Study provides information on neural pathways involved in human word learning

Language is a uniquely human ability. The average vocabulary of a person consists of about thirty thousand words, although people show individual differences in their ability to learn a new language. It has long been believed that language learning depends on the integration of hearing and repeating words, but the neural mechanisms that lie behind learning new words remained unclear.

Now, a study made by researchers from the Cognition and Brain Plasticity Group of the Bellvitge Biomedical Research Institute (IDIBELL) and the University of Barcelona, together with experts from King's College London, provides information on neural pathways involved in human word learning. The key is in the arcuate fasciculus, a bundle of nerve fibers that connects auditory regions at the temporal lobe with the motor area located at the frontal lobe, in brain's left hemisphere. Individual differences in the development of connections in this bundle condition the ability to learn new words. Research results have been published on the journal Proceedings of the National Academy of Sciences (PNAS).

Artificial words

The study involved 27 healthy volunteers. Participants listened to nine artificial trisyllabic words with no meaning associated and with structures similar to Spanish words. There was a 25 millisecond pause among words; it was imperceptible but enough to help the learning of words in fluent speech. The nine words were randomly repeated 42 times.

In order to acquire additional information about brain's structure and function, two non-invasive MRI techniques were used. Before the word learning task, researchers registered structural brain images using a technique so-called 'diffusion tensor imaging'. This innovative technique enabled to reconstruct the white matter fibers that connect the different brain regions a posteriori. In addition, while participants listened to words, researchers recorded their brain activity using functional MRI, a procedure that makes a real-time and accurate detection of brain activity and the regions that are most active when an individual performs a given task.

After this language learning phase, participants heard a series of words and asked to identify the ones heard previously, during the learning phase. Researchers found a strong relationship between the ability to remember words and the structure of arcuate fasciculus, which connects two brain areas: Wernicke's area, related to auditory language decoding, and Broca's area, which coordinates the movements associated with speech and the language processing. In participants able to learn words more successfully their arcuate fasciculus was more myelinated. In addition, activity between these two regions was more coordinated in these participants.

Source: http://www.ub.edu