Figure 1 (taken from 2006 review). Model of brain structure of the agonistic motivational systems common to all muroid rodents. Boxes represent assemblies of brain cells that perform a particular function. Lines represent neural pathways, with facilitative pathways indicated by forked endings and inhibitory pathways indicated by filled circles. "E" and "A" represent the organizing and activating effects of estrogen and androgen hormones, respectively, while "C" and "P" represent actions of corticosteroids and hormones of preganancy and lactation, respectively. Numbers in brackets, indicate locations of learning effects.