We have long known that language is lateralized to the left hemisphere (LH) in most neurologically healthy adults. In contrast, findings on lateralization of function during development are more complex. As in adults, anatomical, electrophysiological, and neuroimaging studies in infants and children indicate LH lateralization for language. However, in very young children, lesions to either hemisphere are equally likely to result in language deficits, suggesting that language is distributed symmetrically early in life. We address this apparent contradiction by examining patterns of functional MRI (fMRI) language activation in children (ages 4 through 13) and adults (ages 18 through 29). In contrast to previous studies, we focus not on lateralization per se but rather on patterns of left-hemisphere (LH) and right-hemisphere (RH) activation across individual participants over age. Our analyses show significant activation not only in the LH language network but also in their RH homologs in all of the youngest children (ages 4 through 6). The proportion of participants showing significant RH activation decreases over age, with over 60% of adults lacking any significant RH activation. A whole-brain correlation analysis revealed an age-related decrease in language activation only in the RH homolog of Broca’s area. This correlation was independent of task difficulty. We conclude that, while language is left-lateralized throughout life, the RH contribution to language processing is also strong early in life and decreases through childhood. Importantly, this early RH language activation may represent a developmental mechanism for recovery following early LH injury.

我们早就知道，在大多数神经健康的成年人中，语言偏向于左半球（LH）。相比之下，发育过程中功能偏侧化的研究结果更为复杂。与成人一样，婴儿和儿童的解剖学、电生理学和神经影像学研究表明 LH 语言偏侧化。然而，对于年幼的儿童来说，任一半球的损伤同样可能导致语言缺陷，这表明语言在生命早期是对称分布的。我们通过检查儿童（4 至 13 岁）和成人（18 至 29 岁）的功能性 MRI (fMRI) 语言激活模式来解决这一明显的矛盾。与之前的研究相比，我们关注的不是偏侧化本身，而是关注个体参与者随年龄增长的左半球（LH）和右半球（RH）的激活模式。我们的分析表明，所有最小的儿童（4 至 6 岁）的左手语言网络和右手同源语言网络均显着激活。表现出显着 RH 激活的参与者比例随着年龄的增长而下降，超过 60% 的成年人缺乏任何显着 RH 激活。全脑相关分析显示，仅在布罗卡区的 RH 同源体中，语言激活程度与年龄相关。这种相关性与任务难度无关。我们的结论是，虽然语言在整个生命过程中都是左偏化的，但右旋细胞对语言处理的贡献在生命早期也很强，并在童年时期逐渐减弱。重要的是，这种早期的 RH 语言激活可能代表了早期 LH 损伤后恢复的发育机制。