Mismatch response (MMR) in neonates: Beyond refractoriness

• Mismatch Negativity like response is elicited in newborn infants.
• Neonatal counterpart for MMN persists when controlling for N1 refractoriness effects.
• Adult MMN and neonatal MMR reflect similar functions but differ in morphology.

In the adult auditory system, deviant detection and updating the representation of the environment is reflected by the event-related potential (ERP) component termed the mismatch negativity (MMN). MMN is elicited when a rare-pitch deviant stimulus is presented amongst frequent standard pitch stimuli. The same stimuli also elicit a similar discriminative ERP component in sleeping newborn infants (termed the mismatch response: MMR). Both the MMN and the MMR can be confounded by responses generated by differential refractoriness of frequency-selective neural populations. Employing a stimulus paradigm designed to minimize this confounding effect, newborns were presented with sequences of pure tones under two conditions: In the oddball block, rare deviant tones (500 Hz; 10%) were delivered amongst frequent standards (700 Hz; 90%). In the control block, a comparison tone (500 Hz) was presented with the same probability as the deviant (10%) along with the four contextual tones (700 Hz, 980 Hz, 1372 Hz, 1920.8 Hz; 22.5% each). The significant difference found between the response elicited by the deviant and the comparison tone showed that the response elicited by the deviant in the oddball sequences cannot be fully explained by frequency-specific refractoriness of the neural generators. This shows that neonates process sounds in a context-dependent manner as well as strengthens the correspondence between the adult MMN and the infant MMR.