A 47-year-old female with major depressive disorder has failed adequate trials of sertraline, escitalopram, and duloxetine over the past two years. She has no history of seizure disorder, eating disorder, or substance use disorder. The PMHNP discusses dextromethorphan-bupropion (Auvelity) as a next-step treatment. The patient asks how this medication works differently from her previous antidepressants. Which of the following best describes the unique mechanism of this combination?