LATENCIES IN FMRI TIME-SERIES - EFFECT OF SLICE ACQUISITION ORDER ANDPERCEPTION

In BOLD fMRI a detailed analysis of the MRI signal time course sometim es shows time differences between different activated regions. Same re searchers have suggested that these latencies could be used to infer t he temporal order of activation of these cortical regions, Several eff ects must be considered, however, before interpreting these latencies. The effect of a slice-dependent time shift (SDTS) with multi-slice ac quisitions, for instance, may be important for regions located on diff erent slices, After correction for this SDTS effect the time dispersio n between activated regions is significantly decreased and the correla tion between the MRI signal time course and the stimulation paradigm i s improved, Another effect to consider is the latency which may exist between perception and stimulus presentation. It is shown that the con trol of perception can be achieved using a finger-spanning technique d uring the fMRI acquisition. The use of this perception profile rather than an arbitrary waveform derived from the paradigm proves to be a po werful alternative to fMRI data processing, especially with chemical s enses studies, when return io baseline Is not always correlated to sti mulus suppression. This approach should also be relevant to other kind s of stimulation tasks, as a realistic way of monitoring the actual ta sk performance, which map depend on attention, adaptation, fatigue or ee en variability of stimulus presentation. (C) 1997 John Wiley & Sons , Ltd.