Effect of tDCS over the left inferior parietal lobule region on reading comprehension in a second language (Hebrew)

Reading comprehension is a crucial skill in a globalized world, where a significant portion of communication occurs through written text. Consequently, second-language reading comprehension holds substantial importance. Studies have found that traditional reading models can be adapted to explain second-language reading comprehension processes, particularly among unskilled readers, who rely on the sub-lexical pathway. This pathway, which operates based on grapheme-to-phoneme conversion to extract meaning from words, is inherently slower and primarily used by novice readers. Neuroimaging studies that have identified brain regions involved in sub-lexical reading processes have pointed to the Inferior Parietal Lobule (IPL) as a key region in integrating phonological and orthographic processing. More broadly, research has found that second-language acquisition is associated with increased gray matter density in the IPL, and that this increase correlates with second-language proficiency. Another critical factor influencing reading comprehension—especially in a foreign language—is working memory (WM). Working memory refers to the ability to maintain information in an accessible state for short periods (seconds to minutes). Due to the inherent challenges of reading in a second language, particularly among low-proficiency individuals, working memory plays a decisive role in second-language reading comprehension. Several studies have identified the IPL—specifically Brodmann area (BA) 40—as a neural correlate of the phonological store, consistent with research linking the IPL to second-language phonological processing. In recent years, non-invasive brain stimulation techniques have gained increasing attention for their ability to influence brain activity and cognitive abilities. One such technique, transcranial direct current stimulation (tDCS), involves the application of a weak electrical current (1–2 mA) via electrodes placed on the scalp, aiming to modulate neural activity in a targeted brain region. Flöel’s (2008) pioneering research demonstrated that tDCS can enhance linguistic abilities, and subsequent studies have shown that electrical stimulation may improve first-language skills such as reading comprehension.

This study aims to expand existing knowledge on the effects of tDCS on second-language proficiency. Specifically, we examined the impact of brain stimulation on English reading comprehension among native Hebrew speakers, targeting the left IPL. Since working memory plays a crucial role in second-language reading comprehension and the IPL is associated with both working memory and phonological processing, we hypothesized that participants with lower working memory capacity would experience the most significant improvements following brain stimulation. The study included 47 healthy participants (ages 18–49, M = 21.51, SD = 7.077), all native Hebrew speakers, who were assigned to an experimental or control group. Participants underwent a working memory assessment (Digit Span test), an English proficiency test (CEFR, 2001) and an English reading comprehension test. The experimental group received active stimulation (1.5 mA, anodal electrode at BA 39, cathodal electrode at BA 10) for 20 minutes, whereas the control group received sham stimulation. Following the stimulation, all participants completed a parallel English reading comprehension test. The results indicated that participants with low working memory capacity (scores below 27) significantly improved their reading comprehension performance following stimulation (F(1,43) = 5.5, p = .02). In contrast, participants with high working memory capacity (scores of 27 or higher) exhibited a significant decline in reading comprehension after stimulation (F(1,43) = 5.1, p = .03). These findings confirm the hypothesized relationship between IPL activity and second-language reading comprehension and further highlight the critical role of working memory in this process. However, the decline in performance among high working memory individuals underscores the need for caution when using tDCS to enhance linguistic skills. Future research is required to explore the effects of tDCS on different populations and linguistic abiliti.