r Spatial Heterogeneity in Language Lateralization r Figure 3. A: Multidimensional scaling projection of the distance between Effect size of left and right angular and ventral precentral gyri dur- the 50 clusters (numbered from 1 to 50). The regions belonging ing semantic matching on words and pictures. This displays the to the most distant clusters (clusters 45 and 49) are displayed on mean parameter estimates over all subjects that code the differen- axial slices. B: Scatter-plot of the negative correlation between lat- ces in activation signal during semantic versus perceptual match- erality in the angular gyrus (cluster 45) and ventral precentral ing. SW, semantic word matching; SP, semantic picture matching; gyrus (cluster 49). Each subject is shown by a circle-dot shape. C: PM, perceptual matching on unfamiliar stimuli. right hemisphere, it is not surprising that patients also show wide variability in right hemisphere language activation fol- lowing damage to the dominant left-hemisphere. Regional Dissociation in Laterality Our second ﬁnding, that language lateralization has high spatial heterogeneity, also has clinical implications because it implies that one global laterality value is not sufﬁcient to reﬂect the underlying spatial variability [Josse and Tzourio-Mazoyer, 2004], irrespective of how laterality is assessed at the global level. The opposing effects of lat- erality that we observed in the angular gyrus and the ven- tral precentral gyrus (see Fig. 3) are particularly interesting because they indicate that, when healthy subjects have increased left lateralization in the angular gyrus they also had decreased left lateralization in the ventral precentral activation, even though the stimuli and task are held con- stant across subjects. This contrasts to rare observations of r 1609 r