How the brain decodes music and speech

Recognizing a melody or understanding a phrase does not activate the same areas of the brain, the two hemispheres are not mobilized in the same way, which the researchers already knew. However, this asymmetrical specialization was not explained at the physiological and neuronal level.

The sound comes from a complex set of vibrations of the'air who when they arrive in the ear internal at the cochlea, are discriminated there according to their speed : at all times, slow vibrations are translated into low tones and fast vibrations into high tones. This allows to represent the sound according to two dimensions: the spectral dimension (frequency) and the time dimension (time). These two auditory dimensions are fundamental because it is their simultaneous combination which stimulates the neurons of cortex auditory. The latter would in particular make it possible to discriminate the sounds relevant to the individual, such as the sounds used for the communication which allow exchange and understanding between individuals.

The language and the music constitute in humans the main uses of sound and the most complex at the cognitive level. The left hemisphere is mainly involved in the recognition of the language, while the right hemisphere is mainly involved in that of music. However, the physiological and neuronal basis of this asymmetry was still unknown.

A research team co-led by Inserm researcher Benjamin health at the Institute for Systems Neurosciences (Inserm / Aix-Marseille University), in collaboration with researchers from the Montreal Neurological Hospital Institute of McGill University, used an innovative approach to understanding how the language and music are decoded within each cerebral hemisphere in humans. These results to appear in Science.

Different receptivity to the components of sound

The researchers recorded 10 phrases each sung by a soprano on 10 new melodic tunes composed for the occasion. These 100 recordings, in which melody and speech are dissociated, were then distorted by reducing the amount of information present in each dimension of the sound. 49 participants were asked to listen to these distorted paired recordings, and to determine whether they were identical in melody or text. The experiment was carried out in French and English, in order to observe whether the results were reproducible in different languages. By clicking on this link, a audio Review demonstration available to participants is available.

The research team found that, regardless of the language, when the time information was distorted the participants were able to recognize the melody, but had difficulty identifying the content of the text. Conversely, when the spectral information was distorted, they were able to recognize the text but had trouble recognizing the melody.

Observation by imagery by resonance functional (FMRI) of the'neural activity of the participants showed that, in the left auditory cortex, the activity varied according to the sentence presented but remained relatively stable from one melody to another, while in the right auditory cortex, the activity varied according to the melody presented but remained relatively stable from one sentence to another.

The specialization of each cerebral hemisphere

In addition, when the temporal information was degraded, only the neural activity of the left auditory cortex was affected, while the degradation of spectral information only affected the activity of the right auditory cortex. Finally, participants' performance in the recognition task could be predicted only by observing the neural activity of these two areas.

"These results indicate that, in each cerebral hemisphere, neuronal activity is dependent on the type of sound information, specifies Benjamin health. If the temporal information is secondary to recognize a melody, it is on the contrary essential to the good recognition of the language. Conversely, if the spectral information is secondary to recognize the language, it is essential to recognize a melody. "

The neurons of the left auditory cortex would therefore be mainly receptive to language thanks to their better ability to process temporal information, while those of the right auditory cortex would be receptive to music thanks to their better ability to process spectral information. . " Hemispheric specialization could be the means for the nervous system to optimize the respective processing of the two communication sound signals that are speech and music ”, concludes Benjamin health.

This will also interest you

"Children's brains, endless potential?" ": The brain develops slowly The documentary Children's Brain, endless potential? by Stéphanie Brillant, broadcast by Jupiter Films and released in France on May 23, questions psychotherapists and neurophysiologists, all from North America, on brain development from birth to adulthood. These specialists draw advice for parents and educators.

Did you like this article ? Don't hesitate to share it with your friends and help us to promote ABSMARTHEALTH :)! The editorial team thanks you.