頭頂葉の領野区分と入出力

The parietal lobe：Architectonic areas and their connections

　頭頂葉は終脳上部の外側面から正中面にかけて存在する脳葉である。その正中面には中心傍小葉の後半部と楔前部があり，外側面前部には中心後回が，外側面後部には頭頂間溝によって上下に境された，上頭頂小葉と下頭頂小葉がある。ヒトの下頭頂小葉は，さらに縁上回と角回に区分される。中心後回の大部分は一次体性感覚野が占め，視床から体性感覚情報を受け取る。中心後回の下方や後方には二次体性感覚野や一次前庭野が存在する。一方，後頭葉皮質から頭頂葉へは視覚情報が伝えられ，視覚の背側経路をつくる。頭頂葉の連合野は，主にこれら体性感覚情報と視覚情報を統合して空間認知を行ったり，眼球運動や上肢運動の制御を行うとされる。頭頂葉後部の各領野には，その機能に応じた入出力経路が備わっており，体性感覚野，後頭葉と側頭葉の視覚関連領野，上側頭溝の多感覚連合野，帯状回や海馬傍回皮質，運動野，運動前野，補足運動野，前頭眼野，前頭前野背外側部を中心とした領野との連絡や，頭頂葉各領野間の連絡がある。

　The parietal lobe is located on the dorsal part of the cerebral hemisphere, extending from the mesial surface to the convexity. The parietal lobe is composed of the postcentral gyrus, the superior and inferior parietal lobules, the posterior half of the paracentral lobule, and the precuneus. The human inferior parietal lobule is further divided into the supramarginal gyrus and the angular gyrus.

　Those regions of the parietal lobe are further subdivided into cortical areas based on the cytoarchitecture,myeloarchitecture, chemoarchitecture, and functional properties of constituent neurons. The postcentral gyrus and the posterior half of the paracentral lobule comprise areas 3a, 3b, 1, and 2, which represent the primary somatosensory cortex（SⅠ）. The opercular portions of the postcentral gyrus and inferior parietal lobule contain the secondary somatosensory cortex（SⅡ）. The superior parietal lobule is made up of areas PE and PEc. Both areas extend onto the mesial surface of the hemisphere. Ventral to area PEc on the mesial surface, area PGm is located between the cingulate cortex anteriorly and the occipital cortex posteriorly. The inferior parietal lobule is subdivided into areas PF, PFG, and PG. The posterior end of the inferior parietal lobule and the dorsal part of the anterior bank of the lunate sulcus are covered by area DP, while the anterior bank of the parietooccipital sulcus is made up of area PO. The banks and fundus of the intraparietal sulcus are subdivided chiefly based on the functional properties of the cortex. The medial bank comprises areas PEip（5v）, MIP and PO, while the lateral bank consists of areas LIP and LOP. The deepest portion of the sulcus is subdivided into areas AIP, VIP and PIP.

　The findings so far reported on the fiber connections of each cortical area have revealed the following morphological and functional organization of the parietal cortex. The postcentral gyrus and the paracentral lobule comprises the primary somatosensory cortex, which receives somatosensory information from the posterior ventral nuclei of the thalamus. From the primary and secondary somatosensory areas, somatosensory information is transferred to the posterior parietal lobule. On the other hand, visual information concerning the space and the motion of objects reaches the posterior parietal lobe via occipital and temporal visual areas. Many of the posterior parietal areas have robust connections also with the motor, supplementary motor, and premotor cortices, the frontal eye field, and the prefrontal association cortex. The parietal lobe thus comprises the areas that（1）integrate somatosensory and visual information for spatial cognition and（2）play pivotal roles in oculomotor control and hand movements for object manipulation.