MAPT and Cognitive impairment: ICR mice administered 30 mg/kg of ketamine for 3 months have been found to exhibit increased dopamine levels (Tan et al., 2011), whereas C57 mice given the same dose of ketamine for 6 months have been found to show no cognitive impairment (Sun et al., 2011), even though the mice showed hyper-phosphorylation of tau and apoptosis in the prefrontal and entorhinal cortex (Yeung et al., 2010).