Enhanced activations in the dorsal inferior frontal gyrus specifying the who, when, and what for successful building of sentence structures in a new language.

It has been argued that the principles constraining first language acquisition also constrain second language acquisition; however, neuroscientific evidence for this is scant, and even less for third and subsequent languages. We conducted fMRI experiments to evaluate this claim by focusing on the building of complex sentence structures in Kazakh, a new language for participants having acquired at least two languages. The participants performed grammaticality judgment and subject-verb matching tasks with spoken sentences. We divided the participants into two groups based on the performance levels attained in one of the experimental tasks: High in Group I and Low in Group II. A direct comparison of the two groups, which examined those participants who parsed the structures, indicated significantly stronger activations for Group I in the dorsal left inferior frontal gyrus (L. IFG). Focusing on Group I, we tested the contrast between the initial and final phases in our testing, which examined when the structures were parsed, as well as the contrast which examined what structures were parsed. These analyses further demonstrated focal activations in the dorsal L. IFG alone. Among the individual participants, stronger activation in the dorsal L. IFG, measured during the sentence presentations, predicted higher accuracy rates and shorter response times for executing the tasks that followed. These results cannot be explained by task difficulty or memory loads, and they, instead, indicate a critical and consistent role of the dorsal L. IFG during the initial to intermediate stages of grammar acquisition in a new target language. Such functional specificity of the dorsal L. IFG provides neuroscientific evidence consistent with the claims made by the Cumulative-Enhancement model in investigating language acquisition beyond target second and third languages.

Differential networks for processing structural dependencies in human language: linguistic capacity vs. memory-based ordering.

Surface linear (left-to-right) arrangements of human languages are actually an amalgam of the core language system and systems that are not inherently related to language. It has been widely recognized that an unbounded array of hierarchically structured linguistic expressions is generated by the simplest combinatorial operation "Merge," and the notion of Merge-generability has been proposed as a key feature that characterizes structural dependencies among linguistic elements. Here we tested Merge-generable dependencies by using a Subject-Predicate matching task, which required both linguistic capacity and short-term memory. We used three types of dependency: Nesting, Crossing, and Grouping as the control. The Nesting dependency is totally Merge-generable, while the Crossing dependency requires some additional processes for memory-based ordering. In order to identify the regions employed for these two dependencies, we directly compared cortical responses to the sentence stimuli (with noun phrases and an adverb as the first half of stimuli, and with verbs as the latter) using functional magnetic resonance imaging (fMRI), and the following results were obtained. First, for the Nesting - Crossing contrast, significant activations were observed in the bilateral lateral premotor cortices (LPMCs) and inferior frontal gyri, left middle temporal gyrus, and bilateral angular/supramarginal gyri, indicating engagement of the syntax-related networks. In contrast, the Crossing - Nesting contrast showed focal activations in the left fusiform gyrus, lingual gyrus, and middle occipital gyrus (L. FG/LG/MOG). Secondly, for the first half of the Nesting stimuli, signal changes in the bilateral LPMCs were well fitted with the estimates of computational costs to search the workspace and to select items (Σ operations). Moreover, for the latter half of the Crossing stimuli, the signal changes in the L. FG/LG/MOG were differentially fitted with the estimates of loads related to the ordering of elements/words (numbers of Ordering). Thirdly, these fitting models were by far more likely than the exchanged estimates between bilateral LPMCs and L. FG/LG/MOG, confirming a double dissociation for primary processes with Σ and Ordering. In conclusion, these results indicate that separate cortical networks are differentially employed, and their careful elucidation will provide further insights and challenges.

Paper Notebooks vs. Mobile Devices: Brain Activation Differences During Memory Retrieval.

It remains to be determined how different inputs for memory-encoding, such as the use of paper notebooks or mobile devices, affect retrieval processes. We compared three groups of participants who read dialogues on personal schedules and wrote down the scheduled appointments on a calendar using a paper notebook (Note), an electronic tablet (Tablet), or a smartphone (Phone). After the retention period for an hour including an interference task, we tested recognition memory of those appointments with visually presented questions in a retrieval task, while scanned with functional magnetic resonance imaging. We obtained three major results. First, the duration of writing down schedules was significantly shorter for the Note group than the Tablet and Phone groups, and accuracy was much higher for the Note group in easier (i.e., more straightforward) questions. Because the input methods were equated as much as possible between the Note and Tablet groups, these results indicate that the cognitive processes for the Note group were deeper and more solid. Second, brain activations for all participants during the retrieval phase were localized in the bilateral hippocampus, precuneus, visual cortices, and language-related frontal regions, confirming the involvement of verbalized memory retrieval processes for appointments. Third, activations in these regions were significantly higher for the Note group than those for the Tablet and Phone groups. These enhanced activations for the Note group could not be explained by general cognitive loads or task difficulty, because overall task performances were similar among the groups. The significant superiority in both accuracy and activations for the Note group suggested that the use of a paper notebook promoted the acquisition of rich encoding information and/or spatial information of real papers and that this information could be utilized as effective retrieval clues, leading to higher activations in these specific regions.

Enhanced activations in syntax-related regions for multilinguals while acquiring a new language.

The neuroscientific foundation of multilingualism, a unique cognitive capacity, necessitates further elucidation. We conducted an fMRI experiment to evaluate the acquisition of syntactic features in a new language (Kazakh) for multilinguals and bilinguals. Results showed that the multilinguals who were more proficient in their second/third languages needed fewer task trials to acquire Kazakh phonology. Regarding group differences, the reduction in response times during the initial exposure to Kazakh were significantly larger for the multilinguals than the bilinguals. For the multilinguals, activations in the bilateral frontal/temporal regions were maintained at a higher level than the initial level during subsequent new grammar conditions. For the bilinguals, activations in the basal ganglia/thalamus and cerebellum decreased to the initial level each time. Direct group comparisons showed significantly enhanced activations for the multilinguals in the left ventral inferior frontal gyrus. These results indicate that both syntax-related and domain-general brain networks were more enhanced for the multilinguals. We also unexpectedly observed significant activations in the visual areas for the multilinguals, implying the use of visual representation even when listening to speech sounds alone. Because the multilinguals were able to successfully utilize acquired knowledge in an accumulated manner, the results support the cumulative-enhancement model of language acquisition.

[Multilingualism and the Development of the Brain].

Multilingualism is merely a parametric variation in the faculty of natural language, and it is possible to simultaneously acquire multiple languages, including dialects, at any age. While acquisition of a native language, which occurs in synchrony with development of the brain, is a multiple-step process, second language acquisition is continuous. Here, we introduce the Cumulative-Enhancement model, which states that acquisition of one additional language is beneficial for the subsequent acquisition of another. We further discuss how syntax-related networks, including multiple language areas in the brain, become functional during the course of language acquisition.

[The Brain, the Source of Multilingualism].

Multiple languages can be used at command, if those language abilities were acquired in childhood. In this article, we report the possibility that such abilities are retained throughout adulthood for linguistic savants. We focus on Emil Krebs, a speaker of dozens of languages, and argue about the vast capacity of the multilingual brain. Moreover, we introduce the asymmetry of the grammar center and brain activation changes due to linguistic proficiency, both of which are findings from research on the second language acquisition capability of the brain. It is plausible that research on multilingualism will shed light on the mystery of human creativity in fine arts.