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Abstract:
The role played by sensory and motor cortices in recognition memory is highly debated. According to the predictive coding theory of multisensory learning, sensory and motor brain regions that encode multisensory information during learning may support later recognition of learned stimuli, even under unisensory recognition conditions. We used the neurodisruptive effects of inhibitory transcranial magnetic stimulation (TMS) to investigate whether sensorimotor cortical responses causally contribute to the auditory translation of foreign language (L2) vocabulary following multisensory L2 training. Twenty-two participants learned L2 words and their native language translations over 4 consecutive days. Words were learned in two conditions: In one condition, participants viewed and performed gestures as L2 words were auditorily-presented, and in a control condition, participants viewed pictures as L2 words were auditorily-presented. Gestures and pictures were congruent with word meanings. Following training, participants underwent effective and sham TMS as they listened to the L2 words that they had learned and translated the words into their native language.We targeted with TMS a region near the boundary of motor and somatosensory cortices (Brodmann area 4) in both the right hemisphere (offline theta-burst TMS) and left hemisphere (online repetitive TMS). Responses in this region were previously found to correlate with the behavioral benefits of performing gestures during L2 vocabulary learning. As expected, the application of TMS slowed translation response times for L2 words that had been learned by performing gestures compared to sham stimulation. TMS did not affect translation response times for words learned while viewing pictures compared to sham stimulation. This result suggests that gesture-based learning induced changes in L2 representations within motor and somatosensory cortices, which in turn facilitated the translation of L2 words. Specialized sensory and motor cortices may therefore play a causal role in remembering the native language translation of an L2 word following multisensory encoding.
