MEASUREMENTS OF THE TEMPORAL FMRI RESPONSE OF THE HUMAN AUDITORY-CORTEX TO TRAINS OF TONES

Averaged single trials (AST) allowed the functional magnetic resonance imaging (fMRI) response to auditory stimuli to be measured at high te mporal (1 s) and spatial (0.1 cm(3)) resolution. Using this paradigm w e investigated the transient signal response to 100-ms tone bursts in trains of between 100 ms and 25.5 s in total duration. We have demonst rated that the fMRI response to such auditory stimuli is approximately linear for trains of 6 s and longer, but that shorter stimuli produce signals that are larger than might be expected from the response to t he longer stimuli. This nonlinear behavior can be modeled if an adapti ve response to each stimulus is assumed. A study using a novel paradig m was also performed in order to study the influence of scanner noise during fMRI experiments on the auditory system response to tones. This study demonstrated that the temporal response to 700-ms tone stimuli is modified when performed in the presence of scanner gradient noise, the modification being a small but significant increase (P < 0.05) in the magnitude of the response. Finally the ability to measure the onse t of functional activation using the AST method was examined. It was f ound, with the aid of computer simulation that a sampling rate of one image per second is adequate to distinguish temporal responses. Using the data acquired in this study, onset times were calculated for the a uditory cortex, and these results are consistent with current models o f functional activation. (C) 1998 Academic Press.