We all know that you can't teach an old dog new tricks, but what about an old human a new language?
Previous research suggests that it's much easier for young children to pick up a new language than it may be for their parents or even older siblings. A new study offers a solution to jump that evolutionary hurdle.
Using small, imperceptible brain stimulation through the ear, scientists saw improvements in the abilities of adults to recognize foreign language tones compared to those without stimulation. This memory effect lasted even during trials where the stimulation was paused.
This science-fiction inspired brain-hack could help adults overcome their brains' own limitations.
In the study, published Thursday in the journal Science of Learning, the authors explain that part of what has made language acquisition in later life difficult is that the adult brain no longer has the same plasticity — or ability to reshape its synaptic networks to accommodate new information — that it once did in childhood.
"Humans are excellent perceptual learners," the study team writes. "Yet, a notable and well-documented exception is the acquisition of non-native speech categories in adulthood."
However, recent research has found that stimulation to the nervous system paired with behavioral stimuli can result in improved plasticity and memory recall. To test this for language learning, the team designed a small, outer-ear device to non-invasively stimulate a participant's transcutaneous vagus nerve (tVNS) through painless electric pulses.
To test how tVNS might affect the acquisition of language, the researchers recruited a group of 36, native English speaking adults and had them listen to and attempt to identify four different Mandarin tones — a task that can be especially hard for English speakers who are not used to speaking or hearing a tonal language.
Fernando Llanos, a postdoctoral researcher at the University of Pittsburgh's Sound Brain Lab and lead author on the study, says that demonstrating the effectiveness of tVNS in this area could prove beneficial for cognitive learning at large.
"Showing that non-invasive peripheral nerve stimulation can make language learning easier potentially opens the door to improving cognitive performance across a wide range of domains," Llanos explains.
How does it work — Of their 36 participants, the team divided them into groups that received:
- Stimulation while listening to two more difficult Mandarin tones
- Stimulation while listening to two easier Mandarin tones
- Control groups that listened to the tones without stimulation.
All groups were asked to listen and identify which tones they were hearing.
Bharath Chandrasekaran, director of the University of Pittsburg's Sound Lab and co-author of the study, tells Inverse that lessons learned from their test on Mandarian tones could be generalized to other languages as well.
"Mandarin is a great testbed for looking at how specific the stimulation effects are, but we believe that the stimulation effects should generalize to learning sound patterns of other languages," Chandrasekaran says.
The researchers found that participants listening to the easier tones while receiving stimulation outperformed all other groups, being 13 percent better on average at identifying the tones than the other participants and peaked in their ability twice as quickly.
Interestingly, the group listening and identifying the harder tones with stimulation did not show very significant improvement compared to the controls.
"This approach may be leveling the playing field of natural variability in language learning ability."
Matthew Leonard, an assistant professor of neurological surgery at the University of California, San Francisco and co-author of the study, says that the results of this study could level the playing field between adult learners with different language abilities.
"This approach may be leveling the playing field of natural variability in language learning ability," Leonard says. "In general, people tend to get discouraged by how hard language learning can be, but if you could give someone 13 percent to 15 percent better results after their first session, maybe they'd be more likely to want to continue."
The researchers also found that the easy-tones and stimulation test group was able to identify new, easy-tone examples well even without stimulation, suggesting that this approach has a strong potential for being generalizable.
As for what is going on in the brain to make this happen, the researchers hypothesize that it might have something to do with temporarily boosting the attention span over large areas of the brain, making it easier for new stimuli to be processed. More experiments are needed to know for sure.
Following future research studies, Chandrasekaran tells Inverse that a product using this research would likely be available to customers, particularly those suffering from brain damage, within the next two to five years.
"Our next step is to understand the underlying neural mechanism and establish the ideal set of stimulation parameters that could maximize brain plasticity," Chandrasekaran says. "We view tVNS as a potent tool that could enhance rehabilitation in individuals with brain damage."
Abstract: Adults struggle to learn non-native speech contrasts even after years of exposure. While laboratory-based training approaches yield learning, the optimal training conditions for maximizing speech learning in adulthood are currently unknown. Vagus nerve stimulation has been shown to prime adult sensory-perceptual systems towards plasticity in animal models. Precise temporal pairing with auditory stimuli can enhance auditory cortical representations with a high degree of specificity. Here, we examined whether sub-perceptual threshold transcutaneous vagus nerve stimulation (tVNS), paired with non-native speech sounds, enhances speech category learning in adults. Twenty-four native English-speakers were trained to identify non-native Mandarin tone categories. Across two groups, tVNS was paired with the tone categories that were easier- or harder-to-learn. A control group received no stimulation but followed an identical thresholding procedure as the intervention groups. We found that tVNS robustly enhanced speech category learning and retention of correct stimulus-response associations, but only when stimulation was paired with the easier-to-learn categories. This effect emerged rapidly, generalized to new exemplars, and was qualitatively different from the normal individual variability observed in hundreds of learners who have performed in the same task without stimulation. Electroencephalography recorded before and after training indicated no evidence of tVNS-induced changes in the sensory representation of auditory stimuli. These results suggest that paired-tVNS induces a temporally precise neuromodulatory signal that selectively enhances the perception and memory consolidation of perceptually salient categories.