Figure 4. Path diagrams that represent three structural models, i.e., extraversion (A), behavioral facilitation (B), and neurobiological facilitation (C). In A and B, extraversion and facilitation are proposed to correspond in that they both are associated with a central modulatory mechanism that facilitates the general behavior pattern of approach and, subsequently, lower-order traits or specific behavior patterns, respectively. In part C of the figure, the neurobiological foundation of the facilitation mechanism is illustrated as the broadly projecting VTA dopamine neurons, which facilitate approach behavior and, subsequently, specific behavior patterns. Also in part C, the neurobiological structures that serve as regions of integration for the underlying processes illustrated in parts A, B, and C are defined. Furthermore, the existence of separable, parallel cortical networks that integrate complex cognitive processes which would guide incentive motivated behavior through the environment are indicated in part C. VTA = ventral tegmental area; VPm = ventromedial subterritory of the ventral pallidum; NASshell = shell subterritory of the nucleus accumbens, a part of the ventral striatum; BL-E Amygdala = basolateral complex and extended amygdala. See the text for details on the functional interactions among the various levels of the path diagrams.