Language learning in the adult brain: disrupting the dorsolateral prefrontal cortex facilitates word-form learning
"The results support the hypothesis that a mature prefrontal cortex competes with implicit learning of word-forms. The findings provide new insight into the competition between brain mechanisms that contribute to language learning in the adult brain."
Introduction
It is well known that children surpass adults in their language learning ability, in particular for certain aspects of language that involve grammar and phonology1,2, but it has remained unclear why this is the case3,4. Adults outperform children in most measures of cognition, especially those that rely on the prefrontal cortex that maturates until adulthood, such as executive functions, attention and working memory5. Yet, they fail learning languages with the ease that children do. It has been proposed that the mature brain systems supporting these cognitive functions interfere with implicit procedural learning, which contributes to certain aspects of language learning such as word-forms or grammar6,7,8,9. However, there is little experimental evidence supporting this hypothesis.
Multiple brain systems support learning in cooperative and sometimes competitive ways10,11. For example, procedural and declarative memory systems are known to interact during learning12. The declarative memory system is characterized by voluntary processes that rely on attentional resources mediated by prefrontal and medial-temporal lobe structures. Procedural memory on the other hand is part of implicit memory. Learning in implicit memory takes place without the intention to do so, and so whereby awareness of the process or the outcome is not needed for learning to occur13,14. Procedural memory relies on such learning allowing the acquisition of a sequence through repeated exposure...
Overall, our findings are in line with previous studies demonstrating that reducing the reliance on the prefrontal cortex can improve task performance...
Procedural memory is thought to be important for certain aspects of language learning, such as grammar and word-forms, while other more idiosyncratic aspects, such as associating semantics with phonology, rely more on an explicit declarative memory system. In a recent study, Finn and colleagues demonstrated that adults’ cognitive functions that involve attention and effort interact with specific language-learning processes6. For instance, directing effort or attentional control toward the phonological input benefits word-segmentation but disrupts learning phonological categories of a novel word-form structure. The authors argued that competition from executive functions, such as effort or the allocation of attention that support a late-developing declarative memory system, can explain why adults have difficulties in some but not all aspects of language learning compared to children, especially in the aspects that are related to procedural memory....
Together with earlier studies on motor learning, the current results support the idea that different memory systems compete during automatic skill learning..."
https://www.nature.com/articles/s41598-017-14547-x
