Distinctive neural basis of anatomic imitation compared with specular imitation

我々は,解剖模倣(解剖学的に同側の四肢を使用した模倣)よりも鏡模倣を自然に実行する傾向があるが,この神経基盤はいまだに明確ではない。本研究では,fMRIを用い,鏡条件と解剖条件における左右手指運動模倣時の脳活動を比較し,解剖模倣の特性について検討した。その結果,鏡模倣に比べて解剖模倣で,両側下前頭回(IFG)と右背側運動前野(PMd)の活動が左右どちらの手を被験者が用いているかに関わらず認められた。右PMdは,被験者が解剖模倣でより注意深く,左手あるいは右手での運動表象を調整する必要があったことを示すと考えられた。左のIFGでは,鏡模倣と比較して解剖模倣において,より複雑で困難な動きをコード化している可能性が示唆された。一方,右IFGの活動は,課題の手と鏡の位置関係にある手が自然に運動しようとする動きを抑制している可能性が示唆された。Imitation plays a very important role in human cognition and communicative competence. Individuals tend to imitate the hand actions of another person as if looking in a mirror (specular imitation) than with the anatomically congruent hand (anatomic imitation). We focused on the problem why anatomic imitation is more difficult than specular imitation. To understand the neural substrates of the anatomic imitation versus the specular imitation with the left or right hand, eleven normal female subjects who imitated the finger movements of an actor using the anatomically congruent or incongruent hand were examined using functional magnetic resonance imaging (fMR1). As a result, the error rate tended to be higher for anatomic imitation than for specular imitation, and the bilateral inferior frontal gyrii (IFG) and the right dorsal premotor cortex (PMd) were activated during anatomic imitation versus specular imitation, irrespective of the hand used. Especially the right IFG activity may inhibit the motor representation associated with the preferred movement of imitating the actor\u27s hand movement as if looking in a mirror. The right PMd which was activated during anatomic imitation might be involved in some difficulties associated with the imitation in which the subjects were required to carefully and internally coordinate the motor representation of the left and right hands. On the other hand, the left IFG might encode more complex and difficult goal compared with that in the specular imitation