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Presentation on theme: "Class Business Class website is up Blackboard forum is up."— Presentation transcript:

1 Class Business Class website is up Blackboard forum is up

2 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

3 Functional Imaging blood flow overshoots baseline after a brain region is activated More oxygenated blood in that region increases MR signal from that region

4 Experimental Design in fMRI Experimental Design is crucial in using fMRI Simplest design is called Blocked – alternates between active and rest conditions ActiveRestActiveRest 60 sec

5 Experimental Design in fMRI Experimental Design is crucial in using fMRI Simplest design is called Blocked – alternates between active and rest conditions ActiveRestActiveRest 60 sec

6 Experimental Design in fMRI A voxel in tissue insensitive to the task demands shows random signal change ActiveRestActiveRest 60 sec Signal

7 Experimental Design in fMRI A voxel in tissue that responds to the task shows signal change that matches the timecourse of the stimulus ActiveRestActiveRest 60 sec Signal

8 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.

9 Structural and Functional Imaging The coregistered functional image has a mask so that all voxels that dont match the stimulus pattern in time are set to be transparent…thats why you see the anatomical image underneath

10 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

11 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 PET 3.Structural MRI is usually needed anyway 4.No radioactivity in MRI 5.Better temporal resolution in MRI

12 Advantages of PET Advantages of PET: 1.Quiet 2.A number of different molecules can be labeled and imaged in the body

13 Limitations of fMRI All techniques have constraints and limitations A good scientist is careful to interpret data within those constraints

14 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


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