Razorenova Alexandra M, Chernyshev Boris V, Nikolaeva Anastasia Yu, Butorina Anna V, Prokofyev Andrey O, Tyulenev Nikita B, Stroganova Tatiana A
Center for Neurocognitive Research (MEG Center), Moscow State University of Psychology and Education, Moscow, Russia.
Center for Computational and Data-Intensive Science and Engineering (CDISE), Skolkovo Institute of Science and Technology, Moscow, Russia.
Front Neurosci. 2020 Sep 11;14:895. doi: 10.3389/fnins.2020.00895. eCollection 2020.
Human speech requires that new words are routinely memorized, yet neurocognitive mechanisms of such acquisition of memory remain highly debatable. Major controversy concerns the question whether cortical plasticity related to word learning occurs in neocortical speech-related areas immediately after learning, or neocortical plasticity emerges only on the second day after a prolonged time required for consolidation after learning. The functional spatiotemporal pattern of cortical activity related to such learning also remains largely unknown. In order to address these questions, we examined magnetoencephalographic responses elicited in the cerebral cortex by passive presentations of eight novel pseudowords before and immediately after an operant conditioning task. This associative procedure forced participants to perform an active search for unique meaning of four pseudowords that referred to movements of left and right hands and feet. The other four pseudowords did not require any movement and thus were not associated with any meaning. Familiarization with novel pseudowords led to a bilateral repetition suppression of cortical responses to them; the effect started before or around the uniqueness point and lasted for more than 500 ms. After learning, response amplitude to pseudowords that acquired meaning was greater compared with response amplitude to pseudowords that were not assigned meaning; the effect was significant within 144-362 ms after the uniqueness point, and it was found only in the left hemisphere. Within this time interval, a learning-related selective response initially emerged in cortical areas surrounding the Sylvian fissure: anterior superior temporal sulcus, ventral premotor cortex, the anterior part of intraparietal sulcus and insula. Later within this interval, activation additionally spread to more anterior higher-tier brain regions, and reached the left temporal pole and the triangular part of the left inferior frontal gyrus extending to its orbital part. Altogether, current findings evidence rapid plastic changes in cortical representations of meaningful auditory word-forms occurring almost immediately after learning. Additionally, our results suggest that familiarization resulting from stimulus repetition and semantic acquisition resulting from an active learning procedure have separable effects on cortical activity.
人类语言需要日常记忆新单词，但这种记忆获取的神经认知机制仍极具争议。主要争议在于，与单词学习相关的皮质可塑性是在学习后立即出现在新皮质语言相关区域，还是仅在学习后经过一段长时间巩固所需的第二天才出现新皮质可塑性。与这种学习相关的皮质活动的功能时空模式也基本未知。为了解决这些问题，我们在一项操作性条件任务之前和之后，通过被动呈现八个新的假词，检测了大脑皮质诱发的脑磁图反应。这种关联程序迫使参与者积极寻找四个假词的独特含义，这四个假词分别指代左右手脚的动作。另外四个假词不需要任何动作，因此与任何含义都无关。对新假词的熟悉导致对它们的皮质反应出现双侧重复抑制；这种效应在独特性点之前或左右开始，并持续超过500毫秒。学习后，与未赋予含义的假词相比，对获得含义的假词的反应幅度更大；在独特性点之后144 - 362毫秒内，这种效应显著，且仅在左半球发现。在这个时间间隔内，与学习相关的选择性反应最初出现在颞叶沟周围的皮质区域：颞上沟前部、腹侧运动前皮质、顶内沟前部和脑岛。在此间隔后期，激活进一步扩散到更靠前的高级脑区，并到达左颞极和延伸至眶部的左额下回三角部。总之，目前的研究结果证明，有意义的听觉单词形式的皮质表征在学习后几乎立即发生快速的可塑性变化。此外，我们的结果表明，刺激重复导致的熟悉和主动学习过程导致的语义获取对皮质活动有可分离的影响。
