Investigators used BrdU (indicator of neural proliferation) and DCX (microtubule associated protein and indicator of neurogenesis) to mark NPCs in the hippocampal dentate gyrus. Older mice housed with EE conditions for 21 weeks had increased BrdU + cells compared to the non-EE group. Enrichment also ameliorated structural deficits in older HD mice, resulting in increased neuronal migration and longer neurites. The gene discussed is DCX; the disease is Huntington disease.