Modulation and task effects in auditory processing measured using fMRI

Active listening has been reported to elicit a different sensory response f rom passive listening and is generally observed as an increase in the magni tude of activation. Sensory activation differences may therefore be masked by the effect of attention. The present study measured activation induced b y static and modulated tones, while controlling attention by using target-d iscrimination and passive listening tasks. The factorial design enabled us to determine whether the stimulus-induced activation in auditory cortex was independent of the information-processing demands of the task. Contrasted against a silent baseline, listening to the tones induced widespread activa tion in the temporal cortex, including Heschl's gyrus (HG), planum temporal e, superior temporal gyrus (STG), and superior temporal sulcus. No addition al auditory areas were recruited in the response to modulated tones compare d to static tones, but there was an increase in the response in the STG, an terior to HG. Relative to passive listening, the active task increased the response in the STG, posterior to HG. The active task also recruited region s in the frontal and parietal cortex and Subcortical areas. These findings indicate that preferential responses to the changing spectro-temporal prope rties of the stimuli and to the target-discrimination task involve distinct , non-overlapping areas of the secondary auditory cortex. Thus, in the pres ent study, differences in sensory activation were not masked by the effects of attention. (C) 2000 Wiley-Liss, Inc.