Of particular interest is the medial PFC (mPFC), which is one of the last brain structures to develop in both humans and rats, yet its development occurs at different time points for each species. In humans, neurogenesis and migration of neocortical neurons occurs during the third trimester of fetal development, with the more superficial layers of the neocortex being formed last (Goldman-Rakic et al, 1983). Moreover, there is a rapid increase in the length of basilar dendrites of future Layer III and Layer V pyramidal neurons during the third trimester, while the number of basilar dendrites per pyramidal neuron appears to stabilize at the onset of the third trimester (Mrzljak et al., 1992). It is also during the third trimester when dendritic spines begin appearing on Layer III and V pyramidal neurons (Mrzljak et al., 1990). Other developmental processes, such as dendritic maturation and synaptogenesis, continue to occur postnatally, with the most rapid changes occurring in the first few years of life. (Goldman-Rakic et al., 1983; Anderson et al, 1995; Huttenlocher and Dabholkar, 1997). In rats, the medial prefrontal cortex
