November 30th – Anne-Lise Giraud – Speech processing with (and without) cortical oscillations

Neuroscience Seminar Series

Friday, November 30th, 2018 at 11:30
Salle des Conférences (R229)
Centre Universitaire des Saints-Pères
45 rue des Saints-Pères 75006 Paris

Anne-Lise Giraud, University of Geneva, Switzerland

Title: Speech processing with (and without) cortical oscillations

Perception of connected speech relies on accurate syllabic segmentation and phonemic encoding.
These processes are essential because they determine the building blocks that we can manipulate
mentally to understand and produce speech. Segmentation and encoding might be underpinned by
specific interactions between the acoustic rhythms of speech and coupled neural oscillations in the
theta and low-gamma band. To address how neural oscillations interact with speech and intervene
in phonological processing, we developed neurocomputational models involving theta and gamma
oscillations. By comparing models with and without oscillations, we establish that recognition
performance are generally better with oscillations. Based on these models we hypothesized that
if low-gamma oscillations are disrupted or shifted in frequency speech perception would still be
possible, but phonemic units within syllables would have an abnormal format, potentially causing
difficulties to map idiosyncratic phonemic representations with universal ones, as those we are
taught to become aware of when learning to read. A disruption of the auditory gamma oscillation
could hence account for some aspects of the phonological deficit in dyslexia. Using MEG, and
EEG combined with fMRI, and neurostimulation, we found that dyslexia is associated with a
specific deficit in low-gamma activity in auditory cortex, and that this deficit alone accounts
for several facets of the disorder. Recently, we further found that boosting 30Hz neural activity
in left auditory cortex using transcranial alternative current stimulation selectively improves
phonological performance and reading efficiency. Altogether these results attempt to establish a
causal role of oscillatory processes in speech perception.

Those interested in meeting with the speaker please contact

sophie.l.bouton@gmail.com

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