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Experimental Design in fMRI

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Presentation on theme: "Experimental Design in fMRI"— Presentation transcript:

1 Experimental Design in fMRI
A real example of fMRI block design done well: alternate moving, blank and stationary visual input Moving Blank Stationary Blank 40 sec 40 sec 40 sec 40 sec

2 Experimental Design in fMRI
Voxels in Primary cortex tracked all stimuli

3 Experimental Design in fMRI
Voxels in area MT tracked only the onset of motion

4 Experimental Design in fMRI
Voxels in area MT tracked only the onset of motion How did they know to look in area MT?

5 Structural and Functional Imaging
What you really want is an image, not a squiggly line Make a map of a statistic (like t-score or z-score) that describes how well each voxel tracked the cognitive task: Set all “non-significant” voxels to be transparent

6 Structural and Functional Imaging
What you really want is an image, not a squiggly line Make a map of a statistic (like t-score or z-score) that describes how well each voxel tracked the cognitive task: Set all “non-significant” voxels to be transparent

7 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

8 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

9 Advantages of PET Advantages of PET: Quiet
A number of different molecules can be labeled and imaged in the body

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

11 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

12 Electrophysiology

13 Neurons are Electrical
Remember that Neurons have electrically charged membranes they also rapidly discharge and recharge those membranes (graded potentials and action potentials) Review relevant textbook sections if this isn’t familiar to you

14 Neurons are Electrical
Importantly, we think the electrical signals are fundamental to brain function, so it makes sense that we should try to directly measure these signals but how?

15 Subdural Grid Intracranial electrodes typically cannot be used in human studies

16 Subdural Grid Intracranial electrodes typically cannot be used in human studies It is possible to record from the cortical surface Subdural grid on surface of Human cortex

17 Electroencephalography and the Event-Related Potential
Could you measure these electric fields without inserting electrodes through the skull?


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