The exact anatomical localization of right hemisphere lesions that lead to left spatial neglect is still debated. The effect of confounding factors such as acute diaschisis and hypoperfusion, visual field defects, and lesion size may account for conflicting results that have been reported in the literature. Here, we present a comprehensive anatomical investigation of the gray- and white matter lesion correlates of left spatial neglect, which was run in a sample 58 patients with subacute or chronic vascular strokes in the territory of the right middle cerebral artery. Standard voxel-based correlates confirmed the role played by lesions in the posterior parietal cortex (supramarginal gyrus, angular gyrus, and temporal–parietal junction), in the frontal cortex (frontal eye field, middle and inferior frontal gyrus), and in the underlying parietal–frontal white matter. Using a new diffusion tensor imaging-based atlas of the human brain, we were able to run, for the first time, a detailed analysis of the lesion involvement of subcortical white matter pathways. The results of this analysis revealed that, among the different pathways linking parietal with frontal areas, damage to the second branch of the superior longitudinal fasciculus (SLF II) was the best predictor of left spatial neglect. The group study also revealed a subsample of patients with neglect due to focal lesion in the lateral–dorsal portion of the thalamus, which connects the premotor cortex with the inferior parietal lobule. The relevance of fronto-parietal disconnection was further supported by complete in vivo tractography dissection of white matter pathways in 2 patients, one with and the other without signs of neglect. These 2 patients were studied both in the acute phase and 1 year after stroke and were perfectly matched for age, handedness, stroke onset, lesion size, and for cortical lesion involvement. Taken together, the results of the present study support the hypothesis that anatomical disconnections leading to a functional breakdown of parietal–frontal networks are an important pathophysiological factor leading to chronic left spatial neglect. Here, we propose that different loci of SLF disconnection on the rostro-caudal axis can also be associated with disconnection of short-range white matter pathways within the frontal or parietal areas. Such different local disconnection patterns can play a role in the important clinical variability of the neglect syndrome.

Recent advances in functional neuroimaging of the human cerebral cortex revived interest in the study of the cortical morphology at both macro- and microscopic levels. By means of high-resolution magnetic resonance imaging (MRI), in vivo images of the human brain can be acquired and used to aid localization of the functional maps. The goal of the present study was to determine variability in the occurrence and location of the cingulate sulcus (CS) and the paracingulate sulcus (PCS). Brain MRIs of 247 healthy young volunteers were obtained and tranformed into a standardized stereotaxic space (Talairach and Tournoux. 1988). The CS and PCS were marked in 494 hemispheres using software capable of real-time movement through a 3-D volume. The markers were used to generate a probabilistic map of the CS and PCS. The individual MRI images were also evaluated for the presence and location of the following morphological features: the continuity of the CS, the presence of vertically oriented branches of the CS, the presence of the PCS, and the presence of the intralimbic sulcus. The results revealed considerable variability in the location of some of the above morphological features and a striking hemispheric asymmetry in the prominence of the PCS. The results of four previous blood-flow activation studies of speech control were used to illustrate the relevance of our morphological findings for functional neuroimaging of the human anterior cingulate cortex.