Mismatch negativity (MMN), first described by Risto Naatanen in the late 1970s, is now known as a key brain phenomenon, reflecting its ability to detect differences in the presented sensory stimuli. Although MMN has been widely studied in both humans and other mammals, the phenomenon has also been increasingly examined in non-mammalian species in recent years. Here, we discuss the role of MMN as an evolutionarily conserved phenotype across taxa, and its translational significance in neuroscience. Despite challenges in studying MMN in non-mammalian species (especially due to methodological limitations and differences in sensory processing), these model organisms offer important insights into brain sensory and cognitive processing that can have further clinical implications in diagnosing and treating brain disorders.