Summary of pathways linking prefrontal cortex with structures associated with perception and expression of emotions. Line thickness represents the density of projections. Direct and indirect sensory input to the orbitofrontal cortex: The orbitofrontal cortex and the amygdala receive projections from every sensory modality through the cortex (pathways so, s), and are robustly linked with each other, providing the structural basis for direct (so), and indirect (s and s') sensory input to the orbitofrontal cortex. The orbitofrontal cortex disinhibits hypothalamic autonomic centers: Orbitofrontal axons terminate heavily in the intercalated masses of the amygdala (IM, pathway a), which project to the central nucleus (a'), which projects to hypothalamic autonomic centers (pathway b). Activation of pathways (a, a') leads to disinhibition of hypothalamic autonomic centers, which innervate brainstem and spinal autonomic centers (pathways c', o'). Direct and indirect pathways from medial prefrontal areas to hypothalamic autonomic centers: The direct pathway courses from medial prefrontal cortex to hypothalamic autonomic centers (c), forming asymmetric (and presumed excitatory) synapses in the lateral and posterior hypothalamic areas. The indirect pathway courses from medial prefrontal cortices to the parvicellular sector of the basolateral nucleus of the amygdala (BLpc, pathway d), which projects to hypothalamic autonomic centers (d'), and is presumed to be excitatory. Activation of the direct or indirect pathways ultimately activates brainstem and spinal autonomic nuclei (pathways c, c', o'), which innervate peripheral organs. Red, inhibitory pathways; green, excitatory pathways.