Functional fields in human auditory cortex revealed by time-resolved fMRI without interference of EPI noise

The gradient switching during fast echoplanar functional magnetic resonance imaging (EPI-fMRI) produces loud noises that may interact with the functio nal activation of the central auditory system induced by experimental acous tic stimuli. This interaction is unpredictable and is likely to confound th e interpretation of functional maps of the auditory cortex. In the present study we used an experimental design which does not require the presentatio n of stimuli during EPI acquisitions and allows for mapping of the auditory cortex without the interference of scanner noise. The design relies on the physiological delays between the onset, or the end, of stimulation and the corresponding hemodynamic response. Owing to these delays and through a ti me-resolved acquisition protocol it is possible to analyze the decay of the stimulus-specific signal changes after the cessation of the stimulus itsel f and before the onset of the EPI-acoustic noise related activation (decay- sampling technique). This experimental design, which might permit a more de tailed insight in the auditory cortex, has been applied to the study of the cortical responses to pulsed 1000 Hz sine tones. Distinct activation clust ers were detected in the Heschl's gyri and the plenum temporale, with an in creased extension compared to a conventional block-design paradigm. Further more, the comparison of the hemodynamic response of the most anterior and t he posterior clusters of activation highlighted differential response patte rns to the sound stimulation and to the EPI-noise, These differences, attri butable to reciprocal saturation effects unevenly distributed over the supe rior temporal cortex, provided evidence for functionally distinct auditory fields. (C) 2001 Academic Press.