18Whether short-term learning of new words can induce rapid changes in cortical areas involved in 19 distributed neural representation of the lexicon is a hotly debated topic. To answer this question, 20 we examined magnetoencephalographic phase-locked responses elicited in the cerebral cortex by 21 passive presentation of eight novel pseudowords before and immediately after an operant 22 conditioning task. This procedure forced participants to perform an active search for unique 23 meaning of four word-forms that referred to movements of their own body parts. While 24 familiarization with novel word-forms led to bilateral repetition suppression of cortical responses 25 to all eight pseudowords, these reduced responses became more selectively tuned towards newly 26 learned action words in the left hemisphere. Our results suggest that stimulus repetition and active 27 learning of semantic association have separable effects on cortical activity. They also evidence 28 rapid plastic changes in cortical representations of meaningful auditory word-forms after active 29 learning. 30 Keywords 31 associative learning, word semantics, MEG, repetition suppression, cortical plasticity, 32 familiarization.33 Cortical plasticity induced by active learning of novel words 3 2017) explored efficacy of associative learning in comparison with statistical learning when the 113 participants learned four tri-syllabic pseudowords presented within a continuous stream of auditory 114 consonant-vowel (CV) syllables. The results showed that during the learning phase, the "semantic" 115 N400 component of the ERP (Kutas & Federmeier, 2011) is elicited by pseudowords associated 116 with visual images but not by pseudowords detected solely on the probability of transitions 117between syllables embedded into a continuous auditory stream. However, these ERP findings did 118 not provide evidence for the "fast mapping" hypothesis. Indeed, since the participants were 119 required to listen carefully to the auditory stream with the task of discovering new words, learning-120 related enhancement of N400 might have been elicited by an on-line attentional modulation, i.e., 121 attention biased toward auditory word-forms associated with pictures during the learning session. 122 Cortical plasticity induced by active learning of novel words 6To prove semantic cortical plasticity, enhanced N400 should be observed during passive exposure 123 to the newly learned word-forms. 124In summary, the current picture of "fast mapping" in word learning is obviously far from 125 complete. It is a controversial topic with a body of associated literature, yet the mere existence of 126 "fast mapping" in forming cortical representations of word semantics is still considered doubtful 127 by many (see Cooper, Greve, Henson, Greve, & Henson, 2018 for review). One of the reasons for 128 this skepticism might be the passive nature of the learning procedure used in the previous 129 experiments. A word, which is learned passively through repetition or instructions, is t...