Papez回路

機能 / Function

情動と記憶（特にエピソード記憶の形成）に関わる辺縁系の閉回路。海馬体→脳弓→乳頭体→乳頭視床路→視床前核→視床帯状放線→帯状回→帯状束→海馬傍回（嗅内皮質）→海馬体へと戻る。Papez（1937）が情動の神経回路として提唱し、現在は記憶の形成・固定化に重要とされる。

A closed limbic loop for emotion and (especially episodic) memory formation: hippocampal formation → fornix → mammillary body → mammillothalamic tract → anterior thalamic nucleus → thalamocingulate radiation → cingulate gyrus → cingulum → parahippocampal/entorhinal cortex → back to the hippocampus. Proposed by Papez (1937) for emotion; now regarded as important for memory encoding and consolidation.

主要構造 / Key structures

• 海馬体Hippocampal formation
• 脳弓Fornix
• 乳頭体Mammillary body
• 視床前核Anterior thalamic nucleus
• 帯状回Cingulate gyrus
• 海馬傍回（嗅内皮質）Parahippocampal (entorhinal) cortex

回路破綻による症状 / Symptoms of disruption

回路の障害で前向性健忘を主とする記憶障害。チアミン欠乏では急性のWernicke脳症（眼球運動障害・失調・意識障害）を経て、乳頭体・内側視床などの障害により慢性のKorsakoff症候群（前向性・逆向性健忘と作話）を残す（病変は乳頭体・視床・視床下部・中脳水道周囲灰白質に及ぶスペクトラム）。脳弓損傷（第三脳室近傍の手術・腫瘍）でも健忘。海馬・嗅内皮質の変性はアルツハイマー病の早期病変でエピソード記憶障害の責任病巣。辺縁系脳炎でも同回路が侵される。

Disruption causes memory impairment, predominantly anterograde amnesia. In thiamine deficiency, acute Wernicke encephalopathy (ophthalmoplegia, ataxia, confusion) may be followed by chronic Korsakoff syndrome (antero/retrograde amnesia and confabulation) from damage to the mammillary bodies and medial thalamus (a spectrum involving mammillary bodies, thalamus, hypothalamus and periaqueductal grey). Fornix injury (third-ventricle surgery, tumors) also causes amnesia. Hippocampal/entorhinal degeneration is the early lesion of Alzheimer's disease responsible for episodic memory loss; limbic encephalitis likewise targets this circuit.

臨床症候・疾患 / Clinical correlations

Papez 回路(海馬-脳弓-乳頭体-視床前核-帯状回)の障害で前向性健忘。Wernicke-Korsakoff 症候群(チアミン欠乏)では乳頭体・乳頭体視床路・内側視床(背内側核)を中心に障害される。アルツハイマー病(海馬・嗅内野)、辺縁系脳炎、脳弓・視床の血管障害。

Damage to the Papez circuit (hippocampus–fornix–mammillary body–anterior thalamus–cingulate) causes anterograde amnesia. Wernicke-Korsakoff syndrome (thiamine deficiency) predominantly involves the mammillary bodies, mammillothalamic tract and medial (dorsomedial) thalamus; Alzheimer's disease (hippocampus/entorhinal), limbic encephalitis, fornix/thalamic stroke.

Clinical pearl — 乳頭体・乳頭体視床路・内側視床障害(Wernicke-Korsakoff)で前向性健忘。AD は海馬・嗅内野から。

Mammillary bodies / mammillothalamic tract / medial thalamus (Wernicke-Korsakoff) → anterograde amnesia; AD begins in hippocampus/entorhinal cortex.

出典 / References

• Papez JW. Arch Neurol Psychiatry 1937
• Catani M, et al. Cortex 2013 (limbic connectivity)