吃音の脳科学

The neuronal basis of stuttering

　脳機能画像法による吃に関する最近の研究を概括し，非流暢発話を引き起こす脳機構に関して考察した．特に伝統的な右半球優位原因説の詳細な再検討を要請する研究に注目した．脳磁図や機能的MRIを用いたいくつかの研究は，言語処理と発話運動制御を受け持つそれぞれの脳領野間の時間的相互作用や情報伝達に制約があること，右半球優位は吃を軽減しようとする補償的な現象である可能性を示唆している．吃の原因を明らかにするためには，吃の発達過程で起こる脳機能編成，再編成の詳細な検討が重要だと思われる．

　Latest brain imaging studies on stuttering are reviewed to discuss possible neural mechanisms causing speech disfluencies.　The emergence of brain imaging has increased interest in exploring the long-held notion that people who stutter have greater right hemisphere involvement in speech production than fluent speakers.　Recent brain imaging studies have shown profound timing disturbances between areas involved in language preparation and speech motor execution in the left hemisphere, suggesting that persistent developmental stuttering might be related to impaired neuronal communication within these cortical areas and that right hemisphere overactivation merely reflects a compensatory mechanism.　To uncover the neuronal basis of persistent developmental stuttering and to understand how this dysfunctional system emerges, it seems important that noninvasive studies be conducted with children who stutter during the critical period for speech development.