FGF8, FGF17 and FGF18 are expressed in the anterior telencephalon (Figure 2), and evidence suggests that this high rostral and low caudal gradient of FGF signaling contributes to prefrontal cortex (PFC) development (Fukuchi-Shimogori and Grove, 2001; Cholfin and Rubenstein, 2007). A given amount of FGFs in the developing cortical field can determine whether stem cells will form specific sub-regions such as somatosensory cortex or PFC (Fukuchi-Shimogori and Grove, 2001). Alterations in the level of FGFs have been shown to lead to abnormal behaviors in animals (Scearce-Levie et al., 2008). FGF8 is negatively regulated by BMP (Crossley et al., 2001; Ohkubo et al., 2002) and in turn, FGF8 restricts WNT3a expression, confining it into the hem region (Shimogori et al., 2004). WNT3a expression in posterior hem regions is important for the formation of the hippocampus (Lee et al., 2000).