IMAGING SUBCORTICAL AUDITORY ACTIVITY IN HUMANS

There is a lack of physiological data pertaining to how listening huma ns process auditory information. Functional magnetic resonance imaging (fMRI) has provided some data for the auditory cortex in awake humans , but there is still a paucity of comparable data for subcortical audi tory areas where the early stages of processing take place, as amply d emonstrated by single-unit studies in animals. It is unclear why fMRI has been unsuccessful in imaging auditory brain-stem activity, but one problem may be cardiac-related, pulsatile brain-stem motion. To exami ne this, a method eliminating such motion (using cardiac gating) was a pplied to map sound-related activity in the auditory cortices and infe rior colliculi in the brain stem. Activation in both the colliculi and cortex became more discernible when gating was used. In contrast with the cortex, the improvement in the colliculi resulted from a reductio n in signal variability, rather than from an increase in percent signa l change. This reduction is consistent with the hypothesis that motion or pulsatile flow is a major factor in brain-stem imaging. The way no w seems clear to studying activity throughout the human auditory pathw ay in listening humans. (C) 1998 Wiley-Liss, Inc.