A chimeric non-human mammal disease model, wherein (1) at least 30% of all the glial cells in the corpus callosum of the chimeric non-human mammal are human glial cells, and/or (2) at least 5% of all of the glial cells in the white matter of the brain and/or brain stem of the chimeric non-human mammal are human glial cells, and wherein the human glial cells comprise a combination of a first group of human glial cells tagged with a first label and a second group of human glial cells tagged with a second label that is distinguishable from the first label.