アディクションの神経基盤—2つのドーパミン神経系と強化との関係

Multiple Dopamine Signals and Their Contributions to Reinforcement Learning

動物がある行動の後に報酬を得ると，その行動を繰り返すようになる。中脳のドーパミンニューロンは，このような報酬による行動の「強化」にとって重要な神経基盤であり，アディクションとの関係が注目されてきた。一方，近年の研究は，ドーパミンニューロンの中には報酬とは無関係なシグナルを伝達するものも多く存在することを報告している。本稿では，ドーパミンシグナルについての最新の知見と，その強化との関係を概説する。

Abstract

Midbrain dopamine neurons are activated by reward and sensory cue that predicts reward. Their responses resemble reward prediction error that indicates the discrepancy between obtained and expected reward values, which has been thought to play an important role as a teaching signal in reinforcement learning. Indeed, pharmacological blockade of dopamine transmission interferes with reinforcement learning. Recent studies reported, however, that not all dopamine neurons transmit the reward-related signal. They found that a subset of dopamine neurons transmits signals related to non-rewarding, salient experiences such as aversive stimulations and cognitively demanding events. How these signals contribute to animal behavior is not yet well understood. This article reviews recent findings on dopamine signals related to rewarding and non-rewarding experiences, and discusses their contributions to reinforcement learning.