In summary, we propose distinguishing fully and partially-reprogrammed iN cells based on a specific combination of molecular and functional characteristics. We suggest that the critical feature of fully reprogrammed iN cells should be the demonstration of synaptic competence as determined by the presence of spontaneous and evoked postsynaptic currents in mixed or pure neuronal cultures. iN cells can be assessed either in vitro or after transplantation into rodent brains, which may provide a better environment for maturation.
