From our very first years, we are intrinsically motivated to learn new words and their meanings. First language acquisition occurs within a permanent emotional interaction between parents and children. However, the exact mechanism behind the human drive to acquire communicative linguistic skills is yet to be established.

In a study published in the journal Current Biology, researchers from the University of Barcelona (UB), the Bellvitge Biomedical Research Institute (IDIBELL) and the Otto von Guericke University Magdeburg (Germany) have experimentally proved that human adult word learning exhibit activation not only of cortical language regions but also of the ventral striatum, a core region of reward processing. Results confirm that the motivation to learn is preserved throughout the lifespan, helping adults to acquire a second language.

Researchers determined that the reward region that is activated is the same that answers to a wide range of stimuli, including food, sex, drugs or game. "The main objective of the study was to know to what extent language learning activates subcortical reward and motivational systems," explains Pablo Ripollés, PhD student at UB-IDIBELL and first author of the article. "Moreover, the fact that language could be favoured by this type of circuitries is an interesting hypothesis from an evolutionary point of view," points out the expert.

According to Antoni Rodríguez Fornells, UB lecturer and ICREA researcher at IDIBELL, "the language region has been traditionally located at an apparently encapsulated cortical structure which has never been related to reward circuitries, which are considered much older from an evolutionary perspective." "The study -- he adds -- questions whether language only comes from cortical evolution or structured mechanisms and suggests that emotions may influence language acquisition processes."

Subcortical areas are closely related to those that help to store information. Therefore, those facts or pieces of information that awake an emotion are more easily to remember and learn.

Motivation for learning a second language

By using diffusion tensor imaging, UB-IDIBELL researchers reconstructed the white matter pathways that link brain regions in each participant. Experts were able to correlate the number of new words learnt by each person during the experiment with a low myelin index, a measure of structure integrity. Results proved that subjects who presented higher myelin concentrations in the structures that carry information to the ventral striatum -- in other words, those that are best connected to the reward area -- were able to learn more words.

"Results provide a neural substrate of the influence that reward and motivation circuitries may have in learning words from context," affirms Josep Marco Pallarès, UB-IDIBELL researcher. The activation of these circuitries during word learning suggests future research lines aimed at stimulating reward regions to improve language learning in patients with linguistic problems.

The fact that non-linguistic subcortical mechanisms, which are much older from an evolutionary perspective, work together with language cortical regions -- which appeared latter -- suggests new language theories trying to explain how reward mechanisms have influenced and supported one of our primal urges: the desire to acquire language and to communicate.

Experiment with words and gambling

Researchers carried out an experiment with thirty-six adults who participated in two magnetic resonance sessions. On the first one, functional magnetic resonance was used to measure participants' brain activity while they perform two different tasks. This technique enables to detect accurately what brain regions are active while a person is performing a certain activity. In the first task, participants must learn the meaning of some new words from context in two different sentences. For instance, subjects saw on a screen the sentences: "Every Sunday the grandmother went to the jedin" and "The man was buried in the jedin." Considering both sentences, participants could learn that the word jedin means "graveyard." Then, participants completed two runs of a standard-event-related money gambling task.

The experiment revealed that when subjects inferred and memorized the meaning of a new word, brain activity in the ventral striatum was increased. Indeed, the same ventral striatum activation was observed when earning money in gambling. Therefore, to learn the meaning of a new word activates reward and motivational circuitries like in gambling activities. Moreover, it was observed that word learning produce an increase of brain activity synchronization between the ventral striatum and cortical language regions.