Continuous Theta-Burst Stimulation of the Primary Motor Cortex Induces Specific Influence on Novel Vocabulary Acquisition in Different Learning Environments

Abstract

The primary motor cortex takes part in various stages of language learning accompanied by human motor activity. However, previous studies of causal relationships between the activation of primary motor cortex and efficiency of language tasks reveal contradictory results, likely due to diverging learning environments and specific movement patterns required by different experimental designs. The goal of this research was to comprehensively investigate the effect of continuous theta-burst magnetic stimulation (cTBS) of the primary motor cortex on the acquisition of new words while modulating the learning environment and the motor response during the learning process. Following cTBS of the primary motor cortex or control conditions (sham and active control cTBS), the subjects (n = 96) completed a novel word learning task, which involved associating visually presented objects with spoken word forms using a virtual reality (VR) or conventional computer monitor environment. In each environment, the subjects were exposed to eight novel words embedded into questions about visual stimulus properties in order to prompt novel associations. Responses to these questions could be performed either by distal or by proximal hand movements. The outcome of the word acquisition was measured using a free recall task immediately after the training and on the next day. The results showed significant differences in the success of recalling new words immediately after the learning session and on the next day only in those subjects who received cTBS of the primary motor cortex; furthermore, this effect was specific to proximal movements in both learning environments. The results suggest that the motor cortex is directly involved in acquiring novel vocabulary during active interaction with the learning material.