Reproducibility of human functional MRI (fMRI) studies is essential for clinical and neuroresearch applications of this new human brain mapping method. Based on a recently presented study on reproducibility of gradient-echo fMRI in the human visual cortex (Moser et al. Magn Reson Imaging 1996; 14:567-579), comparing the performance of three different threshold strategies for correlation analysis, we demonstrate that (a) fuzzy clustering is a robust, model-independent method to extract functional information in time and space; (b) intertrial reproducibility of cortical activation is significantly improved by the capability of fuzzy clustering to separate signal contributions from larger vessels, running perpendicular to the slice orientation, from activation apparently close to the primary visual cortex; and (c) for repeated single subject studies, SDs of <20% for signal enhancement in approximately 80% of the studies and SDs of <30% for activated area size in approximately 65% of the studies are obtained. This, however, depends also on signal-to-noise ratio, (motion) artifacts, and subject cooperation.

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The technique of functional magnetic resonance imaging (FMRI) allows the measurement of functional cerebral blood flow changes occurring with specific tasks. However, the spatial relationship between neuronal activity and functional cerebral blood flow changes is not known yet. This study compares the centre of neuronal activation (measured by magnetoencephalography) with that of the blood flow response (measured by FMRI) to unilateral motor stimulation in eight subjects. The results show a mean localization difference of 1.6 cm and demand application of methodological improvements as recently suggested.

The validity of functional magnetic resonance imaging (FMRI) brain maps with respect to the sites of neuronal activation is still unknown. One source of localization error may be pixels with large signal amplitudes, since such pixels may be expected to overlie large vessels, running remote from the centre of neuronal activation. In this study, magnetoencephalography was used to determine the centre of neuronal activation in a simple finger tapping task. The localization accuracy of conventional FMRI depending on FMRI signal enhancement was investigated relative to the magnetoencephalography reference. The results show a deterioration of FMRI localization with increasing signal amplitude related to increased contributions from large vessels. We conclude that FMRI data analysis should exclude large signal amplitudes and that magnetoencephalography may help to improve FMRI brain mapping results in a multimethod approach.

Conventional functional magnetic resonance imaging (FMRI) allows the measurement of functional cerebral blood flow changes occurring with specific tasks using standard clinical MR systems. However, the spatial relationship between neuronal activity and functional cerebral blood flow changes is not yet known. This article reviews studies which compared the center of neuronal activation (measured by magnetoencephalography) with that of the hemodynamic response (measured by FMRI) using motor and visual stimulation. 0 1995 John Wiley 8 Sons, Inc.