Neuropsychiatric disorders are due to disordered functioning of neurons and, in particular, their synapses (Charney et al. 2004; Graham et al. 2002; Waxman 2005). Many neuropsychiatric disorders arise from aberrations in neurodevelopmental mechanisms. In the initial stages of brain development, cell–cell interactions are the dominant force in the assembly of the brain (Wichterle et al. 2002). As circuits form, individual neurons and connections are pruned on an activity-dependent basis, driven by intrinsic activity and competition for trophic factors. Neurogenesis does not stop with maturation but in fact continues in some brain regions and appears to be required for mood regulation (Santarelli et al. 2003; Warner-Schmidt and Duman 2006). With further maturation, experience becomes the dominant force in shaping neuronal connections and regulating their efficacy. In the mature brain, these neurodevelopmental mechanisms are harnessed in muted form and mediate most plastic processes (Black 1995; Kandel and O'Dell 1992). Neuropsychiatric disorders arising from problems in early brain development are more likely to be intrinsically or genetically based, whereas those arising during later stages are more likely to be experience-based (Toga and Thompson 2005). In senescence, neurodegenerative processes may unravel neural circuits by aberrantly engaging neurodevelopmental mechanisms (Luo and O'Leary 2005).