Proper brain function depends on correct formation of neuronal circuits during development, which is well-known to exhibit temporal and spatial precision. During embryonic cortical development, different neuronal subtypes are generated from neural progenitors in a temporally defined and highly predictable manner (Okano and Temple, 2009). Spatially, many neurons migrate over a long distance to their final locations and project axons to specific regions following guidance cues (Tessier-Lavigne and Goodman, 1996). While the importance of spatial precision in neuronal development is well appreciated, the significance of strict temporal regulation is less understood. In the hippocampus, dentate granule neurons are generated continuously from neural stem cells throughout life and appear to exhibit similar morphological, histological, and physiological properties upon maturation, regardless of whether they are born during embryonic, early postnatal, or adult neurogenesis (Ming and Song, 2011). One major difference is that neurons born in the adult brain take a significantly longer time to develop (Overstreet-Wadiche et al., 2006; Zhao et al., 2006). Interestingly, neuronal activity, such as seizures, accelerates development of adult-born neurons (Ma et al., 2009; Overstreet-Wadiche et al., 2006)
