# Papez Circuit > Papez circuit for MBBS Anatomy: hippocampus, fornix, mammillary body, mammillothalamic tract, anterior thalamic nucleus and cingulate pathway in memory. - Canonical URL: https://prepelephant.com/topics/mbbs/anatomy/papez-circuit - Exam / course: MBBS · Subject: Anatomy - Publisher: PrepElephant (https://prepelephant.com) — Prepared and reviewed by the PrepElephant Academic Review Team - First published: 2026-10-02 - Last updated: 2026-10-02 - How to cite: "Papez Circuit", PrepElephant, https://prepelephant.com/topics/mbbs/anatomy/papez-circuit ## Direct answer James Papez described, in 1937, a closed ring of structures linking the hippocampus to itself: hippocampus to fornix to mammillary body, mammillary body by the mammillothalamic tract of Vicq d'Azyr to the anterior thalamic nucleus, thalamus to the cingulate gyrus, and cingulum around to the parahippocampal (entorhinal) cortex, which feeds the hippocampus through the perforant pathway. He proposed the ring as the anatomical substrate of emotion; modern physiology assigns its stations a central role in declarative memory encoding and retrieval. Because the loop passes through six anatomically separate stations, six different diseases — from Korsakoff psychosis to Alzheimer disease — interrupt the same traffic, which is what makes this circuit an examiner's gift. ## What you must remember - **The sequence in full:** hippocampal formation → fornix → mammillary body → mammillothalamic tract (Vicq d'Azyr) → anterior thalamic nucleus → cingulate gyrus → cingulum → entorhinal (parahippocampal) cortex → perforant path → hippocampus. - **Fornix anatomy:** fimbria, crura, body and columns; the columns arch down in front of the interventricular foramen, around the anterior commissure, to reach the mammillary bodies — remember precommissural and postcommissural fibres. - **The one named tract:** mammillary body to anterior thalamic nucleus is the mammillothalamic tract of Vicq d'Azyr; the mammillotegmental tract is its less famous collateral to the midbrain tegmentum. - **Korsakoff psychosis:** thiamine deficiency in alcoholism destroys the mammillary bodies (with the dorsomedial thalamus) — anterograde amnesia with confabulation; treat suspected Wernicke encephalopathy with parenteral thiamine before glucose. - **Alzheimer disease:** neurofibrillary degeneration begins in the entorhinal cortex and hippocampus (Braak stages I-II), so recent memory is the first casualty years before cortical features. - **Herpes simplex encephalitis:** has a predilection for the temporal lobe hippocampal region — fever, behavioural change, seizures and memory loss; the circuit's entry station is destroyed. - **Surgical interruptions:** anterior communicating artery aneurysm surgery or colloid cyst removal can injure the fornix — a recognised cause of amnesia; cingulectomy historically targeted intractable pain and psychiatric disease. - **Functional tag:** emotion was Papez's original claim, memory is the modern one — a correct viva answer mentions both. ## Localising the break in the loop Four patients, four stations. The chronic alcoholic with Korsakoff psychosis has mammillary body destruction — the loop is cut at its first relay, and although the hippocampus encodes, nothing reaches the anterior thalamus for consolidation and retrieval. The patient after anterior thalamic infarction (a paramedian thalamoperforating artery occlusion) has the same amnesia with intact mammillary bodies — the same traffic, blocked one station later. The elderly man whose Alzheimer disease begins in the entorhinal cortex loses the input gateway: the hippocampus is isolated from cortical information, so nothing new is encoded at all. And the young woman after colloid cyst excision with fornix injury shows that even the cable matters — unilateral fornix damage is often tolerable, bilateral damage is devastating. The unifying bedside lesson is that anterograde amnesia can be produced by a lesion at any station from entorhinal cortex through fornix, mammillary body and anterior thalamus — a differential that examiners phrase as "give four structural causes of recent memory loss". ## Where students slip Two slips dominate. Students run the loop backwards after the mammillary body, sending fibres directly to the cingulum — the anterior thalamic nucleus and its thalamocortical projection must be named in between. And they conflate fornix with cingulum: the fornix is the arched cable under the corpus callosum carrying hippocampal output forward; the cingulum is the longitudinal bundle inside the cingulate gyrus carrying traffic backward to the parahippocampal region. A prof viva classic is "name the tract connecting the mammillary body to the thalamus" — Vicq d'Azyr — and "who described this circuit and for what purpose" — Papez, 1937, for emotion. ## Frequently asked questions ### Which tract connects the hippocampus to the mammillary body? The fornix, via its fimbria, crura, body and columns. The columns descend in front of the interventricular foramen of Monro to reach the mammillary bodies. ### What is the mammillothalamic tract of Vicq d'Azyr? The fibre bundle from the mammillary body to the anterior thalamic nucleus, the second link of the Papez circuit. Destruction contributes to the amnesia of Korsakoff psychosis. ### Which vitamin deficiency interrupts the circuit in alcoholics? Thiamine (vitamin B1), damaging mammillary bodies and dorsomedial thalamus — Wernicke encephalopathy progressing to Korsakoff psychosis. Give parenteral thiamine before any glucose-containing fluid. ### Which station degenerates first in Alzheimer disease? The entorhinal cortex and hippocampus, in Braak stages I-II. Recent memory therefore fails years before language and visuosocial functions. ### Why did Papez originally propose the circuit? As an anatomical theory of emotion in 1937, before the limbic system concept was formalised by MacLean. It is now regarded as central to memory processing as well.