Adaptation and Mismatch Negativity (MMN): Comparing First vs. Subsequent Repetitions in a Roving EEG Paradigm with Minimized Expectations

Adaptation is defined as reduced neural activation following repeated stimulus presentation. While previous EEG studies used either one repetition or multiple repetitions to elicit adaptation in event-related potentials (ERP), it is unclear whether adaptation differs between initial and subsequent repetitions. In addition, multiple repetitions were used in mismatch negativity (MMN) experiments to measure deviance detection, but how adaptation contributes to the MMN remains unclear. Therefore, in the current study, 37 healthy adults participated in an EEG experiment with a pure tone roving paradigm and a random stimulus arrangement to minimize expectations. The amplitudes and latencies were traced along with the first ten tones in different components of the auditory ERP, including P1, N1, and P2, to examine the relationship between adaptation and the number of repetitions. Results showed a slight increasing adaptation effect in the P1, an L-shaped adaptation in the N1 with a large decrease after the first repetition, and a continuous, linear amplitude increase in the P2, possibly indicating memory trace formation. Regression results showed that the peak amplitudes of the N1 initial adaptation and the P2 subsequent adaptation significantly explained the variance in the MMN amplitude. The results indicate distinct adaptation patterns for multiple repetitions in different components and suggest that the MMN combines two processes as indicated by the initial adaptation in the N1 and a continuous memory trace effect in the P2. Separating the two processes may be relevant for models of cognitive processing and clinical disorders.