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

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 a(1)=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 T(1)- and T(2)-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.