**4. Conclusion**

102 Neuroimaging – Cognitive and Clinical Neuroscience

While different processing systems are utilized in the early stages of the language process (i.e., modality-related processes (i.e., visual and auditory input) and the processing of non-linguistic to linguistic information translation), a common word recognition system exists in the late stages of the process (i.e., phonological processing, semantic processing, and sentence processing). Findings suggest that the inferior frontal and inferior parietal regions are associated with working memory load and/or phonological processing to perform experimental tasks for single word processing. The left inferior frontal region is malso suggested to be associated with intended acts, planning, and/or cognitive control to resolve competition, which have common processes with other cognitive functions (Owen et al., 2005; January et al., 2008; Yokoyama et al., 2009b). Thought to be involved in the semantic processing of words are the orbito-frontal and parietal "retrieval" system, and the temporal "storage" system (i.e., long term memory). Also, sensorimotor areas have been shown to be activated during word and sentence comprehension tasks. Their activation may be due to sensorimotor experiences which induce the storage of long term memories in the sensorimotor areas. While sentence comprehension activates the left inferior frontal and dorsal prefrontal cortex, these activations are thought to be based on phonological working memory and executive functions. Taken together, language comprehension would be supported by the neural substrates of the working memory and

Fig. 3. Brain mapping of language function.

Through a review of the literature we find that, since the neural basis of language comprehension overlaps that of other cognitive systems, mainly the memory system regionwise, most previous neuroimaging studies support the "generalist" view. However, it is to be noted that the overlaps of the neural substrate may not indicate a functional overlap since there exists a possibility that, while a brain region is commonly activated for both processes, the brain region plays different roles between them. In future studies, to clarify which brain region or cognitive process is common for language comprehension and other cognitive systems, and which is different between them, it will be necessary to develop a new experimental paradigm and also a new data analysis method, such as the functional/effective connectivity and multi-voxel pattern analysis. These methods should then be applied to language comprehension studies. Additionally, it will be necessary to consider the relationship between language and memory functions in language acquisition (i.e., Yokoyama et al., 2006a; 2009a), since, at this time, findings in neuroimaging studies regarding this issue are very few. Examination of whether or not and how semantic memory is related to the acquisition of lexico-semantic information, as well as whether or not and how procedural memory is responsible for proficienct gramatical processes such as morphological processing and sentence structure computation, might also be necessary.
