Poster B32, Tuesday, August 20, 2019, 3:15 – 5:00 pm, Restaurant Hall
Online build-up of cortical representations for novel morphemes and words: multi-modal evidence of ultra-rapid functional and structural plasticity in language acquisition
Yury Shtyrov1,2;1Aarhus University, 2St. Petersburg University
Humans learn new language elements rapidly, an essential skill which ensures high efficiency of our communication system. However, the neural bases of this important function are poorly understood. How exactly are words, morphemes and their combinations acquired by our brain, and can we track this process neurophysiologically? To this end, we ran a series of multi-modal neuroimaging studies using electrophysiological, structural and neurostimulational techniques to address the online acquisition processes. We employed electro- and magnetoencephalography (EEG, MEG) to register ERP/ERF indices of (1) long-term memory trace activation, visible in the form of enhanced responses to familiar (i.e. successfully acquired) morphemes, and (2) connections between morphemic representations, manifest as priming effects leading to response reduction. Using this approach, we addressed the brain mechanisms of online learning of new language representations for monomorphemic meaningless wordforms, new meaningful words as well as novel affixes in the native or second languages. Furthermore, to tackle the causal role of the neurophysiological processes at hand, we used brain stimulation methods – transcranial magnetic stimulation (TMS) and transcranial direct current stimulation (tDCS) – to interfere with the cortical function in the learning process both at the core language systems level (Broca and Wernicke areas) and in the domain of referential semantics (modality-specific areas). Finally, we used novel structural MRI methods (diffusion kurtosis imaging, DKI) to understand the microstructural changes underpinning language learning in the brain. We find that the temporal and inferior-frontal areas of the neocortex exhibit complex changes in activation patterns in in the process of acquiring novel linguistic representations. These become exhibited as both an increase in activation for novel representations, and a decrease of response amplitudes for morphologically primed elements. These effects are (1) manifest almost immediately, within mere minute of exposure, (2) to a substantial degree independent of attention, reflecting a largely automatic nature of initial word acquisition stages, (3) most efficient for native language, (4) present both immediately and after an overnight consolidation, and (5) operate in both visual and auditory modalities. By using neurostimulation techniques to interfere with modality-specific systems in the process of learning, we could show their role in the acquisition of semantics (e.g. motor cortex for action-relation words). Modulating activity in the core language cortices with tDCS changes the balance between the acquisition of concrete and abstract language and may help promote more successful learning. Finally, our experiments with microimaging DKI methodology suggest that rapid plastic changes in a range of cortical areas (including ATL and hippocampus) take place within even a short naturalistic language learning session. These experiments show that our brain is capable of a rapid formation of new cortical circuits online, as it gets exposed to novel linguistic patterns in the input. They demonstrate that the use of a comprehensive combination of neuroimaging tools to address function, structure, dynamics and causal relationships may provide the best window on the dynamic processes of neural memory-trace build-up and activation.
Themes: Meaning: Lexical Semantics, Multilingualism
Method: Other