1. Intersubject Normalization for Group Analyses in fMRI
Jody Culham
Department of Psychology
University of Western Ontario
Intersubject Normalization for Group Analyses in fMRI
Last Update: November 29, 2008
fMRI Course, Louvain, Belgium

2. Brains are Heterogeneous
Slide from Duke course

3. How can we define regions?
Talairach coordinates
Example: The FFA is at x = 40, y = -55, z = -10
Anatomical localization
Example: The FFA is in the right fusiform gyrus at the level of the occipitotemporal junction
Functional localization
Example: The FFA includes all voxels around the fusiform gyrus that are activated by the comparison between faces and objects
Kanwisher, McDermott & Chun,
1997, J Neurosci

4. Talairach Coordinate System
Talairach & Tournoux, 1988
made an atlas based on one brain
any brain can be squished or stretched to fit hers and locations can be described using a 3D coordinate system (x, y, z)
… from an alcoholic old lady
Note: That’s TalAIRach, not TAILarach!

5. Rotate brain into ACPC plane
Find anterior commisure (AC)
Corpus Callosum
Fornix
Find posterior commisure (PC)
ACPC line
= horizontal axis
Pineal Body
“bent asparagus”
Note: official Tal says to use top of AC and bottom of PC but I suspect few people actually do this
Source: Duvernoy, 1999

6. Deform brain into Talairach space
Mark 8 points in the brain:
anterior commisure
posterior commisure
front
back
top
bottom (of temporal lobe)
left
right
Squish or stretch brain to fit in “shoebox” of Tal system
ACPC=0
y>0
y<0 z y
AC=0
y>0
y<0 x
Extract 3 coordinates

7. Do We need a Tarailalch Atras?
Variability between Japanese
and European brains, both male
(red > yellow > green > blue)
Variability between male and female brains, both European
Source: Zilles et al., 2001, NeuroImage

8. Smoothing and Averaging
Large activations across multiple subjects are more likely to show common activation than small ones
-->
Need to smooth (esp. for RFX analyses)
UNDER CONSTRUCTION: Need to make a slide that shows this with real data

9. Talairach Pros and Cons
Advantages
widespread system
allows averaging of fMRI data between subjects
allows researchers to compare activation foci
relatively easy to use
Disadvantages
not appropriate for all brains (e.g., Japanese brains don’t fit well)
activation foci can vary considerably – other landmarks like sulci may be more reliable

10. MNI Space
Researchers at the Montreal Neurological Institute created a better template based on a morphed average of hundreds of brains (not just one brain like Talairach)
The MNI brain is more representative of average brain shape; however, it does not provide Brodmann areas
The MNI alignment is more complex than Talairach: SPM uses it but many software packages still use Talairach
CAVEAT: The MNI and Talairach coordinate are similar but not identical -- careful comparison requires a transformation
Source:

11. Left is what?!!! L R R L Neurologic (i.e. sensible) convention
left is left, right is right L R
x = 0 - +
Note: Make sure you know what your magnet and software are doing before publishing left/right info!
Radiologic (i.e. stupid) convention
left is right, right is left R L
Note: If you’re really unsure which side is which, tape a vitamin E capsule to the one side of the subject’s head. It will show up on the anatomical image.

12. Brodmann’s Areas Brodmann (1905):
Based on cytoarchitectonics: study of differences in cortical layers between areas
Most common delineation of cortical areas
More recent schemes subdivide Brodmann’s areas into many smaller regions
Monkey and human Brodmann’s areas not necessarily homologous

13. Anatomical Localization Sulci and Gyri
gray matter
(dendrites & synapses)
white matter
(axons)
FUNDUS
BANK
GYRUS
SULCUS
pial surface
gray/white border
SULCUS
FISSURE
GYRUS
Source: Ludwig & Klingler, 1956,
in Tamraz & Comair, 2000

14. Variability of Sulci
Source: Szikla et al., 1977, in Tamraz & Comair, 2000

15. Variability of Functional Areas
Watson et al., 1995
- motion-selective area, MT+ (=V5) is quite variable in stereotaxic space
however, the area is quite consistent in its location relative to sulci
junction of inferior temporal sulcus and lateral occipital sulcus
see also Dumoulin et al., 2000

16. Cortical Surfaces Advantages surfaces are topologically more accurate
segment gray-white
matter boundary
render cortical surface
inflate cortical surface
sulci = concave = dark gray
gyri = convex = light gray
Advantages
surfaces are topologically more accurate
alignment across sessions and experiments allows task comparisons

17. Cortical Inflation Movie
Movie: unfoldorig.mpeg
Source: Marty Sereno’s web page

18. Cortical Flattening Source: Brain Voyager Getting Started Guide
2) make cuts along the medial surface
(Note, one cut typically goes along the fundus of the calcarine sulcus though in this example the cut was placed below)
1) inflate the brain
3) unfold the medial surface so the cortical surface lies flat
4) correct for the distortions so that the true cortical distances are preseved
Source: Brain Voyager Getting Started Guide

19. Spherical Averaging
Future directions of fMRI: Use cortical surface mapping coordinates
Inflate the brain into a sphere
Use sulci and/or functional areas to match subject’s data to template
Cite “latitude” & “longitude” of spherical coordinates
Movie: brain2ellipse.mpeg
Source: Marty Sereno’s web page
Source: Fischl et al., 1999

20. Spherical Averaging
Source: MIT HST583 online course notes