fMRI of the Central Auditory System

Over the years, blood oxygen level-dependent (BOLD) fMRI has made important contributions to the understanding of central auditory processing in humans. Although there are significant technical challenges to overcome in the case of auditory fMRI, the unique methodological advantage of fMRI as an indicator of population neural activity lies in its spatial precision. It can be used to examine the neural basis of auditory representation at a number of spatial scales, from the micro-anatomical scale of population assemblies to the macro-anatomical scale of cortico-cortical circuits. The spatial resolution of fMRI is maximized in the case of mapping individual brain activity, and here it has been possible to demonstrate known organizational features of the auditory system that have hitherto been possible only using invasive electrophysiological recording methods. Frequency coding in the primary auditory cortex is one such example that we shall discuss in this chapter. Of course, non-invasive procedures for neuroscience are preferable. As the field moves toward this goal by recording in awake, behaving animals, human neuroimaging techniques will be increasingly relied upon to provide an interpretive link between animal neurophysiology at the multi-unit level and the operation of larger neuronal assemblies. This comparative approach is crucial for the ultimate aim to understand the mechanisms of auditory perception. For example, the neural effects of intentional behavior on stimulus-driven coding have been explored both in animals, using electrophysiological techniques, and in humans, using fMRI. While the feature-specific effects of selective attention are well established in the visual cortex, the effects of auditory attention in the auditory cortex are only just starting to be revealed. Each section considers some future directions for auditory fMRI research.