Neurons born in adulthood must develop in a far different environment from those born in young animals, particularly because the adult-born neurons must find their way through and integrate into functioning neural circuits. In this issue (pages 507–518), Pierre-Marie Lledo and colleagues report that the electrophysiological properties of adult-born neurons develop in a sequence different from that seen in young animals. New adult neurons born in the subventricular zone of the lateral ventricles migrate through mature neural tissue—first tangentially to the olfactory bulb and then radially to their final position. The authors used a replication-defective retrovirus expressing enhanced green fluorescent protein to identify these newborn cells in living brain tissue. Patch-clamp recordings showed that tangentially migrating neurons expressed extrasynaptic GABAA and AMPA receptors. NMDA receptors appeared later, in radially migrating neurons (shown in photo), in contrast to young tissue where NMDA receptors precede AMPA receptors. Spontaneous synaptic activity emerged soon after migration was completed. However, spiking activity did not occur until neurons were almost fully mature. This delayed maturation of excitability may serve to prevent the newborn cells from disrupting the function of circuitry already in place in the adult.