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Class Business . Class website is up http :// classes.uleth.ca/201003/neur3680a / Blackboard forum is up. Functional Imaging. Oxygenated hemoglobin is diamagnetic - it has no magnetic effects on surrounding molecules

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Class business

Class Business

Class website is up

http://classes.uleth.ca/201003/neur3680a/

Blackboard forum is up


Functional imaging
Functional Imaging

  • Oxygenated hemoglobin is diamagnetic - it has no magnetic effects on surrounding molecules

  • Deoxygenated hemoglobin is paramagnetic - it has strong magnetic effects on surrounding molecules!

Hemoglobin


Functional imaging1
Functional Imaging

  • blood flow overshoots baseline after a brain region is activated

  • More oxygenated blood in that region increases MR signal from that region


Experimental design in fmri
Experimental Design in fMRI

  • Experimental Design is crucial in using fMRI

  • Simplest design is called “Blocked”

    • alternates between active and “rest” conditions

Active

Rest

Active

Rest

60 sec

60 sec

60 sec

60 sec


Experimental design in fmri1
Experimental Design in fMRI

  • Experimental Design is crucial in using fMRI

  • Simplest design is called “Blocked”

    • alternates between active and “rest” conditions

Active

Rest

Active

Rest

60 sec

60 sec

60 sec

60 sec


Experimental design in fmri2
Experimental Design in fMRI

  • A voxel in tissue insensitive to the task demands shows random signal change

Signal

Active

Rest

Active

Rest

60 sec

60 sec

60 sec

60 sec


Experimental design in fmri3
Experimental Design in fMRI

  • A voxel in tissue that responds to the task shows signal change that matches the timecourse of the stimulus

Signal

Active

Rest

Active

Rest

60 sec

60 sec

60 sec

60 sec


Structural and functional imaging
Structural and Functional Imaging

  • The colour in an fMRI image indicates how well the signal at each voxel matches the pattern of active and rest blocks.


Structural and functional imaging1
Structural and Functional Imaging

  • The coregistered functional image has a “mask” so that all voxels that don’t match the stimulus pattern in time are set to be transparent…that’s why you see the anatomical image underneath


Pet another way to measure blood oxygenation
PET: another way to measure blood Oxygenation

  • Positron Emission Tomography (PET)

  • Injects a radioisotope of oxygen

  • PET scanner detects the concentration of this isotope as it decays


Advantages of fmri
Advantages of fMRI

  • Advantages of MRI:

    • Most hospitals have MRI scanners that can be used for fMRI (PET is rare)

    • Better spatial resolution in fMRI than PET

    • Structural MRI is usually needed anyway

    • No radioactivity in MRI

    • Better temporal resolution in MRI


Advantages of pet
Advantages of PET

  • Advantages of PET:

    • Quiet

    • A number of different molecules can be labeled and imaged in the body


Limitations of fmri
Limitations of fMRI

  • All techniques have constraints and limitations

  • A good scientist is careful to interpret data within those constraints


Limitations of fmri1
Limitations of fMRI

  • Limitations of MRI and PET:

    • BOLD signal change does not necessarily mean a region was specifically engaged in a cognitive operation

    • Poor temporal resolution - depends on slow changes in blood flow

    • expensive