Related Experiment Videos
Hemispheric lateralization in the cortical motor preparation for human vocalization.
1Department of Neurology, Division of Neuroscience, Graduate School of Medicine, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8655, Japan.
Summary
This study reveals how the brain prepares for speech. Cortical stimulation showed a shift in brain activity dominance from the left to the right hemisphere just before vocalization.
Area of Science:
- Neuroscience
- Cognitive Neuroscience
- Speech Production
Background:
- Understanding the neural mechanisms underlying speech production is crucial for diagnosing and treating speech disorders.
- The role of cortical processing during the preparation phase of vocalization remains incompletely understood.
Purpose of the Study:
- To investigate cortical information processing during the preparation of human vocalization.
- To determine the involvement of specific cortical areas and hemispheric lateralization during speech preparation.
Main Methods:
- Transcranial magnetic stimulation (TMS) was applied over the cortex during vocalization preparation in response to visual cues.
- Reaction time (RT) of vocalization was measured with and without TMS.
- TMS was delivered at different time points before the expected onset of voice (EOV) and over different cortical areas (bilateral motor areas, supplementary motor cortex).
Main Results:
- TMS prolonged vocalization RT when applied up to 150-200 msec before EOV, with the largest delays (10-20%) over bilateral motor areas.
- During the early prevocalization phase (50-100 msec before EOV), left motor area stimulation caused a slightly larger delay than right motor area stimulation.
- During the late prevocalization phase (0-50 msec before EOV), right motor area stimulation caused a significantly larger delay, indicating a shift in hemispheric predominance.
Conclusions:
- Cortical preparation for vocalization involves alternating hemispheric lateralization between bilateral motor cortices.
- A mild left hemispheric predominance in the early phase switches to a robust right hemispheric predominance in the late phase before voice onset.
- The findings suggest involvement of the motor representation of respiratory muscles and the supplementary motor cortex in vocalization preparation.