The brain systems for language learning predate both language and humans
Why has the human brain proved adept at learning languages? One explanation is that we learn language in specially dedicated areas of the brain, but new research from Georgetown University Medical Centre seems to rule this out. In fact, language is learned in areas of the brain that not only emerged before language – they predate humans, too.
Interestingly, the two brain circuits in question – declarative and procedural memory – seem to process different elements of the lingual puzzle at different ages. Declarative memory seems to deal with the raw recall of words in a language – and it’s the same part that you would use to memorise a shopping list, someone’s face or recall the plot of a TV box set.
Procedural memory, on the other hand, is usually connected to learning physical tasks like driving, riding a bike or playing a musical instrument. The grammatical abilities of children learning their native tongue correlated strongly with this kind of memory, but for adults learning a second language, it was a mixture of declarative and procedural – the former for early stages, and the latter further along the line.
“The two brain systems, declarative and procedural memory, exist in animals as well as humans, and thus are evolutionarily ancient,” Michael T. Ullman, professor of neuroscience at Georgetown University, and senior investigator on the study tells me via email. “In particular, they are found across mammals, and (in different forms) in other vertebrates as well. Hence they predate humans by a long time.”
According to Ullman, these structures likely carry out many functions across species. A bird’s declarative memory may be where a bird remembers where it put some acorns, for example, while a rat’s procedural memory might be in charge of recalling grooming sequences. For Ullman, these functions echo their belated use in humans rather neatly.
“These functions are almost eerily reminiscent of the role of these two systems in language,” he explains. What a given word means, he points out, is “largely arbitrary, unpredictable, just as where the bird might have put the acorns is largely arbitrary, and just has to be remembered.” Meanwhile, grammar is a series of rule-governed actions – like the rats’ grooming sequences.
“In addition, in modern scientific experiments, both systems have been shown to be important for navigation,” he adds. “The hippocampal declarative memory based system for navigating via landmarks (which are arbitrary), and the striatum/basal ganglia based procedural memory for navigating by learning to turn at particular points in a sequence.”
The researchers reached their conclusions by studying 16 studies across 665 participants, multiple languages and tasks encompassing reading, listening and speaking tests. The researchers believe this approach is preferable to brain imaging studies, because both systems may be involved in non-learning functions. “In neuroimaging studies two functions can lead to activation of the same regions even if they depend on distinct neural correlates at a more fine-grained level,” the paper explains. “For example, the role of basal ganglia in grammar may in part be due to its role in attention and working memory as well as its role in procedural memory.”
The next steps
In any case, the study points researchers in a number of useful directions. The first is to examine the role of the genes associated with the two brain circuits. On a related note, the evolution of the brain systems could give us new insights into how language has evolved.
But more practically, for now, the findings could improve the way we learn foreign languages, and perhaps help with language problems in disorders. For the latter, pharmaceutical solutions (e.g: memantine) and behavioural strategies (e.g: spacing out the presentation of information) have been shown to boost learning and retention in the highlighted brain systems.
“The bottom line is that the research suggests that pharmacological or behavioral (or other) techniques that have been shown to improve learning and retention in the memory systems may be expected to also work for language learning,” Ullman says. “Both for second/foreign language learning and in language disorders such as autism, dyslexia, or aphasia.”
The research will be published in PNAS.