Papez circuit

The Papez circuit is a fundamental component of the limbic system. It is a closed neural circuitry that starts and ends in the hippocampus. It is also known as the medial limbic circuit.

Gross anatomy

The Papez circuit involves different structures of the brain including ²:

• hippocampus and adjacent cortex (entorhinal cortex)
• fornix
• mammillary bodies
• anterior nucleus of the thalamus
• cingulum

 Pathway

Information from cortical association areas passed to the hippocampus via cingulate gyrus, cingulum and parahippocampal gyrus. Following information processing in the hippocamps, signals are transferred to the hypothalamus (mammillary body) via the fornix. Completion of the circuit and feedback to the cortex accomplished through mamillothalmic fibers, relaying information from the hypothalamus to the anterior nucleus of the thalamus. The anterior nucleus of the thalamus projects fibers to the cingulate gyrus, cingulum and parahippocampal gyrus back to the hippocampus.

In a more succinct format:

Hippocamus → fornix →mammillary body → mammilothalamic fibers→ thalamus ( anterior nucleus ) → cingulum→ entorhinal cortex → hippocampal formation ². 

Radiographic features

MRI & DTIand DTI(diffusion tensor imaging)

Fibers from the hippocampus form the alveus, then the fibers coalesce to form the fimbria. The fimbrial fibers form the fornix, which project to the mammillary bodies via the post-commissural fornix. The mammillary bodies project primarily to the anterior thalamic nucleus (mammillothalamic tracts). The anterior thalamic nucleus in turn projects to the cingulum deep to the cingulate gyrus to reach the temporal lobe (entorhinal cortex), where the fibers project back to hippocampus.

History and etymology

In 1930, James Papez suggested that the cognitive activity in the cortex affects the expression of emotions through connection to the hypothalamus and hippocampus. In Papez’s proposal, the hypothalamus regulates the autonomic nervous system activity during the expressions of emotions. Subsequently Paul MacLean modified Papez’s proposal to include the basal forebrain, amygdala and prefrontal cortex, and named it the limbic system. Recent studies show that Papez circuit has a more significant role in memory functions than in emotions ^1-2.