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The present study investigated the influence of musical expectations on auditory representations in musicians and non-musicians using magnetoencephalography (MEG). Neuroscientific studies have demonstrated that musical syntax is processed in the inferior frontal gyri, eliciting an early right anterior negativity (ERAN), and anatomical evidence has shown that interconnections occur between the frontal cortex and the belt and parabelt regions in the auditory cortex (AC). Therefore, we anticipated that musical expectations would mediate neural activities in the AC via an efferent pathway. To test this hypothesis, we measured the auditory-evoked fields (AEFs) of seven musicians and seven non-musicians while they were listening to a five-chord progression in which the expectancy of the third chord was manipulated (highly expected, less expected, and unexpected). The results revealed that highly expected chords elicited shorter N1m (negative AEF at approximately 100 ms) and P2m (positive AEF at approximately 200 ms) latencies and larger P2m amplitudes in the AC than less-expected and unexpected chords. The relations between P2m amplitudes/latencies and harmonic expectations were similar between the groups; however, musicians’ results were more remarkable than those of non-musicians. These findings suggest that auditory cortical processing is enhanced by musical knowledge and long-term training in a top-down manner, which is reflected in shortened N1m and P2m latencies and enhanced P2m amplitudes in the AC.

In real music, the original melody may appear intact, with little elaboration only, or significantly modified. Since a melody is most easily perceived in music, hearing significantly modified melody may change a brain connectivity. Mozart KV 265 is comprised of an original melody of “Twinkle Twinkle Little Star” with its significant variations. We studied whether effective connectivity changes with significantly modified melody, between bilateral inferior frontal gyri (IFGs) and Heschl’s gyri (HGs) using magnetoencephalography (MEG). Among the 12 connectivities, the connectivity from the left IFG to the right HG was consistently increased with significantly modified melody compared to the original melody in 2 separate sets of the same rhythmic pattern with different melody ( p = 0.005 and 0.034, Bonferroni corrected). Our findings show that the modification of an original melody in a real music changes the brain connectivity. Significant statements Our data show how a regional connectivity changes when the original melody is intact or significantly modified, consistent in two different sets of variations with the same rhythmic patterns but with the different melody pattern. The present study employed real music of Mozart’s Variation KV 265 as musical stimuli, dissected musical elements in each variation, and devised the two comparable sets of variation, which have the same rhythmic pattern but different melody. We exploited naturalistic conditions in real music instead of devising artificial conditions, and successfully demonstrated how variations of melody in real music change a regional connectivity in the brain.

Recent studies have reported that early right anterior negativity (ERAN) and its magnetic counterpart (ERANm) are evoked by harmonic irregularity in Western tonal music; however, those studies did not control for differences of melody. Because melody and harmony have an interdependent relationship and because melody (in this study melody is represented by the highest voice part) in a chord sequence may dominate, there is controversy over whether ERAN (or ERANm) changes arise from melody or harmony differences. To separate the effects of melody differences and harmonic irregularity on ERANm responses, we designed two magnetoencephalography experiments and behavioral test. Participants were presented with three types of chord progression sequences (Expected, Intermediate, and Unexpected) with different harmonic regularities in which melody differences were or were not controlled. In the uncontrolled melody difference experiment, the unexpected chord elicited a significantly largest ERANm, but in the controlled melody difference experiment, the amplitude of the ERANm peak did not differ among the three conditions. However, ERANm peak latency was delayed more than that in the uncontrolled melody difference experiment. The behavioral results show the difference between the two experiments even if harmonic irregularity was discriminated in the uncontrolled melody difference experiment. In conclusion, our analysis reveals that there is a relationship between the effects of harmony and melody on ERANm. Hence, we suggest that a melody difference in a chord progression is largely responsible for the observed changes in ERANm, reaffirming that melody plays an important role in the processing of musical syntax.