Lecture 7: Methods to Study the White Matter

Question 1

Name all the methods to study white matter

Answer 1

• Dissection
• Injection of tracers in a specific cortical area
• Diffusion Imaging Tractography (dMRI)

Question 2

Dissections

Answer 2

• Post-mortem
• Pros:
• Cons:
  
  • Hard to see where the axons start and terminate
• Important notes:
  
  • Dejerine identified arching white matter tract: arcuate

Question 3

Injection of tracer in a specific cortical area

Answer 3

• Participants: Living macaque monkey studies (not humans)
• Usage:
  
  • Study anatomical connections
  • See the exact termination and course of the axons
• Pros:
  
  • Indicate direct connectivity
• Cons: na
• Important notes:
  
  • Types:
    
    • anterograde
      
      • From soma to dendrites
    • retrograde
      
      • From dendrites to soma

Question 4

Diffusion Image Tractography

Answer 4

• Participants: Living humans
• Usage: reconstruct or virtually dissect white matter tracts in vivo
• Pros:
  
  • in vivo
  • Useful to have anatomical priors
• Cons:
  
  • not exact method to find out where fibres go or which brain areas are anatomically connected
    
    • Limitations:
      
      • crossing fibres
      • parallel tracts within same white matter area
      • Cannot detect if there is a synapse
• Important notes:
  
  • dMRI:
    
    • water diffusion along the axons

Question 5

Give a research example where they use diffusion tractography

Answer 5

• Language tracts
  
  • Specifically the arcuate fasciculus which connects Broca’s area to Wernicke’s area
  • Studied and reconstructed many times using dMRI

Question 6

dMRI is a very limited technique, which errors could come up?

Answer 6

• Mixing up tracts
  
  • ex: AF and MLF or AF and SLF

Question 7

One error that might come up using dMRI is to mix up the tracts, how was AF and SLF differentiated?

Answer 7

• Based on what is know:
  
  • injection of tracers in macaque monkeys showed that SLF has 2 branches
  • landmarks
• This allowed to separate SLF 2 and 3
• Research allowed us to better understand and define the functional role of each of those tracts in human congnition

Question 8

how can we use anatomical landmarks to separate SLF II and III?

Answer 8

• Goal:
  
  • restrict the tract from frontal to:
    
    • supramarginal gyrus
    • angular gyrus
    • posterior temporal

Question 9

What is another way to separate SLF II and SLF III?

Answer 9

• We can combine resting-state:

Question 10

How can we identify the different landmarks?

Answer 10

• By identifying the sulci and gyri
• Another way is by using MNI coordinates

Question 11

DWI Tractography

Answer 11

• Can detect true or false connections