Neuromagnetic functional coupling during dichotic listening of speech sounds

Abstract

The present magnetoencephalography (MEG) study tested the hypothesis of a phase synchronization (functional coupling) of cortical alpha rhythms (about 6-12 Hz) within a "speech" cortical neural network comprising bilateral primary auditory cortex and Wernicke's areas, during dichotic listening (DL) of consonant-vowel (CV) syllables. Dichotic stimulation was done with the CV-syllable pairs /da/-/ba/ (true DL, yielded by stimuli having high spectral overlap) and /da/-/ka/ (sham DL, obtained with stimuli having poor spectral overlap). Whole-head MEG activity (165 sensors) was recorded from 10 healthy right-handed non-musicians showing right ear advantage in a speech DL task. Functional coupling of alpha rhythms was defined as the spectral coherence at the following bands: alpha 1 (about 6-8 Hz), alpha 2 (about 8-10 Hz), and alpha 3 (about 10-12) with respect to the peak of individual alpha frequency. Results showed an inverse pattern of functional coupling: during DL of speech sounds, spectral coherence of the high-band alpha rhythms increased between left auditory and Wernicke's areas with respect to sham DL, whereas it decreased between left and right auditory areas. The increase of functional coupling within the left hemisphere would underlie the processing of the syllable presented to the right ear, which arrives to the left auditory cortex without the interference of the other syllable presented to the left ear. Conversely, the decrease of inter-hemispherical coupling of the high-band alpha might be due to the fact that the two auditory cortices do not receive the same information from the ears during DL. These results suggest that functional coupling of alpha rhythms can constitute a neural substrate for the lateralization of auditory stimuli during DL.

Dynamic and Task-Dependent Encoding of Speech and Voice by Phase Reorganization of Cortical Oscillations

“…The different spatial distribution of the effects, and in particular the left hemispheric bias for the vowel but not the speaker task, indicates the involvement of distinct networks of brain areas. Based on this observation and the putative role of alpha oscillations in modulating functional connectivity between brain areas (von Stein et al, 2000;Kujala et al, 2007;Brancucci et al, 2008), we hypothesize that the observed phase reorganization operates at an interregional level. In particular, this reorganization may mediate temporal binding of distributed neural activity in distinct (auditory) cortical areas subserving the abstract representation of voice and speech (Formisano et al, 2008).…”

A primer on dichotic listening as a paradigm for the assessment of hemispheric asymmetry

“…However, the tendency for perceptual fusion strongly depends on the phonological properties of the contrasted stimuli even when they appear very similar (Repp, 1976). For example, when using plosives as initial phonemes, the voicing of the stimuli systematically affects the spectro-temporal overlap of the two auditory channels (Brancucci et al, 2008). Voiced syllables, such as /ba/ or /da/, are characterized by strong rhythmic vibrations of the vocal cord during articulation, while unvoiced syllables, such as /pa/ or /ta/, do not show such vibrations.…”

Test de escucha dicótica para niños hispanohablantes: validación de unas nuevas series de pares de palabras y de sílabas en castellano

“…Mediante magnetoencefalografía, empleando escucha dicótica de sílabas con voice onset time breve o largo, agrupadas en pares breve-largo, largo-largo, breve-largo y largo-breve para cada oído, parece que el acoplamiento de las diferentes bandas de ritmo alfa constituye el sustrato neurofisiológico de la lateralización de los estímulos verbales en tarea dicótica, al menos en lo que se refiere a la corteza auditiva y a la corteza asociativa implicada en el reconocimiento del material lingüístico [43]. En la actualidad, la resonancia magnética funcional durante la realización de tareas verbales es la referencia más precisa para estudiar la organización jerárquica interhemisférica e intrahemisférica del lenguaje en preescolares [44], e incluso en lactantes pequeños [45], y ha desplazado al test del amital sódico en estudios de jerarquización topográfica (no sólo interhemisférica, sino también intrahemisférica) de las funciones cerebrales superiores en adultos y en niños.…”