In Juelich and Duesseldorf cytoarchitectonic areas were analyzed and spatially normalized to ECHBD space. These Cytoarchitectonic Maps were then transformed into the MNI space to enable researcheres to easily analyze structure and function in the human brain.
For the localization of activated regions identified by functional imaging an overlay with an anatomical atlas is required. However, there is considerable intersubject structural variability, caused by different macroscopical anatomy, as reflected by a different sulcus pattern, and by different location and extent of cortical areas, which can only be defined microscopically. Therefore, only the spatial normalization of the macroscopical anatomy of an MRI brain dataset to a common reference system permits statements about the structural intersubject variability of architectonic areas and their correlation to functional activations.
In Juelich and Duesseldorf (http://www.fz-juelich.de/ime/) cytoarchitectonic areas have already been analyzed and spatially normalized to ECHBD space. The ICBM 452 space is used within the ICBM consortium and large parts of the neuroscientific community for functional data analysis. Maps of the motor and somatosensory cortex, the auditory cortex, the visual cortex and Broca’s region, and fiber tracts have already been published. However, within SPM, widely used for functional data analysis, brains are normalized to ICBM 452 space. Preceding studies showed the benefit of an overlay of cytoarchitectonic maps and SPM data. Therefore the transformation of the cytoarchitectonic maps into the MNI space is desirable for an easy structural-functional analysis.
Sixteen adult human brains were fixed in formalin or Bodian’s fixative, scanned with a 3-D MPRAGE sequence, embedded in paraffin, sectioned coronally or sagittally at 20 µm, and stained for cell bodies or fiber tracts. Borders of the areas were defined by an observer independent statistical analysis on the basis of differences in the cortical architecture. Histological volumes were 3-D reconstructed and automatically corrected for linear and nonlinear deformations due to histological processing. The reconstructed histological volumes were warped to the individual ICBM 452 reference brain (an average of 27 scans of the same subject using nonlinear, elastic warping algorithms. The fixation of the postmortem brains occurring before MRI acquisition alters the signal, e.g. resulting in a totally different intensity distribution. We used the MNI's MRI simulator to change the gray value distribution by creating a T2 contrast version of the ICBM 452 reference brain in order to get a comparable image intensity distribution between a postmortem brain and the in vivo MRI reference brain. The deformation fields were applied to each of the individual areas. The transformed areas were superimposed to the reference brain, and probability maps were calculated which quantified the intersubject variability in their location and extent.
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