[The time-course change of brain activity during learning new movement patterns of pronunciation with orthodontic appliances and its correlation with self-evaluation of pronunciation difficulty: an fMRI study].

Pronunciation requires speed and accuracy, like many other fundamental activities such as breathing, eating, and walking. People can pronounce almost automatically without paying much attention to correctness, also like other activities. However, people may have to focus carefully on pronunciation when learning a foreign language, wearing dental appliances or rehabilitating after an injury or disease that affects speech. In the present study, we investigated neural changes underlying the process of learning new movement patterns of pronunciation in such cases. Nine healthy adults participated in the study. Difficulty of pronunciation was evaluated and cortical activity was measured under three conditions (overt and covert speaking, and silent reading) by fMRI three times after they wore orthodontic appliances. We found that the right superior temporal gyrus (STG) was involved in the auditory feedback control of pronunciation with the appliances, and the activity of the right STG was well correlated with the subjective difficulty of pronunciation and its time-dependent reduction. On the other hand, neural changes related to somatosensory feedback control and motor control of pronunciation did not show any time-dependent change. Our findings indicate that auditory feedback control of pronunciation is more important than motor control and somatosensory feedback control for learning new movements related to pronunciation.