Brain Voyager QX 1.9 (Brain Innovation, Maastricht, The Nederlands) was used for image data preparation and processing. The first 3 functional volumes were discarded to ensure steady-state longitudinal magnetization. The remaining functional image time-series were first corrected for the differences in slice acquisition times, detrended, realigned with T1-volumes and transformed into the standard Talairach anatomical space (Talairach and Tournoux, 1988). For each dataset, spatial ICA was applied to the fMRI time-series (McKeown at al., 1998). After data reduction by means of principal component analysis (PCA), ICs were estimated by means of the FastICA algorithm (Hyvärinen, 1999). Each fMRI IC consisted of a waveform and a spatial map: the waveform corresponded to the time-course of the specific pattern; the intensity of this activity across voxels was expressed by the associated spatial map. To display voxels contributing most strongly to a particular IC and to allow inter-subject comparison, the intensity values in each map were scaled to z-scores (McKeown et al., 1998). In general, the spatial maps were characterized by areas with positive and negative z-scores, assumed to reflect stimulation-induced activation and deactivation, respectively.
