As a postgrad in the Department of Developmental Neurobiology at Guy’s Hospital, I met Samuel Weiss, who first discovered stem cells in the adult mammalian brain back in 1992. Sam spent a month or so in our lab, learning how to dissect the hindbrain from chick embryos.
Stem cell research has come a long way since 1992. A recent Neuron paper describes the identification in the human brain of stem cells which can give rise to both neurons and oligodendrocytes. The cells express a platelet-derived growth factor receptor (PDGFR) and differentiate into oligodendrocytes in response to PDGF.
(Via Pure Pedantry, where you can read more about it.)