Probabilistic atlases of neuroanatomy are more representative of population anatomy than single brain atlases. They allow anatomical labeling of the results of group studies in stereotaxic space, automated anatomical labeling of individual brain imaging datasets, and the statistical assessment of normal ranges for structure volumes and extents. No such manually constructed atlas is currently available for the frequently studied group of young adults. We studied 20 normal subjects (10 women, median age 31 years) with high-resolution magnetic resonance imaging (MRI) scanning. Images were nonuniformity corrected and reoriented along both the anterior-posterior commissure (AC-PC) line horizontally and the midsagittal plane sagittally. Building on our previous work, we have expanded and refined existing algorithms for the subdivision of MRI datasets into anatomical structures. The resulting algorithm is presented in the Appendix. Forty-nine structures were interactively defined as three-dimensional volumes-of-interest (VOIs). The resulting 20 individual atlases were spatially transformed (normalized) into standard stereotaxic space, using SPM99 software and the MNI/ICBM 152 template. We evaluated volume data for all structures both in native space and after spatial normalization, and used the normalized superimposed atlases to create a maximum probability map in stereotaxic space, which retains quantitative information regarding inter-subject variability. Its potential applications range from the automatic labeling of new scans to the detection of anatomical abnormalities in patients. Further data can be extracted from the atlas for the detailed analysis of individual structures.

In pursuing our work on the organization of human visual cortex, we wanted to specify more accurately the position of the visual motion area (area V5) in relation to the sulcal and gyral pattern of the cerebral cortex. We also wanted to determine the intersubject variation of area V5 in terms of position and extent of blood flow change in it, in response to the same task. We therefore used positron emission tomography (PET) to determine the foci of relative cerebral blood flow increases produced when subjects viewed a moving checkerboard pattern, compared to viewing the same pattern when it was stationary. We coregistered the PET images from each subject with images of the same brain obtained by magnetic resonance imaging, thus relating the position of V5 in all 24 hemispheres examined to the individual gyral configuration of the same brains. This approach also enabled us to examine the extent to which results obtained by pooling the PET data from a small group of individuals (e.g., six), chosen at random, would be representative of a much larger sample in determining the mean location of V5 after transformation into Talairach coordinates. After stereotaxic transformation of each individual brain, we found that the position of area V5 can vary by as much as 27 mm in the left hemisphere and 18 mm in the right for the pixel with the highest significance for blood flow change. There is also an intersubject variability in blood flow change within it in response to the same visual task. V5 nevertheless bears a consistent relationship, within each brain, to the sulcal pattern of the occipital lobe. It is situated ventrolaterally, just posterior to the meeting point of the ascending limb of the inferior temporal sulcus and the lateral occipital sulcus. In position it corresponds almost precisely with Flechsig's Feld 16, one of the areas that he found to be myelinated at birth.

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To assess the effect of stimulus correlated motion on the appearance of functional magnetic resonance images, conventional visual and motor protocols were each performed by four normal volunteers and an image co-registration technique was used to retrospectively monitor subject motion. In three studies synthetic data sets were constructed from single baseline images using the positional information obtained from the co-registration procedure. Cumulative difference images were then created from both the synthetic and functional image sets. Stimulus correlated motion was detected in all eight studies and the synthetic cumulative difference images showed striking similarities to the equivalent functional images in each case.