Psyc 441: lecture 10 (functional brain changes in sz – Part 1)

Question 1

What is Functional magnetic resonance imaging (fMRI)?

Answer 1

1) Uses a very strong magnetic field to measure blood flow in the brain
2) Non-invasive, can do many different cognitive tasks

Question 2

What is a standard space?

Answer 2

These pictures are taken in what we call slices and these are stacked together to make a box that covers the whole brain. You get a 3D image of the brain. Then you put these scans in a standard space. when we want to have a comparison, you need to put them in the same box (i.e male brain compared to each other). It means you can overlap structural and functional scans.

Question 3

What is the purpose of combining structural and functional scans?

Answer 3

• In a PET and fMRI scan, it is difficult to see where in the brain the most activity is happening. Therefore, when you overlap these scans to a structural MRI, you can fill in the blanks.

Question 4

In other words, a functional scan is made of _____. Therefore a standard space means that all voxels are in ___________ for all brains. And we can overlap ______ and functional scans.

Answer 4

In other words:

• Functional scans made up of voxels
• Standard space means that all voxels are in (relatively) the same location for all brains
• Can overlap structural and functional scan

Question 5

fMRI: How does it work?

Answer 5

An fMRI measures -blood flow to different parts of the brain by measuring changes in changes in blood oxygen (O2). Here’s how it works:

1) O2 is carried on hemoglobin, which is paramagnetic. (has magnetic properties).
2) The magnetic properties of hemoglobin are different when going to cells (oxygenated) than when flowing away from cells (deoxygenated).
3) The most active parts of the brain will have greatest changes in O2 level, i.e. greatest contrast between deoxy- and oxy- hemoglobin.
[change between oxy and de-oxy is the contrast measured]

Question 6

What does BOLD stand for?

Answer 6

BOLD: Blood oxygen-level dependant contrast = most common measure of brain activity.

Question 7

What is the difference between fMRI and PET scans?

Answer 7

fMRI require a comparison between conditions.

For fMRIs, all experiments based on a comparison between:

1) baseline condition
2) active or experimental condition
3) between two groups.

Question 8

Explain the Task comparison or “Cognitive Subtraction” (Experimental Design for PET and fMRI).

By comparing brain activity during two tasks that differ by only one cognitive component, _____________

Answer 8

we can isolate brain activity related to that component.

i.e. brain regions active in color vision

Question 9

In the type of experimental design “Cognitive Subtraction”, what would be a third variable not accounted for? To account for a third variable in a Task comparison or “Cognitive Subtraction”, what are the steps you should take?

Answer 9

Brain regions active in emotional response to the content depicted in the picture, (e.g.remembering a trip)

• Be sure that test and baseline conditions are closely matched
• Examine blood flow changes only in specific regions during performance of the task
• Look at blood flow correlated to behavioral measures of a task
• Patient groups and controls must be well matched.

Question 10

What were the findings of the Hallucinations and auditory cortex (Dierks, 1999) study?

Hint: very first study looking at whether you could identify activity in the brain when SZ were experiencing auditory hallucinations.

Condition 1:
They asked patients to push a button when they were experiencing a hallucination.

Condition 2:

They played people sounds (Speech, reversed speech and tones). They wanted to see if brain activity would be similar both during hallucinations and sounds.

Answer 10

• Similar activation in auditory cortex for hallucinations as for sounds
• From other studies, we know that activity in auditory cortex is decreased during inner speech (i.e., talking to yourself)
• Because hallucinations generate activity in auditory cortex that is similar to real sounds, hallucinations are experienced as real

Conclusion: - SZ patients experience auditory hallucinations as real external sounds.

Question 11

Why is activity in auditory cortex decreased during inner speech?

Answer 11

• When we speak, motor cortex lets auditory cortex know (corollary discharge)
• This reduces activity in auditory cortex [This lets us know that we are speaking, not someone else] we don’t confused inner speech with external speech of someone else
• This also happens when we just imagine speaking (inner speech or talking to ourselves)
• So, if activity in auditory cortex is the same for hallucinations and external sounds (including speech) then people with SZ don’t have the signal that the sound is internal. something is faulty

Question 12

In terms of cognitive tasks, we know that people with SZ have problems in ____________

Answer 12

attention

Question 13

What were the results of the Continuous Performance Task (CPT)?

Standard version:

• Hit the key when you see the X
• Number of Xs can vary

A-X CPT

• Hit the key when you see the X only if there was an A before it

Answer 13

• No problems for the simple version

- More difficult for the A-X version

Question 14

Which region of the brain is associated with the A-X CPT cognitive task?

Answer 14

The dorso-lateral prefrontal cortex (DLPFC)

Question 15

What is the role for the dorso-lateral prefrontal cortex (DLPFC)?

Answer 15

• important for maintaining rules,
• important for executive function,
• associated with WCST.
• The DLPFC is involved in executive functioning and control of cognitive processes [science direct article]

Question 16

Results often show ______ activity in dorso-lateral prefrontal cortex (DLPFC) in SZ, but not all of them

Answer 16

decreased

Question 17

What was the methodology and findings of the A-x cpt and medication naïve sz patients (Barch, 2001) study as discussed in class [what is exactly on the slide]

Answer 17

1) A-X CPT – but also included short and long delay
1st episode patients who have never taken medication

2) Controls and people with SZ show similar activity for short delay
3) Controls showed greater DLPFC activity for long delays, people with SZ did not
4) So, attention/DLPFC function may be normal when the task is relatively simple, but cannot recruit further resources when task gets harder

May also be that early in the disorder DLPFC dysfunction is less

Question 18

What was the methodology and main findings of the A-x cpt and errors in SZ (carter, 2001) study [as discussed on the slide]

Answer 18

• A-X CPT
  Scanned at four points before (T5 and T6) and after (T7 and T8) an error
• Controls and SZ show similar activity for correct responses
• Controls showed increased activity in the anterior cingulate cortex following errors; patients with SZ did not
• ACC is associated with error detection and correction

In other words:

• They looked at particular errors in the A-x CPT tasks
• scanned the brains continuously (10-15 mins) and looked at 4 different time points
• 2 times points right before and right after the error ( so what is the brain doing before you make a mistake and after you make a mistake)
• When controls and SZ made no mistake showed similar activity at these time points.
• When controls made an error there was a big increase in the ACC
• But SZ showed a decrease in ACC
• Remember the ACC is associated with error detection and correction