Considerations upon the anatomical model of reward-based learning in the basal ganglia

The nigrostriatal pathway appears to be very important in the reward-based learning. The dopaminergic neurons in the substantia nigra pars compacta (SNC) fire in relation to primary rewards and reward-conditioned stimuli, but not to rewards that are expected. It has been hypothesized that the anatomical framework for the selective response of these neurons is organized in the projections from some paralimbic areas in the frontal lobe to the striosomes of the caudate nucleus, which are also directly connected with the dopaminergic neurons of the SNC. Here, we present two additional pathways that may be related with this neurophysiological finding. We hypothesize that the connections of the paralimbic cortices with the ventral system of the basal ganglia and then with the thalamus and the hypothalamus, and the circuit ventral striatum-substantia nigra pars reticulata-thalamus-striatum could be also involved in the reward-based learning.