Online build-up of neocortical memory traces for spoken words is facilitated by novel semantic associations: MEG data

Recent research has shown that the brain is capable of a rapid build-up of novel cortical memory traces for words during mere perceptual exposure to new lexical items. This has been shown as an online (within minutes) increase in the amplitude of electrophysiological responses to new word forms even when they have no specific meaning attached and are not attended to or actively rehearsed by the learners. However, the operation of this fast cortical language-learning mechanism in online acquisition of word meaning has not been sufficiently investigated yet. To address immediate plasticity caused by rapid learning of new words, we presented our participants with novel word forms in a word-learning task taking place during a short (10 minutes, 20 presentations of each item) magnetoencephalography (MEG) recording session. Novel word forms were either learned perceptually through auditory exposure only or were assigned a clear semantic reference using a word-picture association task, in which they were presented in conjunction with images of novel objects. Real familiar words were used as control stimuli. MEG responses were scrutinized as a moving average of three trials for each stimulus type (i.e. real words, perceptually learned novel word forms and semantically learned novel word forms). The results show that, already after approximately five presentations of each stimulus, novel stimuli learnt through semantic association demonstrated stronger activation over the left perisylvian cortices than perceptually acquired word forms that lacked semantic reference. Perceptual items also demonstrated a linear learning-related amplitude increase, but at a much slower pace, spread across the 10-minute recording session. This result suggests a more efficient process of online novel word memory trace build-up in the presence of semantic reference. This could be due to more widespread concurrent brain activations resulting in a more robust associative learning ultimately creating novel memory circuits. Our results confirm rapid formation of memory traces for novel words over a course of a short exposure and suggest facilitatory effects of acquisition of novel semantics on the neocortical memory trace formation.