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 :

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

Pathway

Information from cortical association areas passes to the hippocampus via the cingulate gyrus, cingulum and parahippocampal gyrus. After information processing in the hippocampus, signals are transferred to the hypothalamus (mammillary body) via the fornix. Completion of the circuit and feedback to the cortex is accomplished through mammillothalamic 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 :

Hippocampus → fornix → mammillary body → mammillothalamic fibers→ thalamus (anterior nucleus) → cingulum→ entorhinal cortex → hippocampal formation.

Radiographic features

MRI and DTI (diffusion tensor imaging)

The pathway described above can be imaged using MRI and diffusion tensor imaging (DTI) in particular.

History and etymology

In 1930, James Papez suggested that the cognitive activity in the cortex affects the expression of emotions through connections 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 .