ИСТИНА

It is generally accepted that meaning of action words is acquired as a result of co-activation of cortical areas supporting both speech processing and motor control. However, action word learning in the natural environment assumes a temporal gap between an action and its word associate, and how the brain achieves a precise temporal coupling of auditory and motor cortical representations is largely unknown. We hypothesized that in the course of association learning such coherent auditory-motor neural representations might gradually emerge due to strengthening of the reciprocal inter-modal connections. Through activation spreading from motor areas to speech-related areas, preparation of motor response triggered by a specific pseudoword could repeatedly activate auditory word representation in the left temporal cortex. In order to test this intriguing prediction, we recorded MEG in 28 adult subjects who were involved in a novel auditory-motor learning procedure. The participants were required to discover meaning of four novel action words from their association with the specific actions by way of “trial-and-error” learning in the presence of four interfering pseudowords. We explored the magnetic counterpart of motor readiness potential, which precedes motor response in a phase-locked manner presumably reflecting motor initiation and planning. Cortical sources of response-locked magnetic field were reconstructed using MNE software. We found that in the course of auditory-motor learning, the motor readiness magnetic field gradually started to be associated with response-locked activation in the perisylvian speech-related areas. This perisylvian activation was virtually absent for actions performed in the initial learning trials (before associative learning was established), and its strength significantly increased as learning proceeded. The difference between learnt and naïve trials occurred in the event-related fields preceding the motor response onset by 150 - 500 ms, and it was clearly time-locked to the movement onset rather than to the stimulus onset. Perisylvian activation correlated with shortening of the behavioral response time during learning acquisition: the stronger was this brain signal, the shorter was response time in the end of the learning sessions in relation to the beginning of the learning sessions. Thus, action preparation recurrently re-activates speech processing thus guaranteeing activation of the auditory and motor nodes of emerging network to be tightly time-synchronized. Our results demonstrate for the first time that experimentally induced association between acoustically presented pseudowords and actions involves activation of speech-related cortical areas during action planning and initiation. Presumably, newly formed auditory-motor attractor neural networks induce such a recurrent reactivation of phonological and lexical circuits, thus likely promoting further increase in the strength and specificity of the association between newly learned pseudowords and corresponding actions.