should be possible to implement them (and many others) within a unified framework. We present here a general approach that accommodates most forms of experimental layout and ensuing analysis (designed experiments with fixed effects for factors, covariates and interaction of factors). This approach brings together two well established bodies of theory (the general linear model and the theory of Gaussian fields) to provide a complete and simple framework for the analysis of imaging data.The importance of this framework is twofold: (i) Conceptual and mathematical simplicity, in that the same small number of operational equations is used irrespective of the complexity of the experiment or nature of the statistical model and (ii) the generality of the framework provides for great latitude in experimental design and analysis.

This paper concerns the spatial and intensity transformations that map one image onto another. We present a general technique that facilitates nonlinear spatial (stereotactic) normalization and image realignment. This technique minimizes the sum of squares between two images following nonlinear spatial deformations and transformations of the voxel (intensity) values. The spatial and intensity transformations are obtained simultaneously, and explicitly, using a least squares solution and a series of linearising devices. The approach is completely noninteractive (automatic), nonlinear, and noniterative. It can be applied in any number of dimensions.Various applications are considered, including the realignment of functional magnetic resonance imaging (MRI) time-series, the linear (affine) and nonlinear spatial normalization of positron emission tomography (PET) and structural MRI images, the coregistration of PET to structural MRI, and, implicitly, the conjoining of PET and MRI to obtain high resolution functional images.

The recognition of dyslexia as a neurodevelopmental disorder has been hampered by the belief that it is not a specific diagnostic entity because it has variable and culture-specific manifestations. In line with this belief, we found that Italian dyslexics, using a shallow orthography which facilitates reading, performed better on reading tasks than did English and French dyslexics. However, all dyslexics were equally impaired relative to their controls on reading and phonological tasks. Positron emission tomography scans during explicit and implicit reading showed the same reduced activity in a region of the left hemisphere in dyslexics from all three countries, with the maximum peak in the middle temporal gyrus and additional peaks in the inferior and superior temporal gyri and middle occipital gyrus. We conclude that there is a universal neurocognitive basis for dyslexia and that differences in reading performance among dyslexics of different countries are due to different orthographies.

1. Differences in the distribution of relative regional cerebral blood flow during motor imagery and execution of a joy-stick movement were investigated in six healthy volunteers with the use of positron emission tomography (PET). Both tasks were compared with a common baseline condition, motor preparation, and with each other. Data were analyzed for individual subjects and for the group, and areas of significant flow differences were related to anatomy by magnetic resonance imaging (MRI). 2. Imagining movements activated a number of frontal and parietal regions: medial and lateral premotor areas, anterior cingulate areas, ventral opercular premotor areas, and parts of superior and inferior parietal areas were all activated bilaterally when compared with preparation to move. 3. Execution of movements compared with imagining movements led to additional activations of the left primary sensorimotor cortex and adjacent areas: dorsal parts of the medial and lateral premotor cortex; adjacent cingulate areas; and rostral parts of the left superior parietal cortex. 4. Functionally distinct rostral and caudal parts of the posterior supplementary motor area (operationally defined as the SMA behind the coronal plane at the level of the anterior commissure) were identified. In the group, the rostral part of posterior SMA was activated by imagining movements, and a more caudoventral part was additionally activated during their execution. A similar dissociation was observed in the cingulate areas. Individual subjects showed that the precise site of these activations varied with the individual anatomy; however, a constant pattern of preferential activation within separate but adjacent gyri of the left hemisphere was preserved. 5. Functionally distinct regions were also observed in the parietal lobe: the caudal part of the superior parietal cortex [medial Brodmann area (BA) 7] was activated by imagining movements compared with preparing to execute them, whereas the more rostral parts of the superior parietal lobe (BA 5), mainly on the left, were additionally activated by execution of the movements. 6. Within the operculum, three functionally distinct areas were observed: rostrally, prefrontal areas (BA 44 and 45) were more active during imagined than executed movements; a ventral premotor area (BA 6) was activated during both imagined and executed movements; and more caudally in the parietal lobe, an area was found that was mainly activated by execution presumably SII. 7. These data suggest that imagined movements can be viewed as a special form of "motor behavior' that, when compared with preparing to move, activate areas associated heretofore with selection of actions and multisensory integration.(ABSTRACT TRUNCATED AT 400 WORDS)