The timing of language learning shapes brain structure associated with articulation

Abstract

We compared the brain structure of highly proficient simultaneous (two languages from birth) and sequential (second language after age 5) bilinguals, who differed only in their degree of native-like accent, to determine how the brain develops when a skill is acquired from birth versus later in life. For the simultaneous bilinguals, gray matter density was increased in the left putamen, as well as in the left posterior insula, right dorsolateral prefrontal cortex, and left and right occipital cortex. For the sequential bilinguals, gray matter density was increased in the bilateral premotor cortex. Sequential bilinguals with better accents also showed greater gray matter density in the left putamen, and in several additional brain regions important for sensorimotor integration and speech-motor control. Our findings suggest that second language learning results in enhanced brain structure of specific brain areas, which depends on whether two languages are learned simultaneously or sequentially, and on the extent to which native-like proficiency is acquired.

Age of acquisition impacts the brain differently depending on neuroanatomical metric

“…Whole‐brain analyses were conducted on 334 brain scans using general linear modeling to determine differences in brain structure relative to AoA. Because previous studies have found neuroanatomical effects associated with AoA by conducting analyses that treat AoA as categorical (i.e., Berken et al, ; Kaiser et al, ; Klein et al, ; Mohades et al, 2012) and continuous (i.e., Klein et al, ; Nichols & Joanisse, ; Wei et al, ), this study used both group comparisons (ANOVA) and regression analyses (in which AoA was treated as a continuous variable). Analyses of cortical thickness, volume, and density were conducted.…”

“…Whole-brain analyses were conducted on 334 brain scans using general linear modeling to determine differences in brain structure Berken et al, 2016b;Kaiser et al, 2015;Klein et al, 2014;Mohades et al, 2012) and continuous (i.e., Klein et al, 2014;Nichols & Joanisse, 2016;Wei et al, 2015), this study used both group comparisons (ANOVA) and regression analyses (in which…”

“…Based on the sensorimotor hypothesis (Hernandez & Li, 2007), one could surmise that the later an individual begins learning a second language, the more likely it is that structures involved in higher-level cognition (e.g., dorsolateral prefrontal cortex [DLPFC] and parietal regions) will be recruited to support the L2, as opposed to sensorimotor areas such as the basal ganglia. For instance, Berken et al (2016b) found that GM density was greater in simultaneous compared to sequential bilinguals in areas related to articulation, such as the left putamen, prefrontal, insular, and occipital cortices, whereas sequential bilinguals had greater GM density in the bilateral premotor cortex. Furthermore, the sequential bilinguals with more native-like accent showed greater GM density in the left premotor cortex, left inferior frontal gyrus (IFG), right primary motor cortex, right Heschl's gyrus, right lateral occipital cortex (LOC), right cerebellar vermis, and bilateral IPL.…”

Transcending as a driver of development

“…Cortical thickness begins to decrease at the rate of 1–2% each year, beginning around 10 years of age . The connections between the rest of the brain and the prefrontal cortex—the core executive centers—begin to myelinate at 12 years of age and continue throughout this period . By middle to late adolescence, teenagers have fewer connections than they did as children, but these connections are selectively stronger within specific brain networks.…”

“…4 The connections between the rest of the brain and the prefrontal cortex-the core executive centersbegin to myelinate at 12 years of age and continue throughout this period. 31 By middle to late adolescence, teenagers have fewer connections than they did as children, but these connections are selectively stronger within specific brain networks. This period is marked by the maturation of two competing systems: the low-road emotional system, including the amygdala and nucleus accumbens, and the high-road executive system, including the prefrontal cortex and bilateral parietofrontal network.…”