大脳皮質-線条体の神経回路

Neuronal Linkage of the Cerebral Cortex and the Striatum

はじめに

　われわれは行動するとき，達成すべき行動目標を正しく設定するため，視覚，聴覚，体性感覚など，外界からの感覚情報や，学習，記憶，情動など，自己が持つ内部情報に基づいて行動計画を立案し，実行する。行動の発現と制御には，これらの情報やこれらの情報から生成される認知情報を扱う大脳皮質と，大脳皮質のほぼ全域から入力を受ける大脳基底核が重要な役割を担っている。線条体は大脳基底核の入力核であり，運動，感覚，認知，情動など，大脳皮質に由来するさまざまなタイプの情報が入力する。

　本稿では，このような皮質線条体入力をはじめ，大脳皮質と線条体をつなぐ神経ネットワークについて概説する。

Abstract

　The striatum is the major input station of the basal ganglia. It receives a wide variety of inputs from all areas of the cerebral cortex. In particular, there are several parallel loop circuits, such as the motor, oculomotor, dorsolateral prefrontal, lateral orbitofrontal, and anterior cingulate loops, linking the frontal lobe and the basal ganglia. With respect to the motor loop, the motor-related areas, including the primary motor cortex, supplementary motor area, dorsal and ventral premotor cortices, presupplementary motor area, and rostral and caudal cingulate motor areas, send inputs to sectors of the putamen in combination via separate (parallel) and overlapping (convergent) pathways. Such signals return to the cortical areas of origin via the globus pallidus/substantia nigra and then the thalamus. The somatotopical representation is maintained in each structure that constitutes the motor loop. Employing retrograde transsynaptic transport of rabies virus, we have recently investigated the arrangement of multisynaptic pathways linking the basal ganglia to the caudal aspect of the dorsal premotor cortex (the so-called F2). F2r, the rostral sector of F2, has been shown to be involved in motor planning, whereas F2c, the caudal sector of F2, has been shown to be involved in motor execution. We analyzed the origins of multisynaptic inputs to F2r and F2c in the basal ganglia. Our results indicate that the 2 loop circuits connecting the F2r and F2c with the basal ganglia may possess a common convergent window at the input stage, while they have parallel divergent channels at the output stage.