Papez circuit

Papez Circuit

The Papez circuit of the brain is one of the major pathways of the limbic system and is chiefly involved in the cortical control of emotion. The Papez circuit plays a role in storing memory.

Described by James Papez in 1937, Papez discovered the circuit after injecting rabies virus into a cat's hippocampus and monitoring its progression through the brain. The initial pathway was described as follows:

• Hippocampal formation (Subiculum) → fornix → mammillary bodies
• Mammillary bodies → mammillothalamic tract → anterior thalamic nucleus
• Anterior thalamic nucleus → genu of the internal capsule → cingulate gyrus
• Cingulate gyrus → cingulum → parahippocampal gyrus
• Parahippocampal gyrus → entorhinal cortex → perforant pathway → hippocampus.

Since then, new findings in neuroanatomy and brain function by Paul D. MacLean and others have elucidated a larger circuit that also includes the prefrontal cortex (PFC), amygdala, and septum among other areas. The PFC and amygdala are key components in this larger loop.

According to “Neuroscience: Exploring the Brain”:

“Reflecting on the earlier work of Cannon, Bard, and others, American neurologist James Papez proposed that there is an ‘emotion system,’ lying on the medial wall of the brain, that links the cortex with the hypothalamus…Papez believed that the experience of emotion was determined by activity in the cingulate cortex and, less directly, other cortical areas. Emotional expression was thought to be governed by the hypothalamus. The cingulate cortex projects to the hippocampus, and the hippocampus projects to the hypothalamus by way of the bundle of axons called the fornix. Hypothalamic effects reach the cortex via a relay in the anterior thalamic nuclei.”