Brain Imaging and Emotion Methods

Question 1

What is PET

Answer 1

positron emission tomography

Question 2

define a PET

Answer 2

position = positvely-charged radioactive partical.
PET involves injecting positron-emitting compound into the bloodstream.
as radio-labeled compound decays, positrons are emitted. Positrons travel a short distance (0-5mm) before colliding with an electron. This annihilation event emits a gamma ray
scanner can measure concentration of compound within a particular region by counting gamma rays.

Question 3

What physical signal does the PET scanner detect

Answer 3

PET scan can be used to measure the density of NT related protein in specific areas

Question 4

What is the difference between a priori and post hoc analysis?

Answer 4

a priori is guided by a particular hypothesis about what parts of the brain are expected to be activated by what taks
a post hoc is not guided by this particular hypothesis

Question 5

Why does one require a higher statistical threshold than the other (eg: p < 0.0001 vs p <0.1?)

Answer 5

Post hoc requires p < 0.0001 means that less than 1 out of 10000 tests will produce a significant value by chance, but with this threshold, a dataset of 500K voxels could produce 500 “activated” voxels by change.

They must adapt the threshold to a number of statistical comparisons made on the data set.

Question 6

What’s the difference between region of interest (ROI) and whole brain analysis?

Answer 6

ROI has a hypothesis regarding localization of function.

Whole Brain Analysis (aka voxelwise)

• when t-tests are done for all voxels of the brain.
• BOLD signal at each voxel is averaged across all participants for each condition separately.
• the t-test is one to contrast the experimental and control conditions.

ROI (Region of Interest)

• experimenter has a hypothesis about localization of brain function
• contrasts BOLD signal in a set of voxels that defines the ROI.

Question 7

The two radioactive tracers used in PET scans measure two types of neural activity. They are:

Answer 7

increased blood flow
or
glucose uptake

Question 8

What can PET do that fMRI can’t?

Answer 8

PET can be used to measure the density of NT-related proteins in specific brain areas.

Question 9

Why is brain activity mostly measures by fMRI compared to PET?

Answer 9

• fMRI is non-invasive
• fMRI has better spatial resolution
• fMRI is “easier” and less expensive (it doesn’t require a nearby cyclotron to produce positron-emitting compounds)

Question 10

What is the goal of fMRI study?

Answer 10

localization of function

Question 11

PET and fMRI led to the development of a new field called

Answer 11

cognitive neuroscience

Question 12

What physical signal is detected by the fMRI scanner?

Answer 12

Oxygen content of venous blood (produces difference in the magnetic resonance signal)

Question 13

What is the purpose of spatial normalization and how is it done?

Answer 13

The purpose of spatial normalization is to get an average fMRI result across subjects.
The fMRI image of each brain is transformed so that superficial structures line up to match a standard template.

Question 14

What is a voxel cluster and how is it used?

Answer 14

voxel: unit of brain scape used in fMRI data anylysis (volume + pixel).
A voxel cluster is a bunch of voxels that are adjacent to one another. A voxel cluster is defined such that within a group of contiguous voxels, a BOLD signal in each voxel differs between control and experimental conditions by an amount that exceeds a statistical threshold (P < 0.0001)

It can be used so that researchers can limit their focus to regions of interest.

Question 15

What do the colored blods positioned on high resolution MRI images of brain slices represent?

Answer 15

The colors represent the mean difference between conditions at that location as a t, z, or p value. (stereotaxic coordinates)

Question 16

What are 3 other ways of describing the locations of areas of activation or deactivation?

Answer 16

• name of the brain
• statistical parameter map (blocks)
• Brodmann Area number (cortical area)

Question 17

What % difference in the BOLD signal typically produces statistically significant results for a given voxel cluster?

Answer 17

0-4%

• even small changes can be statistically significant if they are consistent
  - its positive to have this although the magnitude of change in small.

Question 18

How is it possible that an increase in the BOLD signal can correspond to either increases or decreases in the firing of the projection neurons?

Answer 18

BOLD depends most on the activity of afferents, rather than the firing of efferent (projection) neurons
- afferent activity includes both excititory and inhibitory activity involving afferents and interneurons.

Question 19

Briefly describe the types of changes in neural activity that could contrivute to findings of activation in fMRI study

Question 20

Briefly describe two changes in neural activity that could contribute to finding reas of deactivation in an fMRI study

Answer 20

• decrease in local CBF response
• decrease in target cell spiking activity (output)

Decrease in BOLD signal shows neuronal deactivation.

Question 21

BOLD

Answer 21

Blood oxygen level dependent.
Since blood ocygen oygenation varies according to the level of neural activity, these difference can be used to detect brain activity.
BOLD imaging is an indirect measure of neural activity.

Question 22

ROI

Answer 22

Region of Interest.

A ROI analysis constrasts BOLD signal in a set of voxels that defines the ROI

Question 23

Type I Error

Answer 23

rejecting the null hypothesis when it should be accepted.

• ie; when there is no real difference between control and experimental groups
• gives false positive results

Question 24

Type II Error

Answer 24

accepting the null hypothesis when there is a real difference between conditions/groups.
- gives false negative results

Question 25

voxel cluster

Answer 25

a bunch of voxels that are adjacent from one another

Question 26

Brodmann Area

Answer 26

a region of the cerebral cortex defined by its cytoarchitecture or histological structure and organization of cells.

Question 27

What does BOLD signal measure fMRI measures changes in?

Answer 27

Synaptic activity (excitation and inhibition)