[Biological significance of Broca's region]

Since P. Broca (France) reported in 1960's the case with disturbance of speech caused by the left infero-posterior frontal lesion, this region was considered to be a kineticism speech center (Broca's area: BA). Linguistic functions have been clarified afterwards by many studies and case reports. Doubt whether the former BA where Homo Sapiens got a linguistic functions would take any kind of function is left as expected. We have faced an original function of BA based on results provided accidentally in our studies related to sensori-motor linkage mechanisms. Then, we have clarified brain function about non-linguistic processing. BA and the primary motor area (M1) were activated approximately at the same level, when a subject observed and performed the same actions by herself as ones of another person. In case that she imitated actions of another person, activities of BA and M1 increased significantly (Human Mirror Neuron System: HMNS). Subjects with Asperger's syndrome are impaired in social interaction and imitation of action showed abnormal processing of HMNS in BA and M1 which could account for a part of imitation and social impairments. These results converge on a central role of Broca's area as an orchestrator of time sensitive perceptual and motor functions underlying and non-verbally social communication.