相対音感に関わる灰白質の髄鞘と神経線維束の可視化—左島皮質後部の役割

Visualization of Gray Matter Myelin and Fiber Bundles Critical for Relative Pitch: A Role of the Left Posterior Long Insular Cortex

相対音感とは外的または内的な音高に基づいて1音の高さを同定する能力である。基準音を途中で3回提示して音名を解答させる課題の成績により，参加者を3群に分けた。灰白質の髄鞘をT₁強調画像とT₂強調画像の比で可視化したところ，満点群で左島皮質後部において有意差が検出された。さらに，左島皮質と聴覚野を結ぶ線維の前方領域で満点群の方が成績下位群よりも一貫して描出できた。これらの領域は音声情報の処理に関与しており，音楽の能力が言語能力に関連すると考えられる。

Abstract

Relative pitch is the ability to identify a tone pitch based on external or internal pitches. Here we used magnetic resonance imaging (MRI) to determine which cortical region is responsible for relative pitch. Forty-eight participants were asked to listen to 24 piano tones, and then write down the names of the tones (except reference tones of a¹＝440 Hz, which were intermittently presented three times). We classified the participants into three groups based on their task scores: Group A (n＝12, full points), Group B (n＝22, 6-20 points), and Group C (n＝14, 0-5 points). We focused on the myelin of the gray matter, which can be visualized by the ratio of MR signals from a pair of T₁- and T₂-weighted images. We found significantly increased ratios in the left posterior long insular cortex for Group A. We also observed more consistent pathways in the anterior region of the left middle longitudinal fasciculus for Group A compared to Group C, which passed through the left superior temporal gyrus. Because these regions are involved in the processing of speech sounds, the present results suggest that the ability to identify musical pitches is associated with universal linguistic abilities.