Neurons comprising nigrostriatal system play important roles in action selection.
However, it remains unclear how this system integrates recent outcome information
with current action (movement) and outcome (reward or no reward) information to
achieve appropriate subsequent action. We examined how neuronal activity of
substantia nigra pars compacta (SNc) and dorsal striatum reflects the level of reward
expectation from recent outcomes in rats performing a reward-based choice task.
Movement-related activity of direct and indirect pathway striatal projection neurons
(dSPNs and iSPNs, respectively) were enhanced by reward expectation, similarly to
the SNc dopaminergic neurons, in both medial and lateral nigrostriatal projections.
Given the classical basal ganglia model wherein dopamine stimulates dSPNs and
suppresses iSPNs through distinct dopamine receptors, dopamine might not be the
primary driver of iSPN activity increasing following higher reward expectation. In
contrast, outcome-related activity was affected by reward expectation in line with the
classical model and reinforcement learning theory, suggesting purposive effects of
reward expectation.

JOURNAL：Communications Biology

TITLE：Reward expectation enhances action-related activity of nigral dopaminergic and two striatal output pathways

DOI：https://doi.org/10.1038/s42003-023-05288-x