Striatal D2: Where habits and newly learned actions meet.

Smith et al. in Nature Communications, 12, 5121, (2021) provided evidence to challenge the simple dichotomy that learning of actions and expression of habitual behaviors are processed separately in dorsomedial (DMS) and dorsolateral striatum (DLS) by demonstrating that D2 receptor-expressing medium spiny neurons (D2-MSNs) in anterior DLS could modulate newly learned action, except for its involvement in the expression of habitual actions. Here we review recent advances and introduce a valuable addition to the traditional hypothesis by taking into account the common ligand of D1 and D2 neurons, dopamine.