Neurogenesis in the subventricular zone (SVZ) is altered in neurodegenerative diseases and activated by deep brain stimulation, new research suggests. Analysis of postmortem brain tissue showed that the SVZ was thinner in people with Parkinson disease (PD) than in people without neurodegenerative disease. By contrast, the SVZ was thicker in people with Huntington disease and in people with PD who had received deep brain stimulation. In both cases, thickening of the SVZ was accompanied by a high density of adult neural stem cells, indicating activation of neurogenesis.