The Cortical Organization Of Language Function In Normal Subjects And Aphasics: A Functional MRI Study

The language is a unique and important function of human brain. It' s necessary for our understanding the human brain to know the organization of language function in the brain.The neural mechanism underlying Chinese processing may be different from other alphabetic languages. Thus, research on Chinese language is helpful to elucidate the universality and specificity of the neural basis of the language.Aphasia is a common symptom in patients with brain injury. However, the mechanisms of underlying recovery of language function after brain injury are still ambiguous.We used event-related functional MRI to study the cortical organization of language function in normal native Chinese-speakers and patients with aphasia. In study one, we focused on whether the pictorial nature of Chinese word had any effect on the semantic processing of the Chinese words and whether any specific brain area was responsible for orthographic processing in Chinese word reading. We conducted the fMRI scanning when normal subjects preformed a picture-naming task and a word-generation task. The functional data were analyzed with AFNI software, which is designed for neuroimaging data processing. Comparing the activation pattern during the two working states, we found that the two tasks shared a common brain network, which was dispersed in the frontal,parietal, temporal, and occipital lobe. We also found that the activation in the ventral of right temporal-occipital junction was specific for picture naming, and the activations in the left inferior frontal gyrus and the left inferior parietal lobule were specific for word generation. We argued that the specific activation during picture naming or word generation was due to additional cognitive component or special requirement for each task. Furthermore, we found that the activation pattern for picture naming was bilateral and that for word generation was mainly left lateralized.In study two, we focused on the impact of local brain lesion on the language network and the possible mechanism underlying recovery of language function. The feasibility of functional MRI to evaluate language function in aphasia patients was also discussed. We investigated activation patterns in three aphasics when they performed the word generation task, which was contrasted separately with the pattern in normal subjects when they performed the same language tasks. The activation patterns in the aphasics were different with that in the normal subjects. None of the patients showed any activation in the left inferior frontal gyrus, where is considered to be crucial for word/verb generation task. Activations in some areas of the right hemisphere were found in two patients, which were not found in normal subjects.Main conclusions:1. Although the Chinese words are considered to be a logographic system, the processing of Chinese words is mainly left lateralized.2. Semantic processing of Chinese words and pictures dose not share a completely common system within which there are modality-specific differences.3. The activation in left BA9 during Chinese words processing may beassociated with unique square configuration of Chinese characters.4. Remote effect of focal lesion affects the cortical organization of language function in aphasics.5. Functional redistribution or reorganization may be one of the mechanisms underlying recovery of language function after brain injury.6. The fMRI study with a simple language task is useful to evaluate the cortical organization of language function in aphasia patients.