A study (Yeung et al., 2010) found that after 6 months of ketamine administration, the positive sites of hyperphosphorylated tau protein significantly increased in the prefrontal lobe and entorhinal cortex of mice and monkeys, and the long-term toxicity of ketamine may involve a neurodegenerative process similar to aging and/or Alzheimer’s disease. This evidence concerns the gene MAPT and Alzheimer disease.