主要連合線維

機能 / Function

同一半球内の皮質領域どうしを連絡する白質線維束。上縦束/弓状束（前頭-側頭頭頂、言語の背側経路）、鈎状束（前頭眼窩-側頭極、意味・情動）、下縦束（後頭-側頭、視覚-辺縁）、下前頭後頭束（前頭-後頭、意味の腹側経路）、帯状束（帯状回に沿う辺縁連絡）などからなり、領域間統合により高次脳機能を支える。各線維束は双方向性で、図中の流れ向きは模式的なもの。

Intrahemispheric white-matter bundles connecting cortical areas: the superior longitudinal/arcuate fasciculus (fronto-temporoparietal, dorsal language stream), uncinate fasciculus (orbitofrontal–temporal pole), inferior longitudinal fasciculus (occipito-temporal), inferior fronto-occipital fasciculus (fronto-occipital, ventral semantic stream) and cingulum (limbic association). They integrate information across regions. Bundles are bidirectional; the depicted flow direction is schematic.

主要構造 / Key structures

• 下前頭回（ブローカ野）Inferior frontal gyrus (Broca)
• 上側頭回後部（ウェルニッケ野）Posterior superior temporal (Wernicke)
• 前頭眼窩皮質Orbitofrontal cortex
• 側頭極Temporal pole
• 後頭葉外側Lateral occipital cortex
• 下前頭・眼窩前頭Inferior/orbital frontal
• 前部帯状回Anterior cingulate
• 後部帯状回・楔前部Posterior cingulate / precuneus
• 海馬傍回Parahippocampal cortex

回路破綻による症状 / Symptoms of disruption

離断症候群を生じる。優位半球（通常左）の弓状束/上縦束の障害で伝導失語（流暢性と理解は比較的保たれる一方、復唱障害・音韻性錯語・自己修正が目立つ）。鈎状束は意味記憶・呼称や社会的情動行動、帯状束は記憶・注意・意欲（障害で無為=アパシー）に関与。びまん性軸索損傷・白質脳症・脱髄（多発性硬化症）・脳腫瘍やその摘出で連合線維が離断され、領域間結合の破綻による高次脳機能障害をきたす。

Lesions cause disconnection syndromes. Damage to the dominant-hemisphere (usually left) arcuate/SLF causes conduction aphasia — relatively preserved fluency and comprehension but impaired repetition with phonemic paraphasias and self-correction. The uncinate is implicated in semantic memory/naming and socio-emotional behavior; the cingulum in memory, attention and motivation (apathy when damaged). Diffuse axonal injury, leukoencephalopathy, demyelination (MS), tumors and their resection disconnect these tracts, producing higher-order deficits.

臨床症候・疾患 / Clinical correlations

弓状束(上縦束の一部)の障害で伝導失語(復唱の選択的障害、流暢で理解良好だが錯語)。鈎状束・下前頭後頭束の障害で意味処理・呼称の障害。離断症候群(脳梁離断など)。

Arcuate-fasciculus (part of the superior longitudinal fasciculus) damage causes conduction aphasia (selective repetition deficit; fluent speech with good comprehension but paraphasias). Uncinate/inferior fronto-occipital fasciculus lesions impair semantic processing and naming; disconnection syndromes (e.g., callosal).

Clinical pearl — 弓状束(SLF)障害=伝導失語(復唱障害・流暢・理解良好)。

Arcuate fasciculus (SLF) lesion = conduction aphasia (impaired repetition, fluent, comprehension preserved).

出典 / References

• Catani M, Thiebaut de Schotten M. Cortex 2008
• Schmahmann JD, Pandya DN. Fiber Pathways of the Brain, 2006