12 - Functional and Structural Imaging of the Human Auditory System

Abstract

This chapter provides a brief overview of anatomical and neurophysiological data on the organization of the auditory cortex, together with some relevant behavioral data. Several findings from structural imaging and functional imaging are also reviewed. Tonotopic (or cochleotopic) organization is a ubiquitous feature of the ascending auditory nervous system, reflecting the importance of encoding information about the frequencies present in the environmental signal. However, auditory cortical areas differ both in their degree of tonotopic organization and in the sharpness of their tuning functions, with the core regions showing the sharpest tuning and most organized tonotopy, whereas belt regions exhibit more complex response functions and often have broad tuning functions. The use of structural brain imaging as a tool to understand brain organization has emerged in parallel with functional techniques. Several investigations applying these methods to the human auditory cortices, especially those using quantitative approaches, provide important data on the morphology of the relevant areas, which may eventually prove important in understanding their functional organization as well. Although a fairly large number of investigations have examined the region of the planum temporale, posterior to Heschl's gyrus (HG), few studies have used in vivo imaging techniques to look directly at the region of HG. The advent of blood oxygenation-level dependent functional magnetic resonance imaging has expanded opportunities for the noninvasive study of central auditory systems. Functional magnetic resonance imaging enables imaging at greater spatial and temporal resolution than bolus water positron emission tomography, and there are no safety restrictions on the number of images than can be made of a given individual.