Parallel Excitatory and Inhibitory Neural Circuit Pathways Underlie Reward-Based Phasic Neural Responses

Figure 2

Model circuit. Orange arrowheads denote excitatory pathways, blue circles denote inhibitory pathways, and hemidisks denote synapses at which learning occurs. Black dashed lines denote dopaminergic signals. Evidence [21] shows that the ventral striatum (VS) excites PPTN and ventral pallidum (VP). Striosome neurons project to GPi neurons which in turn project to GPb. Dopaminergic (DA) neurons are excited by cortical inputs () encoding conditioned stimuli and lateral hypothalamus inputs encoding unconditioned stimuli via the path VS-VP-GPb-LHb-RMTg-VTA/SNc and the path VS-PPTN-VTA/SNc path. DA neurons are inhibited by via the path striosome-VTA/SNc. Note that the striosome contains an adaptive spectral timing mechanism and can learn to generate lagged, adaptively timed signals [16]. LHb neurons are excited by via the path striosome-GPi-GPb-LHb. LHb neurons are inhibited by and via the path VS-VP-GPb-LHb.