The Influence Of The Words Frequency And Age Of Acquisition On The Processing Based Predilection Of Left Inferior And Middle Frontal Gyrus

The age of acquisition and frequency also proved to be two significant variables in word processing. In the previous studies, the selection of frequency range was unsubstantiated and considerable variability among different studies, moreover, the definitions of early and late in words acquisition were different too. The results of the brain imaging studies on the age of acquisition and word frequency were inconsistent. The functional connectivity of the left and right brain areas has not been reported.In experiment 1, was aimed to explore the influence of word frequency on the activation of the left inferior and middle frontal gyrus in language processing.,we selected words from percentage database of Modern Chinese Frequency Dictionary as the experiment materials. The words, chose from the words whose percentile rank were above 80%, were used as high-frequency words, the percentile rank of low-frequency words was lower than 20%, Native Cantonese students from Guang Zhou University participated in this study. The fMRI experiment was performed using a 1.5T Philips Achieva MRI scanner. The results showed that the high-frequency Cantonese Chinese characters activated the left inferior frontal gyrus, while the low-frequency words activated the left middle frontal gyrus (BA9/BA6). The high frequency Mandarin Chinese characters activated the left middle frontal gyrus (BA9/BA6), while the low frequency ones only activated BA9 of the left middle frontal gyrus. The statistical results of correlation among activating areas revealed that the left inferior frontal gyrus and right superior frontal gyrus, activated in the high-frequency Cantonese Chinese characters task, were functional connectivity areas. Meanwhile, there is a strong correlation between left middle frontal gyrus and right medial frontal gyrus in both low-frequency conditions and high frequency Mandarin Chinese characters condition. The neural networks for Chinese characters processing were different from that for alphabetic writing language, it was not frontal- temporal, but frontal- the right side of the brain, and the connection pattern were various under different conditions.The results of experiment 1 indicated that the words frequency couldn't explain the different processing preference of the left inferior and middle frontal gyrus. For subjects, Cantonese, as thire first language, was early acquired, while Mandarin was late acquired. Therefore we hypothesized the major cause of this maybe the age of acquisition.In experiment 2, we chose early/late acquired words from the words whose percentile rank were above 80%, as well as its English translation as experiment materials. The subjects were homogeneous with experiment 1, to explore the influence of the age of acquisition on the activation of the left inferior and middle frontal gyrus in semantic processing. The results showed that the high-frequency early acquired Cantonese words as well as its English translation activated the left inferior frontal gyrus, while the high-frequency late acquired words activated the left middle frontal gyrus (BA9/BA6). There wad no major language area activated in the comparison between the language.The results of the two experiments indicated that the high-frequency early acquired words were processed in left inferior frontal gyrus, late acquired written words were in the left middle frontal gyrus. The storage of language processing in the brain follows the chronological and space saving principles.