Abstract
AbstractResearch on the effects of bi- and multi-lingualism on brain structure has so far yielded variable patterns. Although it cannot be disputed that learning and using additional languages restructures grey (cortical, subcortical and cerebellar) and white matter in the brain, both increases and reductions in regional volume and diffusivity have been reported. This paper revisits the available evidence from simultaneous and sequential bilinguals, multilinguals, interpreters, bimodal bilinguals, children, patients and healthy older adults from the perspective of experience-based neuroplasticity. The Dynamic Restructuring Model (DRM) is then presented: a three-stage model accounting for, and reinterpreting, all the available evidence by proposing a time-course for the reported structural adaptations, and by suggesting that these adaptations are dynamic and depend on the quantity and quality of the language learning and switching experience. This is followed by suggestions for future directions for the emerging field of bilingualism-induced neuroplasticity.
Highlights
Experience-dependent brain plasticityResearch in the past 20 years has convincingly demonstrated that the structure of the human brain is far from static
Beyond natural maturational processes, such as cortical thinning and increases in myelination (Muftuler, Davis, Buss, Solodkin, Su, Head, Hasso & Sandman, 2012; Tamnes, Østby, Fjell, Westlye, Due-Tønnessen & Walhovd, 2010), it is well documented that the acquisition and usage of a new skill can be accompanied by structural adaptations in brain regions that subserve that particular skill
Learning to juggle induces rapid changes in both grey and white matter structure in motor and visual regions of the cortex (Draganski, Gaser, Busch, Schuierer, Bogdahn & May, 2004; Scholz, Klein, Behrens & Johansen-berg, 2010), and professional basketball players have been documented to have increased volume in a wide network of cortical regions (Tan, Pi, Wang, Li, Zhang, Dai, Zhu, Ni, Zhang & Wu, 2017), while it has been shown that learning a complex balancing task causes grey matter adaptations which are later followed by white matter adaptations (Taubert, Draganski, Anwander, Muller, Horstmann, Villringer & Ragert, 2010)
Summary
Research in the past 20 years has convincingly demonstrated that the structure of the human brain is far from static. Related to tool use throughout the training, and especially at the initial stages; interestingly, after the end of the training the same regions started showing a DECREASE in volume (which did not reach baseline levels), but without the loss of the skill In other words, it appears that cortical volumetric increase was only one step in the process of learning and consolidating a new skill. Based on this and similar findings (e.g., Reed, Riley, Carraway, Carrasco, Perez, Jakkamsetti & Kilgard, 2011), Lövdén, Wenger, Mårtensson, Lindenberger and Bäckman (2013) proposed the expansion-partial renormalization hypothesis (EPH) According to this approach, learning of a skill leads to local generation of new dendritic spines in the region that undertakes the skill learning, which in turn provide an increased number of neural pathways compared to pre-training. The reported changes in diffusivity are subject to the individual’s experience and can be assumed to depend on, and to regulate, the velocities of impulse conductions (Zatorre, Fields & Johansen-Berg, 2013)
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