Spatiotemporal characteristics of the neural activities processing consonant/dissonant tones in melody.

To identify neural correlates underlying melody processing, we measured MEG responses elicited by keynote and out-of-key tones at the end of musical phrases. These melodies were newly composed and unknown to the subjects. Significant enlargements of N1m/P2m peaks at about 120-160 ms were observed in response to dissonant (out-of-key) tones compared to those in response to consonant (keynote) tones. The equivalent current dipoles (ECD) of the N1m were localized in areas centered at bilateral primary auditory cortices in the superior surface of the temporal lobe. Following the N1m/P2m, a late component occurring at 280-530 ms was observed. As the latency proceeded, the location of ECD sources of the late component shifted in the right hemisphere, but not in the left hemisphere, from the supratemporal auditory cortex to a posterior inferior auditory association cortex around the superior temporal sulcus (STS). The grand mean locations of the ECDs for consonant and dissonant tones were separated at a peak period of 380-410 ms of the late component but converged to the same region around the STS in the last period of 440-530 ms. These observations suggest that the neural activities generating the N1m component in the bilateral auditory cortices may play a role in automatic detection of tonality mismatch based on the pitch analysis. The activities of the late component around the posterior part of the right STS are thought to be involved in the analysis of pitch-sequence, such as how the pitch changes temporally, as a pre-process of melody perception.