<i>In Vivo</i>Functional and Myeloarchitectonic Mapping of Human Primary Auditory Areas

TLDR

In contrast to vision, where retinotopic mapping alone can define areal borders, primary auditory areas such as A1 are best delineated by combining in vivo tonotopic mapping with postmortem cyto‑ or myeloarchitectonics from the same individual. The study aims to use a multimodal approach to define the auditory core, facilitating investigations of structure–function relationships, comparative neuroanatomical studies, and new biomarkers for diagnosis and clinical studies. The authors combined high‑resolution (800 µm) quantitative T1 mapping with phase‑encoded tonotopic methods to delineate primary auditory areas A1 and R within the auditory core of human volunteers. The study quantitatively characterized the highly myelinated auditory core, revealing two mirror‑image tonotopic maps aligned along the same axis as in macaque and owl monkey, corresponding to human A1 and R, and found that the core occupies a smaller portion of tonotopically organized cortex than previously assumed.

Abstract

In contrast to vision, where retinotopic mapping alone can define areal borders, primary auditory areas such as A1 are best delineated by combining in vivo tonotopic mapping with postmortem cyto- or myeloarchitectonics from the same individual. We combined high-resolution (800 μm) quantitative T 1 mapping with phase-encoded tonotopic methods to map primary auditory areas (A1 and R) within the “auditory core” of human volunteers. We first quantitatively characterize the highly myelinated auditory core in terms of shape, area, cortical depth profile, and position, with our data showing considerable correspondence to postmortem myeloarchitectonic studies, both in cross-participant averages and in individuals. The core region contains two “mirror-image” tonotopic maps oriented along the same axis as observed in macaque and owl monkey. We suggest that these two maps within the core are the human analogs of primate auditory areas A1 and R. The core occupies a much smaller portion of tonotopically organized cortex on the superior temporal plane and gyrus than is generally supposed. The multimodal approach to defining the auditory core will facilitate investigations of structure–function relationships, comparative neuroanatomical studies, and promises new biomarkers for diagnosis and clinical studies.