A 35-year-old male with schizophrenia has been stable on olanzapine 20 mg daily for 3 years but has gained 45 pounds with a new HbA1c of 6.3% (prediabetes). The PMHNP initiates a cross-titration to aripiprazole to reduce metabolic risk. Over 3 weeks, olanzapine is tapered from 20 mg to 10 mg while aripiprazole is titrated to 15 mg. At this point, the patient's family reports he has become more guarded, started expressing paranoid ideas about his neighbors, and has been talking to himself, symptoms that had been absent for years. Which of the following best explains the re-emergence of psychotic symptoms during this cross-titration?