Many of us have heard of Papez Circuit, the neural network that controls human emotion.

In 1937, James Papez wrote an article called A Proposed Mechanism of Emotion. He begins his article by citing the relevant word of Bard and Cannon, who will be discussed in a later article. But Papez cites the reason for his article was to discuss the hypothalamus, hippocampus, the gyrus cinguli (aka the cingulate gyrus), and their interconnections.

He says:

He further wrote:

In other words, emotional expression, as according to Bard’s experiments, depends on the hypothalamus rather than the thalamus or cortex. However, the subjective aspects of emotions depends more on the cortex, which then plays a role in understanding what we are feeling, and why.

Papez spends a significant amount of time explaining the neuroanatomy he thought was involved in emotion:

He uses the above diagram, going through the connection between parts, and what he thought that meant. For example, he says the mammillary bodies have a connection between the hypothalamus and the cortex:

Now, Papez circuit itself is a proposed network whereby it is the hypothalamus which bears the most significance to emotional expression. Interestingly, Papez work had involved cases of rabies, which can produce aggression in those afflicted with it. He found that there was damage to the hippocampus, which led Papez to believe then that it was the hippocampus which was responsible for emotional expression. He also further noted that the stimulation of the senses, such as taste or smell, could bring about emotional responses, thus giving him more reason to believe that it was the hippocampus that is responsible for the expression of emotion.

The Papez circuit involves a number of brain structures:

hippocampus → fornix → mammillary bodies → mammillothalamic tract → anterior thalamic nucleus → cingulum → entorhinal cortex → hippocampus

The hypothalamus and the cortex are connected in Papez circuit, and are seen to act as the emotional network of the brain. Papez stated that the cingulate cortex projects to the hippocampus, which then projects to the hypothalamus via the fornix. And though his anatomy may be correct, Papez interpretation of the circuit was not fully right.

Of course, we know today that the hippocampus is responsible for emotion. With Papez work on aggression, he thought it was the hippocampus that was responsible for aggression. However, we know today that the amygdala (which is close to the hippocampus) receives connections from the hippocampus. Considering the hippocampus is the storage of memories, (somewhat so, though things are more complicated than this, and will be explored in a future article), it makes sense then that certain emotions may be triggered by strong memories.