July 23, 2013
Research Sheds New Light On Our Unique Ability To Learn Languages
redOrbit Staff & Wire Reports - Your Universe Online
A neural pathway unique to humans allows us to learn new words and languages, European scientists reported on Monday.
Experts have long believed language acquisition - a distinctively human ability - depends on the integration of information between motor and auditory representation of words in the brain, although the precise neural mechanisms behind this interaction remained unclear.
In the current study, researchers from the group of Cognition and Brain Plasticity at the Bellvitge Biomedical Research Institute (IDIBELL), the University of Barcelona and King's College of London, discovered for the first time that our ability to learn new words is based on efficient communication between areas of the left hemisphere of the brain that control movement and hearing.
The key is in the arcuate fasciculus, a collection of nerve fibers that connect auditory regions at the temporal lobe with the motor area located at the frontal lobe in the left hemisphere of the brain.
The arcuate fasciculus is what allows the 'sound' of a word to be connected to the regions responsible for its articulation. Differences in the development of these auditory-motor connections may explain differences in people's ability to learn words, the researchers said.
The study involved 27 healthy volunteers who listened to nine artificial trisyllabic words with no meaning associated and with structures similar to the words of the Spanish language. Between each word there was a 25 millisecond pause - imperceptible but enough to help the learning of words in fluent speech. The nine words were randomly repeated 42 times.
Before conducting the task of word learning, researchers registered structural brain images using an innovative technique known as diffusion tensor imaging, which reconstructed a posteriori - the white matter fibers that connect the different brain regions.
The researchers then used functional MRI to monitor in real time the participants' brain activity as they listened to words to observe the regions of the brain that are most active when participants performed a given task. After this phase of language learning, participants heard a series of words and were asked to identify those they had heard during the learning phase.
The researchers observed a strong relationship between the ability to remember words and the structure of arcuate fasciculus, which connects two brain areas: the territory of Wernicke, related to auditory language decoding, and Broca's area, which coordinates the movements associated with speech and the language processing.
The participants who were able to learn words better had arcuate fasciculus that were more myelinated, meaning the nervous tissue facilitated faster conduction of the electrical signal. The synchronization between the activity of the regions connected by this fasciculus was also higher in these participants, the researchers said.
Diana Lopez-Barroso at the University of Barcelona, the study's first author, said the research sheds new light on the unique ability of humans to learn a language, since there are different connection models between these brain regions in other species.
The work may also be useful in the rehabilitation of people with injuries at the arcuate fasciculus, she added.
"In this case, we can find another way to get to the same place", said Lopez-Barroso.
This could be the ventral pathway, another bundle of nerve fibers that also connects Broca's and Wernicke's territories but that passes through lower brain areas, she said.
"The ventral pathway, which is more related to the processing of the meaning of words, would give a semantic support to word learning in people with injuries."
Study co-author Dr. Marco Catani from King's College London Institute of Psychiatry said, "Often humans take their ability to learn words for granted. This research sheds new light on the unique ability of humans to learn a language, as this pathway is not present in other species.
"The implications of our findings could be wide ranging - from how language is taught in schools and rehabilitation from injury, to early detection of language disorders such as dyslexia. In addition these findings could have implications for other disorders where language is affected such as autism and schizophrenia.
"Now we understand that this is how we learn new words, our concern is that children will have less vocabulary as much of their interaction is via screen, text and email rather than using their external prosthetic memory. This research reinforces the need for us to maintain the oral tradition of talking to our children."
The study is published in the journal Proceedings of the National Academy of Sciences.