intersubject normalization for group analyses in fmri jody culham department of psychology...
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Intersubject Normalizationfor Group Analyses in fMRI
Jody CulhamDepartment of Psychology
University of Western Ontario
Last Update: November 29, 2008fMRI Course, Louvain, Belgium
http://www.fmri4newbies.com/
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
Talairach Coordinate System
Note: That’s TalAIRach, not TAILarach!
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
Rotate brain into ACPC plane
Find posterior commisure (PC)
Find anterior commisure (AC)
ACPC line= horizontal axis
Corpus Callosum
Fornix
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
Squish or stretch brain to fit in “shoebox” of Tal system
Deform brain into Talairach space
yAC=0 y>0y<0
ACPC=0
y>0
y<0
z
x
Extract 3 coordinates
Mark 8 points in the brain:• anterior commisure• posterior commisure• front• back• top• bottom (of temporal lobe)• left• right
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
(red > yellow > green > blue)
Source: Zilles et al., 2001, NeuroImage
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
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
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: http://www.mrc-cbu.cam.ac.uk/personal/matthew.brett/abstracts/MNITal/mniposter.pdf
Left is what?!!!
Neurologic (i.e. sensible) convention• left is left, right is right
L R
Radiologic (i.e. stupid) convention• left is right, right is left
R L
Note: Make sure you know what your magnet and software are doing before publishing left/right info!
x = 0-+
x = 0
+-
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.
Brodmann’s Areas
Brodmann (1905):Based on cytoarchitectonics: study of differences in cortical layers between areasMost common delineation of cortical areasMore recent schemes subdivide Brodmann’s areas into many smaller regionsMonkey and human Brodmann’s areas not necessarily homologous
Anatomical LocalizationSulci and Gyri
gray matter (dendrites & synapses)
white matter (axons)
FUNDUS
BA
NK
SULCUS
GY
RU
SS
ULC
US
gray
/whi
te b
orde
r
pial
sur
face
FISSURE
Source: Ludwig & Klingler, 1956, in Tamraz & Comair, 2000
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
Cortical Surfaces
segment gray-whitematter boundary
inflate cortical surface
sulci = concave = dark graygyri = convex = light gray
render cortical surface
Advantages
• surfaces are topologically more accurate
• alignment across sessions and experiments allows task comparisons
Cortical Inflation Movie
Movie: unfoldorig.mpeghttp://cogsci.ucsd.edu/~sereno/unfoldorig.mpg
Source: Marty Sereno’s web page
QuickTime™ and aYUV420 codec decompressor
are needed to see this picture.
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
Spherical Averaging
Source: Fischl et al., 1999
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.mpeghttp://cogsci.ucsd.edu/~sereno/coord1.mpg
Source: Marty Sereno’s web page
QuickTime™ and aYUV420 codec decompressor
are needed to see this picture.
