Analysis of working memory using the reading span test : basic research of regional brain activity on brain cortex using functional near-infrared spectroscopy

本稿では,言語性ワーキングメモリ課題であるリーディングスパンテストを用いて,ワーキングメモリ容量と脳血流の関係の検討を行った.脳血流量変化は脳活動を評価する指標の一つである.機能的近赤外分光法(fNIRS)は,脳血流の変化を検出するための非侵襲装置である.そのため,脳活動の活性化領域を把握することができる.本稿では,前頭前野背外側部(DLPFC)と左下前頭回(LIFG)を関心領域(ROI)として着目した.これらの関心領域の機能的な活性化はfNIRSを用いて検討した.DLPFCは注意の維持を行い,LIFGは言語処理を司るとされている.実験により以下の3点が得られた.まず,DLPFCとRSTの間で機能的な関係がみられた.被験者を高成績群と低成績群の二つのグループに分類したところ,低成績群の脳血流量変化は高成績群の脳血流量変化に比べて活性が大きかった.次に,両群においてLIFGでは活性パターンに違いがみられた.高成績群では活性が持続していたのに対し,低成績群では活性が低下した.最後に,低成績群のみにおいてDLPFCの活性が上昇した.In this paper, the relationship between a working memory capacity and a brain activity were evaluated using the results of a Reading Span Test (RST), which is a language working memory task. A cerebral blood flow change is one of the indexes of evaluating brain activities. functional Near-infrared Spectroscopy (fNIRS) is a non-invaded device to detect a cerebral blood flow change, so that it can be used to figure out the activated area of brain activities. In this paper, we focus on dorsolateral prefrontal cortex (DLPFC) and the left inferior frontal gyrus (LIFG) as regions of interests (ROI). Functional activation of these ROIs was examined using fNIRS. It has been reported that DLPFC is responsible for continuing cautions, while LIFG manages language processing. Through the experiments, the following three points were observed. First, the functional relation between DLPFC and RST was observed. The subjects were classified into two groups; a high score and a low score groups. The cerebral blood flow changes in of the subjects in the low score group were greater than that of the subjects in the high score group. Second, in the both groups, LIFG was activated with the different active patterns; In LIFG, the brain activity was constant for in the high score group, while it was declining in the low score group. Lastly, the brain activity in the DLPFC region for the low score group increased