mechanisms of viscera. This scientist based his hypothesis on experiments on the degenerative brains of monkeys and dogs, as well as autopsied materials from the human brain (2).

The appearance of the brain in the mid-lower part, when dissected, looks like a limbo. That is why Paul McLean, the influential American physiologist and psychiatrist, preferred to call the circuit the limbic system. Thus, other researchers called it the Papez-McLean circuit.

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The Papez circuit and memory

Apart from the role of the Papez circuit in the field of emotion, some authors have found evidence that memory also has its roots there. They point to a strong synchronization of theta waves in the hippocampus and ventral anterior thalamus. Since these waves deal with problems such as memory and learning, several workers have suggested that the Papez circuit could be involved in mnemonic functions. Some scientists have even reduced it to the realm of spatial and episodic memory (3, 4).

It seems then that the Papez circuit is both an emotional system and a system that has to do with memory. This is a discovery that, although it had already been mentioned before, James Papez finished outlining and that was decisive for the neuroanatomy of emotion.