Mechanisms of writing]

Writing impairments are caused by various different mechanisms and lesions. The left posterior inferior temporal lobe plays the important role in retrieving the morphograms of the characters. Therefore the lesions involving this region have more effect on Kanji (Japanese morphogram) than on Kana (Japanese phonogram). The angular gyrus is considered to maintain the retrieved letter/character information and convert the naive information into writing performance. Sometimes Kana dominant impairment is detected due to this lesion because in some persons may have the direct route from phonemic presentation into writing execution process without definite retrieval of its form or morphology. The left superior parietal lobule is associated to the writing execution, thus, the lesion in this region induces the impairment of writing stroke and ill-shaped characters. The posterior part of the left middle frontal gyrus is related to select and arrange the letters to make a word, so the lesion in this area will develop paragraphia, in particular replacement of the letters within a word. Recently, the typing of the keyboard is becoming more popular in our everyday life. Reflecting this phenomenon, specific typing impairment called dystypia is reported. It is supposed that there is the impairment between linguistic process and typing execution.