Life Sciences Division

Infant brains visualised by brain imaging

In the very first months of life, the human brain is already specialised for language acquisition and mother tongue memorisation. These conclusions were drawn from the first detailed functional magnetic resonance imaging (fMRI) study of the response of infant brains to speech. They are the result of joint research conducted at the Necker Children’s Hospital and the Frédéric Joliot Hospital Service between CNRS, CEA, Inserm and AP-HP teams. This work was published in the journal Science of Friday 6 December.

©CEA/Inserm/S. Dehaene

The adult human brain possesses a high degree of anatomic and functional specialisation for language processing. We know that a considerable proportion of the mechanisms of language learning are set in place during the first year of life, and that infants soon recognise phonemes and prosody and can segment into words the continuous signal formed by speech. To understand how these abilities appear and become organised in the brain a team of French researchers from the CNRS, Inserm, CEA and Public Hospitals have just published the first detailed functional magnetic resonance imaging (fMRI) study of the response of three-month-old infant brains to speech sounds.

Magnetic resonance is a completely harmless exploration method that has been used in neuropaediatrics for more than twenty years. The more recent functional magnetic resonance imaging (fMRI) makes it possible to visualise areas of the brain that become active in response to a stimulus.
Images of brain activation in infants were collected while they listened to an audio recording of a story being told by a woman, played in 20-second segments alternating with 20-second periods of silence. The novelty of the experiment was that the audio recording was played both normally and backwards. The sound heard backwards does not have the universal properties of human language and so the children could not recognise characteristic sounds. By comparing the brain areas activated when the recording was heard normally and backwards it was possible to determine whether certain areas of the brain were already specialised in the recognition of mother tongue language features.

The results obtained show:

• Like in adults, a marked asymmetry of the activation in favour of the left hemisphere. The fact that this left laterality is already present at age three months strongly suggests the existence of a genetic bias in the organisation of language-specialised brain areas.
• An organisation of the brain into functional regions comparable to those observed in adults in similar tasks. However, the observation of a right frontal activation, present in adults but in tasks more complex than merely listening to speech strings, suggests that active mechanisms of attention and effort are at work in language acquisition.
• The presence, as early as age three months, of language memory. The activation profiles of deeply sleeping and awake infants were compared, and showed that a particular area of the right prefrontal cortex was specifically and more strongly activated in awake infants when the recording was played normally rather than backwards. In adults, this brain area is activated when retrieving memorised verbal information. Very young infants may therefore already be able to memorise sound patterns of their mother tongue, well before they can produce language, and even though the ability to remember words appears only at age seven months.

Language acquisition is thus the result of a gradual specialisation of a genetically pre-determined network, under the influence of active mechanisms of attention and memory directed towards the language heard in the infant's environment.

In the future this functional MRI method should also make it possible to visualise the development of other brain functions in infants (sight, hearing, movement) and their pathology.

¹ - Magnetic resonance is a completely harmless exploration method that has been used in neuropaediatrics for more than twenty years. The more recent functional magnetic resonance imaging (fMRI) make it possible to visualise areas of the brain that become active in response to a stimulus.
² – Department of Paediatric Radiology, Prof. Brunelle
³ – The Frédéric Joliot Hospital Service of the CEA is currently the only research unit in Europe that combines the different methods of human non-invasive functional exploration.