Cognitive Neuroscience Flashcards
What process is performed by the myelin sheath of a neuron?
Insulates the axon and maintains the speed of communication of neural impulses
EEG signals are produced by ______ synchronisation of cortical field activity and are measures as changes in ______, recorded at the scalp
Partial, voltage
What is an advantage of fMRI?
structural data can be acquired in the same session
Working with data from individuals with brain damage is known as…
Neuropsychology
What technique causes a delay of around 4 seconds between brain activity and response detection?
fMRI
What does EEG enable us to assess?
The precise timing of neural activation
What is the region located at the back of the brain that processes visual information?
Visual cortex
The BOLD signal detects how much _______ is in a brain region
Oxygen
What is an disadvantage of MEG?
Cost £
SAQ: how do we know when are where face processing occurs in the brain?
-Using EEG
- each visual change= an event/stimulus onset
- neurons are responding to this stimulus onset
- Electrodes put on head by 10 20 system, electrodes have numbers on them= universal system used to place
- electrodes w odd numbers = on the left, electrodes w even = on the right
= if image on right hand of screen= would see very strongly on left hemisphere at back of the head
SAQ: What does an Event Related Potential (ERP) measure? Provide an example of an ERP study that has told us something about a cognitive mechanism
- ERP measures a change in electrical activity
- its the average of many single trial epochs
- if signal is clear and strong= see a response to stimulus
e.g. N170 - electrodes over partial area= signal changes depending on what you see
between 100 and 200ms = process facial info a lot stronger than other images, call this strong response to faces in these regions at this particular time N170 - difference between if face is upright or inverted
- if upright= process it earlier than inverted
- told us when processing faces we use N170= in the ‘sts’ part of brain
What is the link between cognitive psychology and neuroscience?
- Cog= trying to understand the process of cognition
- Neuroscience= biological processes, scientific study of the nervous system, structure of the nervous system
THE LINK THEREFORE: - how brain structures and processes mediate cognitive behaviour
What does cognitive neuroscience tell us ?
Where in the brain things are happening, how the processes work, how the neural networks work, how info travels around the brain
What can EPRs tell us ?
Where and when processing happens in the brain
What is VEP?
Visual Evoked Potential
= a specific type of Event Related Potential that is a neural response to the presentation of a visual stimulus
= therefore the VEP is a ERP
Is fMRI a direct measure of brain activity?
No- which is a disadvantage
- A direct measure would measure the activity itself e.g. a single electrode recording would directly measure the neural firing associated with a particular aspect of cognition
- fMRI measures a physiological response to the brain activity i.e. after the activity happens there is a 4s delay before oxygenated blood flows back to the region where the brain activity took place
- Then work backwards to try and infer what brain activity has caused the signals detected = the inverse problem
How is are electrodes set up in EEG?
Electrodes containing odd numbers will be placed over the left hemisphere and electrodes with even numbers will be placed over the right hemisphere
What is N170?
- happens at 170ms after stimulus onset
Why is EEG and fMRI used for N170?
Because fMRI can identify a location of processing via the BOLD response but takes around 4s to appear
The N170 happens at 170ms after stimulus onset so fMRI cant measure directly
- THEREFORE use EEG as well as fMRI
How do we find out about the brain structure?
Autopsy, structural magnetic resonance imaging (MRI)
How do we find out about brain function?
Scalp- located electrodes = in EEG and ERPs, fMRI, MEG, TMS,PET
How do we investigate Neuropsychology?
Data from individuals with brain damage
What is fMRI?
Functional magnetic resonance imaging
- Neurons are active and burn energy, and are automatically replenished via blood after a few s
- Blood contains haemoglobin (which contains iron) so it’s possible to detect blood flow= can distinguish between o2 rich and o2 depleted blood
- Measure the BOLD (blood o2 level dependent) response in the scanner= can work out what parts of the brain were recently active
What are the advantages of fMRI?
- Tells us which parts of the brain are used in task
- Reasonable temporal resolution = 4s
- Get structural data within same session
What are the disadvantages of fMRI?
- Claustrophobic, noisey, movement artifacts (difficult for button presses)
- Can’t have any metal based equipment for stimulus present
- BOLD isn’t a direct measure of activity, and care should be taken interpreting it
What is TMS?
