Lecture 1 Flashcards
Introduction
What is white matter in terms of brain areas?
The neuro-connections between the different brain areas.
What is a neuron?
A special cell that can signal signals in an electrical or chemical way.
A neuron consists of a cell body and they have axons which can be very long.
Where are the cell bodies located the most?
The cell bodies are mostly in the grey matter.
How is grey matter defined?
By what we measure in an MRI.
What is white matter?
The white matter is the long axon from the cell bodies connecting all the way to other neurons.
Why is white matter white?
They are white because they have small layers of fat, myelin, around the axons. These layers of fat make sure that the electrical signal can be transferred much quicker.
What types of images does an MRI have?
- Pictures of the brain; 3D reconstructions of e.g., the cortex.
- Measures (global axonal) connections between different brain regions.
- Movies using functional MRI with which we can get an impression of the activity in the brain.
What does the abbreviation MRI stand for?
Magnetic Resonance Imaging
What does the abbreviation fMRI stand for?
Functional MRI
What can you see when looking at MRI pictures?
The brain structure.
We can make slices of the brain with MRI and we can stick them together to get a 3D construction of the structure of the brain.
What can you see when looking at fMRI pictures?
The brain function.
You get the structure and an average map of where the activity in the brain was found.
Why is it challenging to work with children when using an MRI machine?
You have to lay very still in the MRI machine.
Children have to be trained well, they will often do a mock scan, they get really good instructions and they sometimes even practice at home.
How can you do an experimental task when using an MRI machine?
There is a little mirror in the MRI machine through which they can look outside to a screen, this way they can do tasks with buttons. This way you can measure what their brain does when they’re doing an experimental task.
What kind of experiment is less practical to do when using an MRI machine?
Considering that a MRI machine is very loud, it is less practical to do an experiment with sound.
What is fMRI compared to MRI?
fMRI is a special MRI technique to measure brain activity.
What does fMRI measure?
fMRi measurements are an indirect measure of brain/neuronal activity.
We assume that if there is brain activity somewhere there is more oxygen needed which will cause more blood flow.
There is a change in hemoglobin in the red blood cells, these magnetic properties of hemoglobin is measurable.
The higher the neural activation, the higher the oxygen in the blood and the higher the fMRI signal.
What does the abbreviation of the BOLD-effect stand for?
Blood Oxygenation Level Dependent
What is something that you need to take into account when recording with an fMRI?
It takes some time because it takes some time for the blood/oxygen to go to the active areas.
So, you need to take into account that if you show a picture to a participant it will take some time before you can record activities.
What does the abbrevation EEG stand for?
Electroencephalogram
EEG (vs. fMRI)
- Non-invasive technique.
- Records brain signals.
- High temporal resolution (in ms) / Low spatial resolution.
- This is a more direct measure of electric signals, but it is more superficial. It also cannot go deep into the brain. It is also harder to locate where the signals are coming from, from which brain structures.
- You can do a very complicated analysis to get an idea of where the signal came from but in general the spatial resolution is very low and the temporal resolution is high.
- Activation during long periods of time (e.g., sleep).
- You don’t have to sit still for as long as with (f)MRI.
o So you can study children and even babies more easily. - Electrodes are placed on the outside of the scalp, you need glue to stick them on it. So afterwards you need to wash your hair very well to get the glue out.
fMRI (vs. EEG)
- Non-invasive technique
- High spatial resolution (in mm)/ Low temporal resolution (>5 sec)
o You know where the signal comes from, with high accuracy on millimeter level but it has a low temporal resolution due to the indirect measurement. - You don’t have to wash your hair afterwards.
How can you set up an experimental design if you want to measure something with fMRI?
- You have to ask yourself what brain regions are active.
- You have to have a good control condition.
- I’ts better to show images than voices.
Example: first you show a face (2500 ms), then you show a white cross (2000-5000 ms) and afterwards a picture of a house, etc.
It can take quite a long time (20-30 minutes).
Why do you need to have a good control condition when measuring something with fMRI?
The brain is always active so you can’t know if the activation is from what you want to measure or something else.
Why do you show a white cross in between images when measuring something with fMRI?
You show the white cross because it takes a little bit of time to see the brain activity you want to record that, by immediately showing the next image you can’t clearly take them apart.
What is a voxel?
One specific pixel we can map in the brain.
How can you measure the contrast between faces and houses with an fMRI?
- You contrast the brain activity between faces and houses.
- You average the signal of all of the face conditions and you average the signal of all of the house conditions and you subtract them from one another. Then you can see whether it is significantly more active when you see faces compared to when you don’t see faces.
What are the results of the measuring of faces compared to houses with fMRI?
It shows that a specific place in the brain is the Fusiform Face Area, which we know is specifically sensitive to seeing faces and face expressions.
How can you speed up the fMRI analysis?
Because it takes some time to record each slide, it will take less time to get one brain volume if you focus on a specific area in the brain.
How can you average the signal during fMRI analysis?
By alternating the slices.
In which ways can you measure a signal in slices when doing an fMRI analysis?
- Sagittal slice
- Voxel (volumetric pixel)
Sagittal slice (fMRI analysis)
- Number of slices
- Slice thickness
Voxel (fMRI analysis)
- 3D pixel from the images in the brain
- In-plane resolution
- Matrix size
- In each of these voxels you can measure the average signal. One area can be a hundred voxels wide, you can measure if all the 100 voxels are active during a certain task.
What is important to keep in mind with fMRI research?
- BOLD signal is not an absolute measure of brain activation but relative
- Control condition is thus crucial
- Many trials per condition (>20)
- Fixation between trials
- Engage participants
What is adolescence?
Growing up to be an ‘adult’; the time between childhood and adulthood.
What is the definition of adolescence (start and end)?
We define adolescence as that it starts with the onset of puberty, a biological process where you see hormone increases that will change physical characteristics.
When adolescence ends depends very much on the culture you grow up in. In some cultures you are an adult at 16, some 18, 21 or 25.
What kind of phase is adolescence?
Adolescence is a unique phase with a lot of changes in how people interact with their social environment. You often see a large shift from focus on family to focus on peers and finding their peers more important. It is often the first time people interact with romantic relationships, they learn a lot in school and there is a lot of cognitive development as well.
Does the brain between a child and adult differ much?
If you only look at what the brain looks like, the brain of a child and adult don’t differ that much in terms of size but if you look more detailed we see quite a bit of differences. Of course prenatally there is a huge difference.