Figure 2.

Neural architecture of explicit, rule-based category learning. Solid lines indicate excitatory input; dashed lines indicate inhibitory input. Generation of rules depends upon dopamine (DA) activity within the ventral cortico-striatal circuit, including nucleus accumbens (NAc), orbitofrontal cortex (OFC), and anterior cingulate cortex (ACC). Active maintenance of the rule in use depends upon recurrent excitation of the fronto-thalamic loop that represents that rule. Positive feedback supports rule maintenance through a phasic DA bursts to caudate, which increases excitation of the “Go” pathway and inhibition of the “NoGo” pathway and enables disinhibition of the relevant fronto-thalamic loop. Negative feedback triggers a phasic dip in DA availability in caudate, resulting in enhanced inhibitory output from GPi. This destabilizes the relevant rule representation in WM and increases the likelihood of a shift. Release of norepinephrine from the locus ceruleus may also govern shifting activity. Selection of the new rule depends upon the relative pattern of activation within ACC, which biases the relative patterns of activation of rule representations in prefrontal cortex (PFC). Unexpected negative or positive feedback triggers a phasic dip or burst, respectively, in DA release from the ventral tegmental area. These phasic changes alter activation in NA and ACC and these error-driven changes in ACC activation regulate activation of relevant rule representations in PFC.