Monday September 11 2006
CEA
The activation of Broca’s area in infants is surprising. This area governs functions that are still immature (verbal production) or inexistent (syntactic processing) at 3 months of age. The work carried out by the team headed by Ghislaine Dehaene shows that three-month-old infants, although they are incapable of repeating whole sentences, already possess the neural circuitry that enables them to identify certain repeated items in an utterance.
In addition, recent work has shown that in the equivalent of this region in macaque monkeys there are special neurones, named ‘mirror’ neurones, which are activated not only when an action is being performed, but also whenever the monkey sees or hears a fellow monkey doing the same action. Broca’s area may thus be essential for unifying the different representations of speech; motor when speaking, visual when seeing speech being produced, and auditory when speech is being heard. This enables the infant to make full use of the varied sensory information it receives.
Can the organisation of the infant brain explain the rapid acquisition of a first language?
CEA
Why are humans the only species that are able to master a complex language? Why is it that infants learn their first language so quickly, when adults find it so difficult to learn a second language? The answers to these questions may lie in the specific organisation of the human brain and in close collaboration among regions with different but complementary functions. These are the hypotheses advanced by the research teams at Inserm, the CEA, Paris Hospitals and the CNRS. Their work extends the conclusions drawn in 2002 by the same researchers, who demonstrated that infants activated the same brain areas as adults when they heard speech. Today their results show that the adult organisation, which presents a close collaboration between comprehension areas (the temporal area, including Wernicke’s area and verbal production areas (Broca’s area in the left lower frontal region), is already present in infants even before they learn to speak. These new findings were recently published in the online edition of the Proceedings of the National Academy of Science (PNAS).
Paris, 6 September 2006
Press release
Press release
The study was conducted by Ghislaine Dehaene and her team (Inserm Unit 562 ‘Cognitive Neuroimaging’) at the CEA, in the Joliot Curie Hospital Service. It consisted in visualising the organisation of the brain regions activated by listening to short utterances (lasting only 2 s) using functional nuclear magnetic resonance (fMRI)1. This work was carried out in 10 infants aged 3 month (4 girls and 6 boys) at the Necker children's hospital (AP-HP)
He upper temporal region is crucial for the comprehension of language. It contains the primary auditive cortex (C Aud), which receives information from the ear, and Warnicke’s area in its posterior part.
The lower frontal region (Broca’s area) is involved in adult verbal production, short-term memory and the integration of syntax. The motor regions that govern articulation are located just behind it.
Arcuate fasciculus: the main neural pathway connecting the regions of language production and comprehension. Its maturation continues up to puberty.
Uncinate fasciculus: this connects the frontal and temporal lobes.
1 Nuclear magnetic resonance imaging is an entirely harmless technique based on the magnetic properties of tissues. It has been used for more than twenty years in paediatric neurology. The more recent functional magnetic resonance imaging (fMRI) can be used to visualise brain areas that become active in response to a stimulus (e.g., a sound or an image).
Using fMRI researchers have found that these utterances induce a cascade of activation in the temporal and frontal areas. The regions closest to the auditive cortex are activated at the start of the utterance. Other more distant areas, such as Broca’s area, respond more slowly (see diagram). This progressive response may reflect the stepwise integration of the sound signal into longer and longer units, enabling the infant to process the phrasal structure of the utterance.
The research team also found that the response in Broca’s area was stronger when the utterance was repeated. We know that in adults this region is crucial for short-term verbal memory (when we remember a telephone number for example). This memory process seems to rely on a silent repetition of the items to be remembered.
The activation of Broca’s area in infants is surprising. This area governs functions that are still immature (verbal production) or inexistent (syntactic processing) at 3 months of age. The work carried out by the team headed by Ghislaine Dehaene shows that three-month-old infants, although they are incapable of repeating whole sentences, already possess the neural circuitry that enables them to identify certain repeated items in an utterance.
In addition, recent work has shown that in the equivalent of this region in macaque monkeys there are special neurones, named ‘mirror’ neurones, which are activated not only when an action is being performed, but also whenever the monkey sees or hears a fellow monkey doing the same action. Broca’s area may thus be essential for unifying the different representations of speech; motor when speaking, visual when seeing speech being produced, and auditory when speech is being heard. This enables the infant to make full use of the varied sensory information it receives.
There remain the questions of whether other stimuli are also processed in this way, and why it is that only human babies learn to speak. Brian imaging will continue to help us find the answers.
For more information
For more information
• Source
“Functional organization of perisylvian activation during presentation of sentences in preverbal infants”
Ghislaine Dehaene-Lambertz1,2,7, Lucie Hertz-Pannier3,5,7, Jessica Dubois4,7, Sebastian Mériaux4,7, Alexis Roche4,7, Mariano Sigman1,7, Stanislas Dehaene1,6,7
1 Inserm Unit 562, CEA - SHFJ, 4 place du Général-Leclerc, 91400 Orsay
2 Paediatric Neurology, Kremlin-Bicêtre Teaching Hospital, AP-HP, Paris
3 Paediatric Radiology, Necker Children’s Teaching Hospital, AP-HP, Paris
4 CEA, UNAF, 4 place du Général-Leclerc, 91400 Orsay
5 INSERM, U663, University of Paris 5, Paris
6 Collège de France, Paris
7 IFR49, Orsay
PNAS, online publication, week of 4 September 2006
“Functional organization of perisylvian activation during presentation of sentences in preverbal infants”
Ghislaine Dehaene-Lambertz1,2,7, Lucie Hertz-Pannier3,5,7, Jessica Dubois4,7, Sebastian Mériaux4,7, Alexis Roche4,7, Mariano Sigman1,7, Stanislas Dehaene1,6,7
1 Inserm Unit 562, CEA - SHFJ, 4 place du Général-Leclerc, 91400 Orsay
2 Paediatric Neurology, Kremlin-Bicêtre Teaching Hospital, AP-HP, Paris
3 Paediatric Radiology, Necker Children’s Teaching Hospital, AP-HP, Paris
4 CEA, UNAF, 4 place du Général-Leclerc, 91400 Orsay
5 INSERM, U663, University of Paris 5, Paris
6 Collège de France, Paris
7 IFR49, Orsay
PNAS, online publication, week of 4 September 2006