大脳基底核回路の形態学的知見

Morphological Re-evaluation of the Basal Ganglia Network

大脳基底核は運動の実行や調節に関わっていることが知られているが，黒質-線条体のドパミン系を中心に報酬系や強化学習などの新たな機能的側面も注目されている。しかしこの領域には，直接路・間接路投射系，およびストリオソーム・マトリックス構造という2つの概念が共存しており，ネットワークの明確な理解を現在もなお困難にしている。ここでは，新しい知見も踏まえ大脳基底核の構造を解説する。

Abstract

Electrophysiological studies in monkeys have shown that dopaminergic neurons respond to the reward prediction error. In addition, striatal neurons alter their responsiveness to cortical or thalamic inputs in response to dopamine signals, via dopamine-regulated synaptic plasticity. These findings have led to the hypothesis that the striatum exhibits synaptic plasticity under the influence of reward prediction error and conducts reinforcement learning throughout the basal ganglia circuits. The reinforcement learning model is useful; however, the mechanism by which such a process emerges in the basal ganglia needs to be anatomically explained. The actor-critic model has been previously proposed and extended by the existence of role sharing within the striatum, with particular focus on the striosome and matrix compartments. However, this hypothesis has been difficult to confirm morphologically, partly because of the complex structure of the striosome and matrix compartments. Here, we review recent morphological studies that elucidate the input/output organization of the striatal compartments.