Figure 3.
Specific innate behaviors are controlled by distinct regions of the limbic system. (A) Sexual behaviors include activation of the vomeronasal organ (VNO), accessory olfactory bulb (AOB), and medial amygdala (MeA). Signal transduction from sensation to physical motivation is not always linear; once signal has reached the MeA, it is dispersed to a few areas: bed nucleus of stria terminalis (BNST), medial preoptic nucleus (mPN), and premammillary nucleus (PMN). The BNST will shunt signal from the MeA to the mPN. The mPN can activate appetitive behaviors (sniffing and pursuit) through innervation of the nucleus accumbens (NuAc) and ventral tegmental area (VTA). Additionally, the mPN passes information to the ventrolateral portion of the ventral medial hypothalamus (VMHvl), which in turn can initiate consummative behaviors through the periaqueductal gray (PAG) and spinal cord. Consummative behaviors such as mounting, intromission, and ejaculation can also be influenced by PMN inputs on the PAG and spinal cord. (B) Defensive behaviors trigger slightly different areas of the amygdala and hypothalamus depending if the stimulus is a predator or an animal of the same species (conspecific). Defense in response to a predator initiated in the AOB sends signals to the posterioventral MeA (MeApv), then to the dorsomedial portion of the ventral medial hypothalamus (VMHdm). The VMHdm will then cross-talks with the anterior hypothalamus (AH), an instance of bidirectional communication. The VMHdm, then signals to the ventrolateral portion of the dorsal PMN (PMNd), which then signals to the dorsolateral and dorsomedial PAG. Defense responses to a conspecific are initiated in the AOB which sends afferents directly to the anterior dorsal and posterior dorsal MeA (MeApd). The MeApd acts as a hub dispersing signal to three areas: mPN, VMHvl, and dorsomedial portion of the PMNd. The VMHvl will engage in cross-talk with the PMNd, which ultimately communicates with the dorsomedial and lateral PAG. (C) Maternal behavior circuit may begin in the AOB, which sends signal to the MeA. The MeA will send information to the mPN either directly or through the BNST. Pup avoidance is suppressed in the MeA and AH to initiate pup approach. Appetitive behaviors such as pup retrieval occur through activation of the VTA by the mPN. Consummative behaviors such as nursing are executed via activation of the PAG and spinal cord by the mPN.