The vocal control nucleus, HVc, of the songbird forebrain undergoes neurogenesis in adulthood, as ventricular zone precursor cells divide and their daughter cells migrate into the subjacent forebrain, where they differentiate into neurons. We have previously demonstrated that the migration and development of these new neurons can proceed in vitro, in HVc ventricular zone explant cultures derived from the adult canary HVc. By a combination of electron microscopy and electrophysiology, we now report that these newly produced neurons become functionally mature and synaptically competent in culture. These cells developed synaptic contacts which became morphologically evident during the second week in culture, and which preceded the development of both stimulus-evoked and spontaneous action potentials during the second and third weeks in vitro. Thus, the newly generated neurons of the adult avian forebrain can form structurally complex, electrically interactive networks in long-term culture.