Neural representation for tonality of three-tone chord in rat auditory cortex

Some three-tone chords have tonality such as major or minor key. These keys are associated with some specific emotion such as delight or sadness, thus three-tone chords are thought to have emotional qualia. In this study, we targeted phase locking value (PLV) of local field potential (LFP) in rat auditory cortex and investigated whether PLV represents tonality of the three-tone chord. We construct seven three-tone chords consisting of three pure tones; two major chords, two minor chords, and three chords representing no specific tonality. A microelectrode array recorded LFPs from the fourth layer of the auditory cortex of anesthetized rats, while we presented these three-tone chords. From the recorded LFPs, we calculated PLVs in 5 bands (theta, 4 – 8 Hz; alpha, 8 – 14 Hz; beta, 14 – 30 Hz; low gamma, 30 – 40 Hz; high gamma, 60 – 80 Hz) and compared them. As a result, in alpha, low gamma and high gamma band, PLV was larger in the major chords than the minor chords. These results suggest that the phase synchrony within the auditory cortex represents the tonality of three-tone chord.