Presentation
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Multiple theta-gamma interactions emerge in the auditory cortex during speech perception.
Poster C88 in Poster Session C, Wednesday, October 25, 10:15 am - 12:00 pm CEST, Espace Vieux-Port
Víctor J. López-Madrona1, Benjamin Morillon1, Caroline Chaux2, Daniele Schon1, Christian G. Bénar1; 1Institut de Neurosciences des systèmes, Aix-Marseille Université (FRANCE), 2Aix-Marseille Univ, CNRS, I2M, Marseille (FRANCE)
Frequency division multiplexing in the auditory cortex is observed during speech processing. High-gamma activity (~120 Hz) follows the fundamental frequency (F0) of the voice in speech while low-gamma dynamics (~40 Hz) seem more related to phonetic processing. The amplitude of both is coupled to the phase of theta oscillations (4-8 Hz), which track the speech acoustic rhythm. However, the functional role of such phase-amplitude coupling is a matter of debate. In this work, we recorded the electrophysiological activity from the auditory cortex in epileptic patients implanted with intracerebral EEG (iEEG) electrodes. The patients performed a natural speech perception task, passively listening to a 10-minutes length story. We analyzed the functional connectivity (i) between the speech envelope waveform and the cortical activity, and (ii) between different regions of the auditory cortex. Importantly, we measured the cross-frequency directionality between the amplitude of low- and high-gamma oscillations and the phase of the theta rhythm, testing different hypotheses that have been proposed for speech encoding. We show that both (low- and high-) gamma and theta oscillations in the auditory cortex are driven by the speech envelope. Interestingly, a directed functional connectivity emerges from high-gamma to theta oscillations in the brain, a feature that is not present in the speech signal. This suggests that both (theta and gamma) brain rhythms are not only tracking speech but are related to two different neuronal mechanisms that go beyond the temporal acoustic structure of the auditory input (phonemes & syllables). Overall, we present new insights in the role of auditory theta-gamma coupling in speech processing, and how the information flow between oscillations informs us about different steps of speech parsing and decoding in the brain.
Topic Areas: Speech Perception,