Аннотация:It is generally accepted that language acquisition involves biological mechanisms of associative learning. Particularly, it has been proposed that meaning of action words is acquired as a result of co-activation of cortical areas supporting both speech processing and motor control. If true, such learnt audio-motor neural representations can be retrieved reciprocally, i.e., auditory signal induces the recall of its motor associate, or the other way around. This view suggests that after the concurrent presence of a movement and its auditory associate, as is the case of action word learning, preparation of motor response should automatically activate auditory word representation in the left temporal cortex.
On order to test this intriguing prediction, we used MEG recording during a novel auditory-motor learning procedure. Participants were required to discover novel action words meaning from an association between their movements and pseudowords by way of trial-and-error learning. We explored the magnetic counterpart of motor readiness potential (mMRP), which precedes motor response in a phase-locked manner presumably reflecting motor initiation and planning. Sources of mMRP were reconstructed using MNE software. We expected that as a result of successful auditory-motor mapping, the mMRP would comprise a stronger auditory component at the advanced stage of auditory-motor association learning as compared to initial trials.
Our results revealed that, as expected, apart from classical higher-tier motor regions, the motor response initiation activated the auditory speech areas of temporal cortex as learning proceeded. The auditory activation was phase-locked to movement onset, and lasted from -500 to -150 ms relative to an overt motor response. The learning-related response was found predominantly in the left hemisphere and involved a widespread network of temporal cortical areas linked to auditory speech processing: STG/STS/MTG, temporal pole, posterior insula, and an area at the parietotemporal boundary.
Our finding is consistent with human and nonhuman primate studies showing cross-modal activation of neurons in the auditory association cortex in response to stimuli of other modalities. The activation of speech areas synchronously with its paired motor associates suggests that the memory for actions is stored in distributed cortical representations including those for related action words.