Neurocognitive Techniques

Question 1

What is electrical induction?

Answer 1

A moving magnetic field and an electric field induce each other, which causes measurable electric currents to flow

e.g.. in a wire

Question 2

Which technique(s) work on the basis of electrical induction?

Answer 2

MRI and fMRI

Question 3

What is the purpose of the various magnets and coils in a MRI scanner?

Answer 3

The measure and manipulate the electric and magnetic field

Question 4

On what in the body does the principle of MRI rely on?

Answer 4

Hydrogen atoms , which are the most abundant protons in the body. They are positively charged which causes them to act like spinning magnets.

Question 5

A proton is a positively charged proton, that acts like a spinning magnet.
How is this characteristic used for doing a MRI scan?

Answer 5

The net field of all protons is 0 in the body. By using an external magnetic field, the net field of protons can be changed and becomes >0. The manipulation of the proton net field is used to do MRI

Question 6

What is the technique behind a MRI scan?
Give all the steps.

Answer 6

• The magnet of the MRI scanner is an external magnetic field (B0) that causes, when turned on, the magnetic field of the protons to follow the same direction as B0, changing the net field = M0
• When another magnetic is introduced (B1), all protons can be tilted 90 degrees = temporal magnetic field.
• Then, B1 will be switched off, which causes M0 to turn around (because of the proton spinning). This causes a current in the measuring coil of the MRI scanner.
• M0 will spin back till it follows the fixed field of B0 again.
• The relative amount of signal per voxel is the contrast that is seen on a MRI scan

Question 7

What does the speed of M0 returning to original + how fast the signal decreases to 0 depend on?

Answer 7

It depends on the molecule –> so tissue type

Question 8

What is functional (f)MRI?

Answer 8

fMRI is a type of MRI that is made possible by the fact that M0 recovers more slowely in oxygenated blood than in deoxygenated blood

Question 9

What does fMRI measure?

Answer 9

It measures the dynamics between oxygenated and deoxygenated blood

Question 10

What does BOLD stand for?

Answer 10

Blood Oxygen Level Dependent

Question 11

What is a hemodynamic response in fMRI?

Answer 11

A model progression of BOLD contrast in a voxel with transient neural activity

Question 12

What can be determined by looking at the hemodynamic response? And how

Answer 12

It can determine when and how strongly a tissue was activated by correlating the measured signal with the model response.

Question 13

How can a BOLD signal be measured?

Answer 13

By comparing the activity when a stimulus is present with when no stimulus is present (baseline).

Question 14

What does BOLD measure?

Answer 14

The relative activity to the baseline –> NOT an absolute measure of activity

Question 15

Why does it take a lot of measurements to get a good BOLD signal?

Answer 15

Each scan has too much noise to get a clear contrast. So a lot of scans are necessary to reduce the SN-ratio.

Question 16

Why is it said that fMRI makes indirect measurements and what is the disadvantage of this?

Answer 16

fMRI measures the neuronal activity by measuring the blood flow. Blood flow is much slower than neural activity. So neural activity could have already happend when applying fMRI when there is a stimuli.

Question 17

What is the difference between a blocked and an event related design?

Answer 17

Blocked: Stimuli are often represented in a quick succession in blocks between baseline periods. It gives no info about duration of time course of activation
- Only simple tasks
- Multiple trials needed for good S/N-ratio

Event-related: When stimuli, the signal goes back to the baseline that gives information about duration and time course of activation is available
- Complex tasks possible
- S/N-ratio possibly worse because of net smaller signals, less trials in the same time/budget as blocked and more complex tasks have more conditions –> fewer trials per condition

Question 18

What do blobs in (f)MRI scans in research articles indicate?

Answer 18

They indicate spots with statistical differences between conditions

Question 19

What are advantages of (f)MRI?

Answer 19

• Measures whole brain activity
• Can be combined with many cognitive tasks
• Versatile: Anatomy, connectivity (DTI), metabolites (fMRS), neural activity (BOLD)

Question 20

What are disadvantages of (f)MRI?

Answer 20

• fMRI doesn’t measure neuronal acitivty but oxygen consumption (do all forms of neural activity consume same amount of oxygen? –> action vs synaptic potentials? Excitation vs inhibition?
• Only correlational –> dont know effect of measured activity
• Temporal and spatial resolution are limited
• Behavioral task is limited because of the scanner
• Expensive & time consuming (many subjects & sessions neeeded foor good signals)

Question 21

Which 2 signaltypes can be picked up in extracellular medium from electrodes?

Answer 21

• Action potentials/spikes
• Local field potentials (LFP)

Question 22

All APs of one neuron are very similar. So how is specific information encoded with spikes?

Answer 22

By the variations in the number of spikes –> spike rate, the timing and sequences of spikes

Question 23

What are LFPs?

Answer 23

A summation of transmembrane currents at one specific site of the brain

Question 24

What are sinks and sources?

Answer 24

Usually they are specific point within a signal that can show a bias.
Sinks = excitatory, sources = inhibitory

Question 25

What happens when sinks and sources occur simultaneosly within the same neuron?

Answer 25

It causes the net transmembrane current of the whole neuron to be 0

Question 26

Where are the most large and clear observable fluctuations of LFPs found?

Answer 26

From correlated inputs into brain structures where bipolar neurons are aligned in layers.
E.g. neocortex and hippocampus

Question 27

What is a non-invasive way to measure electrical activity?

Answer 27

EEG –> has high temporal resolution since it measures the summation of all measurements of the electrodes
- Difficult to interpret the signals due to distortion and attenuation

Question 28

What is an invasive way to measure electrical activity?

Answer 28

ECoG –> directly electrode measurements on the brain itself –> better signal than EEG

Question 29

What can the use of tetrodes (4 entagneld electrodes) do?

Answer 29

It can distinguish APs from different cells from each other and see if they are of the same cell-type. Multiple neurons are recorded simultaneously. It reveals spatial patterns of activation during each AP.

Question 30

What can silicon probes be used for?

Answer 30

Recording LFPs in different cortical layers. Fixed distance between recording electrodes enables studying the relationship between coritcal layers

(tetrodes can measure spike data of better quality)

Question 31

What is the disadvantage of measuring neurons electrical activity with electrodes

Answer 31

Only a limited number of neurons can be studied

Question 32

What is patch-clamp recording?

Answer 32

Recording of the membrane potential of a single neuron or the current of a single ion channel using a patch pipette

Question 33

Why can’t we combine electrical recordings with fMRI?

Answer 33

Electrodes are made of metal with is dangerous when using a fMRI scanner because of the magnets