Neuroimaging Methods 2 Flashcards
What is EEG and how does it work?
Electroencephalography
The positively and negatively charged ions in our brain create a voltage
This transfers information within or between neurons (e.g. EPSP or IPSP)
Measure these charged ions inside and outside the cell membrane
We measure these because action potentials have much smaller activity compared to postsynaptic potentials
What is spatial and temporal summation?
Spatial - measuring lots of active neurons at once, as there is a larger postsynaptic neuron activation when lots of neurons are activated at the same time in comparison to just one
Temporal - we look at the activity of a single neuron that fires very fast over a period of time
Under what conditions can EEG measure postsynaptic potentials?
When the neurons are in open field configuration
This means they all point in the same direction as it creates a larger electric field
Closed field configuration is when they cancel each other out by pointing in different directions
EEG measures mostly radially oriented neurons (perpendicular to the skull)
What are we looking for when we measure activity using EEG?
Event-related potentials (ERP)
ERPs are time locked to a specific activity
This is because we continuously record everything over time while performing cognitive tasks
Not interested in the background activity
How do we find the ERP when using EEG?
We repeat the event to elicit the same brain response
We then average the brain activity together
Averaging noise will cancel it out
Averaging the ERP gets it more accurate
So after averaging we’re left with just the ERP
What are some assumptions we have when using the averaging technique?
The signal is time locked to the event
The background noise varies randomly
The repetition of the same event will elicit the same brain response (priming might influence this)
What are the pros and cons of EEG?
Pros - excellent temporal resolution as we are directly measuring neural activity compared to just blood flow
Cons - poor spatial resolution as we can only measure the activity close to the scalp that is open field
What is the N170 component?
It is the ERP associated with encoding faces
Stands for negative peaks around 170ms after a stimuli is presented
N170 specifically large when shown faces
What is the N400 component?
It is the ERP associated with language comprehension
Participants were presented with a sentence and a final word that did or did not match
Find a larger activity at 400ms if the final word didn’t match compared to if it did
What did ERP tell us about subsequent memory recall?
Participants did a classic memory task - presented with words they had to learn (encoding phase) and then had a memory test (retrieval phase)
The words that were remembered had larger positive ERPs in the encoding phase compared to forgotten words
Showed a higher probability for specific words being remembered
What do ERPs tell us about free will?
Tried to find the relationship between neural activity (action planning) and the intention to act
In an experiment it was found that the brain’s decision to act was 500ms before the action, but the conscious intention was only 200ms before
Therefore free will can stop an action but does not initiate it
What is MEG and how does it work?
Magento-encephalography
Measures magnetic activity
The activity it measures is tangential (parallel) to the skull so it is complimentary to EEG
What is SQUID?
Superconducting Quantum Interference Devices
These are magnetometers used in MEG to measure small magnetic fields
Kept in liquid helium
What are the pros and cons of MEG?
Pros - high temporal resolution and magnetic fields are not affected by brain tissue
Cons - very expensive and is affected by magnetic artefacts (like a bus going by outside)
What is NIRS and how does it work?
Near Infrared Spectroscopy (also known as optical imaging)
Light is shone into tissue to see if it passes through
Different wavelengths are better at penetrating than others (e.g. infrared better at passing through than ultraviolet)
