視覚誘発電位を用いた大細胞系機能評価と読字能力の関連性  [in Japanese] Relationship between magnocellular function and reading skills in children: a study using visual evoked potentials  [in Japanese]

 【目的】発達性読み書き障害 (developmental dyslexia ; DD) の背景病態の一つである大細胞系機能障害を明らかにする. 【方法】7～16歳のDD児と定型発達 (typical development ; TD) 児各々19名に対し, 低空間周波数・低コントラストのサイン様白黒縦縞模様を高反転頻度で視覚提示し, 視覚誘発電位 (VEP) を記録し, 読字能力との関連を検討した. 【結果】①DD児群VEPはTD児群と比較してcomplex demodulation法によるピーク振幅が有意に低下した. ②構造方程式モデリングによりピーク振幅は線画呼称課題の成績に関連すること, 線画呼称が良好であるほど音読が向上することが見出された. 【結論】DDの病態理解に大細胞系賦活VEPは有用と考えられる.

  <i><b>Objective:</b></i> Developmental dyslexia (DD) is a neurodevelopmental disorder that is characterized by difficulties with accurate and/or fluent word recognition and by poor spelling and decoding abilities. The magnocellular deficit theory is one of several hypotheses that have been proposed to explain the pathophysiology of DD. In this study, we investigated magnocellular system dysfunction in Japanese dyslexic children. <i><b>Methods:</b></i> Subjects were 19 dyslexic children (DD group) and 19 aged-matched healthy children (TD group). They were aged between 7 and 16 years. Reversed patterns of black and white sinusoidal gratings generated at a low spatial frequency, high reversal frequency of 7.5 Hz, and low contrasts were used specifically to stimulate the magnocellular system. We recorded visual evoked potentials (VEP) from the occipital area and examined their relationship with reading and naming tasks, such as the time to read hiragana characters, rapid automatized naming of pictured objects, and phonological manipulation. <i><b>Results:</b></i> Compared to the TD group, the DD group showed a significantly lower peak amplitude of VEPs through the complex demodulation method. Structural equation modeling showed that VEP peak amplitudes were related to the rapid automatized naming of pictured objects, and better rapid automatized naming resulted in higher reading skills. There was no correlation between VEP findings and the capacity for phonological manipulation. <i><b>Conclusions:</b></i> VEPs in response to the magnocellular system are useful for understanding the pathophysiology of DD. Single phonological deficit may not be sufficient to cause DD.