Mandarin And English Writing Recruit Basal Ganglia: Evidence From PET-CT

BackgroundWriting is an advanced neural activity which can be only applied by mankind. It plays an important role in human communication. The complex writing process need not only the mutual coordination of vision, hearing and motor, but also the participation of the language, thinking, comprehension, logic and memory. Routinely, it is recognized the writing center stemming from Exner's area, the posterior portion of middle frontal gyrus of hemispheric dominance for speech. But with the continuous exploration of the research on the clinical observation, neurological imaging, pathological anatomy and psychology, more and more evidence prove that the extensive nervous net of writing involve cortical and sub-cortical structures. The two languages belong to two different systems. Mandarin is an ideogram while English is alphabetic writing. Past researches often emphasized on the relationship between the writing and the cerebral cortex. Recently, the researches often focus on the function of the writing of subcortex during the two languages separately and the results were different. Then what are the differences of the neuropsychological mechanism between the two languages? Whether or not the basal ganglia play the same role during the two different writing systems?The basal ganglia are the nuclei of gray matter deep within the cerebral cortex which are one part of extrapyramidal system including the caudate nucleus, the putamen, the globus pallidus, the dorsal thalamus and so on. Basal ganglia have long been regarded to be involved in the control of movement. With the development of the cerebral cortex, the basal ganglia degraded into subordinate component. Recently, they are proved by more and more evidence to be dedicated to nonmotor cognitive function such as memory, language, learning, reasoning and writing. Some scholars believed that the basal ganglia regarded as the third language center following the Broca's area and Wernick's area with important value to study. Clinically, some diseases with the lesion of basal ganglia, such as Parkinson's disease (PD), Huntington's disease (HD), Wilson's disease (WD) and corticobasal degeneration can often cause various disorders in writing. It provided the clues of the speculation that the basal ganglia participate in writing. However, most of the cases are not confined to the deficits associated with isolated basal ganglia damage. So it cannot be concluded whether the results were caused by the basal ganglia or the circumscribed damage. It is necessary to conduct the research on writing among normal subjects to make up for the above disadvantage.Presently, functional imaging techniques such as functional magnetic resource imaging (fMRI), magnetoencephalogram(MEG)and positron emission tomography-computer-tomography (PET-CT) can provide valid evidence to locate and identify brain areas related to writing. Due to different methods, experimental paradigm and subjects, the results were different too. Now fMRI is the main experimental technique resulting from its high spatial resolution and low cost. But it is difficult to imitate routine writing under fMRI scan and the scan time is so short, it isn't fit for the research on the continuous writing. In spite of the high temporal resolution, MEG can not detect the currents which are perpendicular to the surface of the skull. PET-CT, the molecular imaging, can get robust results through the measurement of the metabolism of the tracers. It can segregate the execution of the stimulant tasks with the scan which is fit for the research on the continuous writing. But due to the high cost, it is seldom applied to the study of writing. According to the analysis above, it is a new entry point to use PET-CT to explore the role of the basal ganglia in writing among healthy persons. In our research we conducted English writing and Mandarin writing in Indian and Chinese normal right-handed subjects. English and Mandarin can be recognized as their first languages respectively. The experimental technique was PET-CT. The experimental paradigm was active writing. By using statistical parametric mapping (SPM) we can obtain the activated area. Then we can discuss the role and the differences of the basal ganglia in the Mandarin and English writing. To go a step further we can elucidate the neuropsychological mechanism of the basal ganglia on writing.ObjectTo reveal the activation of the basal ganglia in the Mandarin and English writing by means of PET-CT. To obtain the evidence whether or not the basal ganglia participate in the Mandarin and English writing. To analysze the differences in the involvement of the basal ganglia between the Mandarin and English writing and to explore the neuropsychological mechanism.SubjectsThe subjects involved 12 healthy students learning in Sourthern medical university which were divided into Mandarin-writing group(n=6) and English-writing group(n=6). Half of them were Chinese (all males, mean age 23.67±0.82 years, ranged from 23 to 25 years), speaking Mandarin as their first language and another half Indians (all males, mean age 20.17±1.07 years, ranged from 18 to 21 years), speaking English as their first language. Participants were all consistent right-handers and they were able to write fluently. All of them received eysenck personality questionaire (EPQ) test and their personalities were identified as stable. None had a history of neurological or psychological disease. The protocol of this study was in accordance with the guidelines issued by the Committee of Medical Ethics in Nanfang Hospital. Printed informed consents were signed by all the subjects according to the Declaration of Helsinki. MethodsAll the subjects carried out two tasks at an interval of 3 to 5 days. The first task was the pseudo-writing and the second task was the Mandarin and English writing for Chinese and Indians respectively. For the pseudo-writing, Chinese drew the slash on the manuscript paper and Indians drew spiral curves on the English exercise books in a writing posture. The contents of the pseudo-writing were designed according to the characteristic of Chinese character and English letter. The Mandarin and English writing both designed as the topic fixed discourse-writing. The contents of the Mandarin and English writing could make sure the subjects write smoothly so as to accomplish the complexly active writing. The data of the pseudo-writing task and writing tasks were obtained by PET-CT. The statistical analysis of the paired-t test was used to compare pseudo-writing with writing task through the SPM2. This analysis was carried out for each group separately. The analysis of the two-sample t test was used to compare Mandarin writing with English writing through the SPM2. At last, we can get the activated area with high metabolism of glucose.Results1. Comparison of the Mandarin pseudo-writing task with the Mandarin writing task showed activation in the right caudate nucleus (P<0.01);2. Comparison of the English pseudo-writing task with the English writing task showed activation in the head of left caudate nucleus (P<0.01);3. Comparison of the Mandarin writing task with the English writing task showed activation in the right putamen (P<0.01).Conclusions1. The right caudate nucleus participates the production of Mandarin writing with an ipsilateral dominance among the right-handers; 2. The left caudate nucleus participates the production of English writing with a contralateral dominance among the right-handers;3. The right putamen was activated while comparing the production of Mandarin writing with the production of English writing. It was recruited to process the complex visuo-spatial configuration of Mandarin characters. The right basal ganglia may be the subcortical writing center, which bears a pivotal role in integrating impulses from the cortex;4. The neural net related to writing is composed of the basal ganglia, the extensive cortex and the cerebellum.