class business class website is up blackboard forum is up
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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
• Deoxygenated hemoglobin is paramagnetic - it has strong magnetic effects on surrounding molecules!
Hemoglobin
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 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 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 fMRI
• A voxel in tissue insensitive to the task demands shows random signal change
Active Rest Active Rest
60 sec 60 sec 60 sec 60 sec
Sign
al
Experimental Design in fMRI
• A voxel in tissue that responds to the task shows signal change that matches the timecourse of the stimulus
Active Rest Active Rest
60 sec 60 sec 60 sec 60 sec
Sign
al
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 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
• 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 MRI:1. Most hospitals have MRI scanners that can be
used for fMRI (PET is rare)2. Better spatial resolution in fMRI than PET3. Structural MRI is usually needed anyway4. No radioactivity in MRI5. Better temporal resolution in MRI
Advantages of PET
• Advantages of PET:1. Quiet2. A number of different molecules can be labeled
and imaged in the body
Limitations of fMRI
• All techniques have constraints and limitations
• A good scientist is careful to interpret data within those constraints
Limitations of fMRI
• Limitations of MRI and PET:1. BOLD signal change does not necessarily mean a
region was specifically engaged in a cognitive operation
2. Poor temporal resolution - depends on slow changes in blood flow
3. expensive