To further confirm that 5‐HT6R depletion contributed to the cognitive impairment observed in the null mice, we delivered exogenous 5‐HT6R to the brains of null mice by injecting mCherry plasmids packaged in adeno‐associated virus (AAV) and tagged with blue fluorescent protein (BFP) (AAV‐CMV‐MCS‐EFS‐tag BFP as the vector control and AAV‐CMV‐htr6‐mCherry‐EFS for 5‐HT6R) into the hippocampus of 5‐HT6R−/− mice. The gene discussed is HTR6; the disease is Cognitive impairment.