Transcranial Magnetic Stimulaton
- uses large portable magnet placed next to the head
What is TMS?
Transcranial Magnetic Stimulation
- uses large portable magnet placed next to the head
- magnet turned on would interfere with the function of your brain in particular regions
- non-invasive method causing depolarization or hyperpolarisation of neurons in the brain i.e. increase/decrease activity
- can be seen via twitched in limbs= used motor evoked potential
- uses electromagnetic induction to induce weak electric currents in the cortex
(invented at sheff uni )
What can TMS produce?
A simulated temporary ‘lesion’ (for a few s) of the brain region by preventing normal function of that region. Thought to be without any long-lasting (adverse) effects
What are the advantages of TMS?
- Near portable
- Can ‘stimulate’ or ‘lesion’
What are the disadvantages of TMS?
- Difficult to specify precise regions
- Only surface regions- cant look at function in the midbrain
What is MEG?
Magnetoencephalogram
- The pyramidal cells (pyramidal neurons) of the cortex, when active, generate a significant magnetic field
- MEG records these magnetic fields
- Magnetic fields are less distorted by the scalp than electric fields (which we use to measure EEG)
What does EEG and MEG need?
- For EEG and MEG need to have synchronous firing of 10,000s neurons to produce a field which is large enough to measure, they all need to be working together
What are the advantages of MEG?
- Excellent temporal resolution
- Good spatial resolution (not distorted by the scalp and for whole brain) especially if combined with MRI
What are the disadvantages of MEG?
- Cost £££££££££
- The inverse problem for finding what causes what = not a direct measure of the activity
What is EEG?
Electroencephalography
- Measures electrical signals generated by the brain through electrodes placed at the scalp
- EEG signals are produced by partial synchronisation of cortical field activity and are measured as changes in voltage, recorded at the scalp, over time
- Electrodes placed on scalp, connected with gel or conductive solution
- The amplifier measures the difference in voltage between the active electrode and a reference electrode
How are the electrodes positioned on the scalp ?
By the 10-20 system, electrodes have numbers on, electrodes containing odd numbers will be placed over the left hemisphere and electrodes with even numbers will be placed over the right hemisphere
What are the advantages of EEG?
- Good temporal resolution
-Less subject to motion artifacts, not claustrophobic, can be used even by infants.
Major artifact= eyes blink- but can be eliminated automatically via monitoring eyelid
What are the disadvantages of EEG?
- Weak spatial resolution
- Inverse problem- given a pattern of activity, how do you determine which brain regions caused it? = by signal processes = can be quite complex
What is ERP?
Event related potential
= the average of many single trial epochs
- Event= stimulus
- Related= how links
- Potential= as measuring a change in electrical activity
- If signal is clear and strong= see response to stimulus
What is N170?
- Electrodes over partial area
- between 100 and 200ms = processing facial images a lot more strongly than the other images
- Call this strong response to faces in these regions at this particular time N170= an ERP component
- Can show the difference between if a face is upright or inverted
- If upright= process it earlier
- Uses combined EEG and fMRI analysis to understand where things are happening in the brain and when they are happening
- When processing faces = done in the STS part of brain
How do we know where early visual processing and face processing occur in the brain?
- From fMRI scans, we know that early visual processing occurs in the primary visual cortex right at the back of the brain
- = can see clearly from scans
- fMRI images= take images throughout height of the brain, can see that activity is strongest half way up = red
- Each visual change = an event/stimulus onset
- Neurons are responding to this stimulus onset, responding quickly
- Left checkerboard= right hand brain at back
- Electrodes w odd nos on the left, electrodes with even nos = on the right
- If image on right hand screen= would see v strongly on left hemisphere at back of the head
= observing the visual evoked potential
Why is it hard to get brain signals?
Because of the noise= like needle in a haystack
- Need to filter out all other things the brain is doing to get cognitive process
How many neurons are in 1 cubic mm of the brain?
1 million neurons in 1 cubic mm of
Is everyone’s brain structure and brain functioning the same?
There are individual differences of structure and function- just as all our faces are different, all brains are different
What influences the structure of the brain?
Experience, individual variability, genetics
Are brains symmetrical?
Not entirely
What types of individual differences can affect brain functioning?
The way we perform cognitive functions can vary from day to day e.g. influenced by strategy, mood, task difficulty
