p524fig14.04 (a) Model basal ganglia circuit for the control of dopaminergic Now Print signals from the substantia nigra pars compacta, or SNc, in response to unexpected rewards.  Cortical inputs (Ii), activated by conditioned stimuli, learn to excite the SNc via a multi-stage pathway from the vantral striatum (S) to the ventral pallidum and then on to the PPTN (P) and the SNc (D).  The inputs Ii excite the ventral striatum via adaptive weights WIS, and the ventral striatum excites the SNc with strength W_PD.  The striosomes, which contain an adaptive spectral timing mechanism [xij, Gij, Yij, Zij], learn to generate adaptively timed signals that inhibit reward-related activation of the SNc.  Primary reward signals (I_R) from the lateral hypothalamus both excite the PPTN directly (with strength W_RP) and act as training signals to the ventral striatum S (with strength W_RS) that trains the weights W_IS.  Arrowheads denote excitatory pathways, circles denote inhibitory pathways, and hemidiscs denote synapses at which learning occurs.  Thick pathways denote dopaminergic signals.<BR>||