Andermann, M.

Balaguer-Ballester, Emili

Rupp, A.

Sebold, V.

Tabas, A.

Bournemouth University Research Online

Mean-field model of auditory cortex explains the differences inneuromagnetic fields evoked by dissonant and consonant dyadsAlejandro Tabas*1, Martin Andermann*2, Valeria Sebold2, Andre´ Rupp+2, and EmiliBalaguer-Ballester+131Faculty of Science and Technology, Bournemouth University, UK2Heidelberg University, Germany3Bernstein Center for Computational Neuroscience, Germany*equal contribution+joint last authorBernstein Conference 2016, BerlinPitch is a fundamental attribute of auditory sensation. A dyad is a sound presenting two simultaneouspitches; it is one of the most common perceptual scenarios in human auditory soundscape. However, theneuronal mechanisms underlying the perception of dyads are poorly understood.Dyads evoke a strong percept related to the ratio between the fundamental frequencies of the twosounds. Simple ratios (e.g. 3:2) evoke a consonant, pleasant sensation while complex (e.g 16:15) ratiosevoke a more dissonant percept. The N100m is a transient neuromagnetic response of the auditoryevoked fields observed in MEY recordings, sensitive to fundamental auditory properties such as pitchor timbre. The N100m is associated with activity in the antero-lateral Heschl’s gyrus (alHG) in humanauditory cortex (AC).First, we studied the effect of consonance and dissonance on the dynamics of the N100m using sixdifferent dyads built from two iterated rippled noise (IRN). We found a strong and significant correlationbetween the dissonance percept reported by human listeners (Fig. A, grey dashed lines) and the latencyof the N100m (Fig. A, blue lines).Figure 1: A) Observed (blue) and predicted (red) N100m latencies, reported consonance (grey), andharmonicity (green; measured as the similarity of the subcortical harmonic patterns separately elicitedby the two notes of the dyad). B) Observed (blue) and predicted (red) early auditory fields for twodyads.1The major goal of this study was to understand this correlation on the basis of the competitivedynamics of a cortical excitatory and inhibitory network of neural ensembles, endowing realistic neuraland synaptic parameters. Excitatory populations encode the pitch value, and receive direct inputsfrom an idealised model of subcortical processing, based on a well established model of the auditoryperiphery. In accordance with recent findings on the organisation of the mammal AC, inhibitory-to-excitatory connectivities follow a harmonic pattern that is crucial for cortical processing of pitch.The model was able to simultaneously decode the two single pitch values present within the stimuli,and to predict the latencies of the N100m evoked by the dyads (Fig. A, red lines; Fig. B compares fieldpredictions and observations).The model output suggests that the correlation of the N100m latency with consonance perceptionstems from the harmonic connectivity structure in AC. Simple frequency ratios (consonant dyads) pre-serve a greater harmonic relationship than more complex ratios (see green dashed lines in Fig. A), andthus are naturally faster to decode in cortex, eliciting an earlier N100m.In conclusion, our results suggest that the simulated competition dynamics in alHG provide a mech-anistic explanation of consonance perception.References[1] Balaguer-Ballester, E., Clark, N. R., Coath, M., Krumbholz, K., & Denham, S. L. (2009). Under-standing pitch perception as a hierarchical process with top-down modulation. PLoS ComputationalBiology, 5(3), e1000301.[2] Krumbholz, K., Patterson, R. D., Seither-Preisler, A., Lammertmann, C., & Lu¨tkenho¨ner, B. (2003).Neuromagnetic evidence for a pitch processing center in Heschl’s gyrus. Cerebral Cortex, 13(7),765–772.[3] Wong, K.-F., & Wang, X.-J. (2006). A recurrent network mechanism of time integration in perceptualdecisions. The Journal of Neuroscience, 26(4), 1314–1328.[4] Wang, X. (2013). The harmonic organization of auditory cortex. Frontiers in Systems Neuroscience,7, 114.[5] Zilany, M. S. a., Bruce, I. C., & Carney, L. H. (2014). Updated parameters and expanded simulationoptions for a model of the auditory periphery. The Journal of the Acoustical Society of America,135(1), 283–286.2

Mean-field model of auditory cortex explains the differences in neuromagnetic fields evoked by dissonant and consonant dyads

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