Potential participants will be receiving stables doses of clozapine for a minimum period of 6 months before entry into the study. Clozapine was selected because i) the majority of our studies in mouse models were performed after chronic treatment with this atypical antipsychotic, and ii) the investigators' data in postmortem human brain samples of subjects with antemortem diagnosis of schizophrenia suggest up-regulation of HDAC2 in frontal cortex of schizophrenic subjects treated with atypical, but not typical, antipsychotic drugs.