Research: Tuning in to speech
16 January 2008
Even when you’re doing nothing, your brain is very busy: neurons in many regions of the brain continue chattering in synchrony, with different groups operating at different frequencies. New research has shown that, in regions involved with listening and controlling the mouth, this chattering is tuned to the rhythms of human speech.
The scientists involved took advantage of differences between the areas that interpret sound on the left and right sides of the brain: the left side of the brain is attuned to sounds with faster rhythms than the right. Using simultaneous electroencephalogram readings and functional magnetic resonance imaging, the authors mapped brain activity linked to ongoing neuronal rhythms. They found that activity on each side of the brain correlated with the speech rhythm that hemisphere normally interprets. Thus, each side of the brain has activity that occurs with the same rate as the sound it recognises, even when there is nothing to listen to.
Coupling of endogenous activity to the same rhythms also occurred in the part of the brain that controls mouth movements during speech. The researchers therefore suggest that the tempo of human speech is the product of the pre-existing intrinsic rhythms in the brain.
Image: Artwork of the brain with halo of activity; Heidi Cartwright, Wellcome Images
References
Giraud AL et al. Endogenous cortical rhythms determine cerebral specialization for speech perception and production. Neuron 2007;56(6):1127-34.