Electrical Brain Stimulation Helps Memorise New Words
A team of researchers at HSE University, in collaboration with scientists from Russian and foreign universities, has investigated the impact of electrical brain stimulation on learning new words. The experiment shows that direct current stimulation of language centres—Broca's and Wernicke's areas—can improve and speed up the memorisation of new words. The findings have been published in Neurobiology of Learning and Memory.
The transcranial direct current stimulation (tDCS) technique involves applying a low direct current to specific areas of the brain. The advantages of tDCS include its simplicity, affordability, and non-invasive nature, meaning it does not require surgical intervention or expensive equipment. All that is required is the correct placement of electrodes on the head.
Researchers from HSE University, the N.P. Bekhtereva Institute of the Human Brain of the Russian Academy of Sciences, Sirius University, and the Gestalt Centre London, in collaboration with St Petersburg State University, investigated how transcranial direct current stimulation of Broca's and Wernicke's areas affects new word acquisition. These two areas are the brain's primary language centres, typically located in the left hemisphere for most people. The authors of the study conducted a large-scale, complex experiment involving 160 participants.
'We developed a rather complex experimental design, aiming to account for as many factors influencing learning as possible to obtain the most comprehensive picture of the process of acquiring new words. We aimed to determine whether transcranial direct current stimulation actually aids in memorising new words, whether a specific stimulation mode influences memorisation, and which brain area—Broca's or Wernicke's—plays a more significant role in the process of learning new words,' explains Olga Sherbakova, Leading Research Fellow at the Cognitive Health and Intelligence Centre of the HSE Institute for Cognitive Neuroscience.
To account for all these factors, participants were randomly assigned to five groups, subjected, respectively, to anodal stimulation of Broca’s area, anodal stimulation of Wernicke’s area, cathodal stimulation of Broca’s area, cathodal stimulation of Wernicke’s area, and placebo stimulation as a control, with inactive electrodes placed on the scalp.
The stimulation lasted 15 minutes, after which participants were instructed to memorise 16 new words—or more precisely, pseudowords—designed specifically for the experiment using the phonetic and rhythmic structure of the Russian language.
'People use two strategies to learn new words: explicit learning, where we are shown an object and told, "this is a table," and implicit learning, where we infer the meaning of a word from its context. In our experiment, we aimed to determine which memorisation strategy would be more effective under stimulation,' Shcherbakova explains. 'Additionally, we asked the participants to repeat some words aloud to investigate whether, as is commonly believed, articulation—pronouncing memorised words aloud—actually aids in memorisation.'
During the experiment, participants were shown images of unfamiliar objects, such as ancient musical instruments or rare deep-sea fish. While viewing each image, participants either heard a new word, such as 'This is SEN' (explicit strategy), or a question, such as 'Is SEN furry?' (implicit strategy).
After the learning phase, each group was assessed to determine which of them learned the new words most effectively and whether the learning strategy had any impact on the outcome. Participants first had to recognise a word by ear and then associate it with the image. The outcome assessment considered both the speed and accuracy of the response.
The results of the experiment show that both the explicit and implicit strategies lead to similarly successful word acquisition but engage different neural mechanisms, as evidenced by the varying effects of the different stimulation modes. It was also found that articulation contributes to better memorisation: participants recognised the words they had said aloud during the learning phase more accurately and quickly.
Most importantly, the study authors demonstrated that transcranial direct current stimulation significantly improves word memorisation, with the greatest effect resulting from anodal stimulation of Broca's area and cathodal stimulation of Wernicke's area. It is also important to note that the study found no adverse effects of tDCS on the outcomes of word learning in any of the groups.
This is the first tDCS study to consider such a wide range of factors potentially affecting language learning and to yield reliable results. 'We were able not only to demonstrate that tDCS has a positive effect on language learning, but also to identify the optimal stimulation modes for such learning,' Sherbakova emphasises.
In the future, the researchers plan to investigate the delayed effects of tDCS and determine how long its positive impact on the brain's language areas lasts. Potentially, transcranial direct current stimulation could be used to restore language abilities in patients after a stroke, brain injury, or neurodegenerative disease, as well as to enhance the cognitive abilities of healthy individuals.