Specifically, the NeuN–/GFAP– cells might represent a population of NeuroD1-infected astrocytes that had lost GFAP signal but not yet acquired NeuN signal yet; whereas the NeuN+/GFAP+ cells after NeuroD1 infection might represent a population of newly converted neurons that did not lose GFAP signal yet but already acquired NeuN signal. Here, NEUROD1 is linked to infection.