Possible neuronal refractory or recovery artifacts associated with recording the mismatch negativity response

The mismatch negativity (MMN) is an event-related potential that involves a negative voltage shift of baseline electroencephalographic (EEG) activity in the approximate latency window of the N1 and P2 cortical potentials in response to new or novel sounds. The MMN is present at birth and has been hypothesized to serve as an automatic preconscious detector of changes in the auditory environment. Research paradigms used to extract the MMN response from EEG activity have a potential problem related to neuronal refractoriness or recovery. Both N1 and P2 are known to increase in amplitude with longer interstimulus intervals (ISIs). The MMN extraction procedures involve mathematical subtraction of waveforms elicited by standard sounds (with short ISIs) from those recorded to rare deviant sounds (with longer ISIs). Any ISI-dependent amplitude changes in N1 and/or P2 could therefore alter the morphology of the resulting difference wave and lead to misinterpretation of the nature of the underlying MMN generators. We tested 12 young females and found that the MMN can be influenced by ISI-dependent refractory effects that may modify the waveform morphology. This has important clinical implications since the MMN is being investigated as an assessment tool.