Anatomy

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 -gt Lobes -gt 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? Whats 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 its blurry
• MNI Representative Brain
• the one brain from the 152 in the MNI Template
  set that is most like the average
• advantage its not blurry
• disadvantage its 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