Striatal D2: Where habits and newly learned actions meet

Abstract

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. Keywords Behavior systems • Operant conditioning • HabitIt has long been proposed that learning of actions and expression of habitual behaviors are processed separately in dorsomedial (DMS) and dorsolateral striatum (DLS), respectively. Within this conceptual framework, it is further hypothesized that activity in the direct pathway could play a role in initiating actions while activation of the striatal indirect pathway might be responsible for the termination of movements. However, recent studies challenge this simple dichotomy by demonstrating that DMS and DLS coordinate with each other and that heterogeneous activities simultaneously exist in direct and indirect pathways.

Molecular Landscape of Tourette’s Disorder

“…Furthermore, these MSNs receive convergent excitatory inputs from the cortical and thalamic areas and further project to the output nuclei of the basal ganglia circuit [ 115 ]. In addition, Drd2+ MSNs have been shown to be crucial in habit formation in mice [ 116 , 117 ]. This is particularly interesting because both from a cognitive-behavioral and neuroscientific perspective, tics—the hallmark of TD—can be viewed as habits that have been formed over time and that are associated with premonitory sensations and can, at least partially, be controlled [ 118 , 119 , 120 , 121 , 122 ].…”