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Anatomy - PowerPoint PPT Presentation

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Anatomy
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  1. Anatomy • What is the difference between Structural Anatomy and Functional Anatomy? • What roles do each play in our understanding of the brain?

  2. Structural Anatomy • Brain structures are identified in a hierarchical fashion (with substantial randomness) • Heispheres -> Lobes -> Sulci & Gyri • Sulci and Gyri are all named • but somewhat variable across individuals

  3. Structural Anatomy • Brodmann Areas defined by cytoarchitecture • map of variations in cellular morphology

  4. Connectivity • Anatomists are concerned with brain regions and how they are interconnected • Interconnectedness occurs at various levels: • interneurons • cortico-cortical connections • thalamo-cortical and cortico-thalamic • afferent = “to” (e.g. sensory) and efferent = “from” (e.g. motor)

  5. Connectivity • How do anatomists study connectivity? • Retrograde Tracers (e.g. horseradish peroxidase) follow axons back to where they came from • Anterograde Tracers (e.g. dextran) follow axons to where they are going • Diffusion Tensor Imaging (DTI) • MRI Technique that traces long white matter tracts

  6. Connectivity • “Ascending” and “descending” projections in sensory systems • estimate: for every ascending projection there are ten descending projections

  7. Connectivity • “Ascending” and “descending” projections in sensory systems • estimate: for every ascending projection there are ten descending projections Why would we have descending projections?

  8. Connectivity • It is the inter-connectivity of the brain that (probably) allows it to perform the vastly complex processes of cognition

  9. Structural and Functional Imaging • There are a number of well known techniques to create images of brain anatomy • CAT scan, MRI, X-Ray, • Note however that structural and functional images are not the same thing!

  10. Structural and Functional Imaging • There are a number of well known techniques to create images of brain anatomy • CAT scan, MRI, X-Ray, • Note however that structural and functional images are not the same thing! • Which is more useful?

  11. Structural and Functional Imaging • This is a Functional MRI Image !?

  12. Structural and Functional Imaging • This is a structural MRI image (an “anatomical” image)

  13. Structural and Functional Imaging • What you really want is both images co-registered

  14. Structural and Functional Imaging • What you really want is both images co-registered • Why? What’s wrong with the functional image alone?

  15. Structural and Functional Imaging • Functional images tend to be lower resolution and fail to convey spatial information Pixels

  16. Structural and Functional Imaging • Structural images have finer (smaller) pixels Pixels

  17. Structural and Functional Imaging • Brain scans (CAT, PET, MRI, fMRI) are all made up of pixels (stands for picture elements) Pixels

  18. Structural and Functional Imaging • “Slices” are assembled into “volumes” Pixels

  19. Structural and Functional Imaging • Volumes are composed of “volume elements” or voxels Voxels

  20. Structural and Functional Imaging • Another thing you want: the ability to tell other people where something is • “the activity was centered on voxel #653” will not work in a scientific journal

  21. Structural and Functional Imaging • MRI anatomical spaces • Talairach Space: • Based on detailed analysis of one elderly woman • Talairach & Tournoux (1988) • Montreal Neurological Institute Template (MNI) • based on average of 152 different brains, each normalized to Talairach space • advantage: gyri and sulci are more representative • disadvantage: it’s blurry • MNI “Representative Brain” • the one brain from the 152 in the MNI Template set that is most like the average • advantage: it’s not blurry • disadvantage: it’s still just one brain

  22. Structural and Functional Imaging • Reasons for normalizing to standard stereotaxic space (templates) • two levels: within-subject and between-subjects

  23. Structural and Functional Imaging • Within-Subject Reasons: • structural and functional volumes may not be coregistered due to • movement • distortion • results can be described in standard coordinates • data across sessions can be averaged

  24. Structural and Functional Imaging • Between-Subject Reasons: • Volumes will not match because of variability across individuals • results can be described in standard coordinates • data across participants can be averaged

  25. Preprocessing of Structural and Functional Images • Normalizing images to fit a standard template (e.g. Talairach) • Define Coordinate System using easily recognizable landmarks • Origin in the Anterior Commissure • y-axis connects AC and PC • x-axis perpendicular interhemispheric plane and through AC • z-axis perpendicular to x and y

  26. The Talairach Coordinate System PC AC

  27. The Talairach Coordinate System -y AC - PC line defines y-axis +y

  28. The Talairach Coordinate System -y -x x-axis perpendicular to interhemispheric plane +x +y

  29. The Talairach Coordinate System +z -y -x z-axis perpendicular to x-y plane +x -z +y

  30. Next time: Cortical Flattening