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methods of cognitive neuroscience > Task 3 > Flashcards

Task 3 Flashcards

1
Q

What is an EEG?

A
  • Electorcenphalography
  • records the overall brain activity continuously
  • includes endogenous changes in electrical activity as well as changes triggered by events
  • signal from each electrode is amplified
  • measures the voltage between two electrodes (active + reference)

+ EEG patterns change through processes (but in a predictable manner)
+ normal EEG patterns are well known -> allows detection of abnormal activity
- insights from EEG are limited because recordings represent the brain´s global activity

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2
Q

where are the electrodes placed in EEG?

A
  • electrodes can measure the sum of charges in their surrounding
  • only, when they are close to either side of the dipole
  • when the electrodes are equally far away from both dipoles, they measure a net neutral
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3
Q

What is special about the EEG electrodes?

A
  • measure the activity of large populations of neurons, when active together
  • electrodes meaasure the difference in voltage between the recording electrode and the reference electrode
  • voltage can be measured on the outside, because tissue of the brain, skull and scalp passively conduct electrical currents
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4
Q

What is spatial resolution

A
  • where in the brain is the activity happening
  • is a clear image possible
  • how clear is the structure of the brain depicted
  • how detailed can activity be allocated?
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5
Q

What is temporal resolution?

A
  • how long does it take to see the image effect?
  • if an image takes a couple of seconds, the temporal resolution is bad
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6
Q

What kind of spatial + temporal resolution does EEG have?

A

Spatial: quite low: on the order of a few cm3

Temporal: High (ms or better)

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7
Q

What are the neural origins of EEG?

A
  • arises from synchronised synaptic activity in populations of cortical neurons
  • extracts ERP
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8
Q

What are postsynaptic potentials?

A
  • PSPs
  • origin of ERPS (event-related-potentials), which occur during neurotransmission when the binding of neurotransmitters to receptors change the flow of ions across the cel membrane
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9
Q

What are dipoles?

A
  • A region of positive charge (= source) separated from a region of negative charge (= sink)
  • the sum of many individual dipoles (= neurons) in an area is measurable as a single dipole
  • the magnitude of the dipole reflects the number of neurons, whose dipoles are summing together
  • in order for a measurement ≠ 0
    > parallel
    > synchronously active (to achieve net charge)
  • polarity of the signal measure depends on the dipole´s orientation
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10
Q

What are radial dipoles?

A
  • oriented vertical to the scalp surface
  • produce deflections in roughly one direction
  • I
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11
Q

What are tangential dipoles?

A
  • oriented parallely to the scalp surface
  • produce deflections in both directions
  • __
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12
Q

what is Volume conduction?

A

a pool of ions repels nearby ions of the same charge, resulting in a wave of change that travels through the extracellular space

-> how EEG travels within the brain

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13
Q

What is ECOG?

A
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14
Q

What is the signal to noise ratio?

A

measure of how much signal the system measures, compared to how much noise is measured

-> higher SNR refelcts a better quality signal that is contaminated by less noise

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15
Q

What are sources of noise?

A
  • external noise: influences the measurement prooportionally to their distance from the electrodess (EEG sytsems may solve the problem of external noise through - passive shielding - active electrodes)
  • internal noise: arises within the body and thus cannot be eliminated during data collection (might be minimised by controlling environmental factors and participant behaviour -> filtering and artefact detection)
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16
Q

What are artifacts?

A
  • artifacts influence the outcome -> confounder (= noise)
  • artefact detection is applied post processing to filter out internal noise
  • examples: eye movements, eye blinks
  • solution: instruct participants to maintain fixation and minimise eye blinks (! might distract from task and change brain activity)
17
Q

What are ERPs?

A
  • ERP graphs show the average of EEG waves time-locked to specific events
  • useful for:
    > Answering questions about the timing of mental processes
    > Determining which cognitive processes are influenced by experimental manipulation
    > assessing the anticipatory processes that occur before a stimulus
    > covertly monitoring mental activity in the absence of a behavioural response
18
Q

what are the major ERP components?

A
  • exogenous components: triggered by a stimulus and may be modulated by top-down processes
  • endogenous components: neural processes that are entirely task dependent
  • motor components: accompany the preparation and execution of a motor response
19
Q

What are endogenous ERP components?

A
  • the most common endogenous ERP component
  • much larger for infrequently occuring stimulus categories than for frequent ones (> in oddball)
  • P3b (most common): sensitive to task defined probability -> larger from improbable stimuli only, when the task requires sorting the stimuli in a way, that makes a given stimulus category improbable -> central and parietal brain regions
  • P3a (novelty): elicited by an improbable stimulus, even when the task does not require the discrimination of the stimulus -> frontal brain regions)
20
Q

What are motor ERP components?

A
  • if one creates averaged ERP waveforms, time-locked to a motor response, rather than time-locked to a stimulus, it is possible to see ERP components reflecting the processes that lead up to the response
  • readiness potential
21
Q

What is N170?

A
  • negative wave of visual cortex -> peaks at 170ms post-stimulus onset
  • larger when elicited by a facial stimulus
  • differentiation is first visible in 150ms post stimulus onset
  • brain can differentiate between faces and objects within 150 ms
  • abnormal in children with ASD
22
Q

What is P3/ P300?

A
  • seen when an attended stimulus is presented, expecially if the stimulus is relatively rare
23
Q

What is a readiness potential?

A

a large negative voltage, building over the motor cortex prior to a response

24
Q

What is a lateralised readiness potential?

A

a portion of the RP is larger over the hemisphere contralateral to the response than over the ipsilateral hemisphere

-> can be used to differentiate between RP and components reflecting stimulus processing (background activity)

25
Q

what is a capacitor?

A
  • two pools of charges separated by an insulating layer preventing ions from mixing
  • if ions would mix: emergence of a neutrally charged pool
  • example: electrode gel (removes air)
  • the sequence of layers in the brain function like a stack of capacitors = forming a series of conductive volumes, separated by insulating layers
26
Q

what is the inverse dipole modelling?

A
  • model of a spherical head is created by a computer and a dipole is placed somehwer ein this model
  • forward selection is calculated to determine the distribuion of voltages that this dipole would create on the surface
  • the predicted pattern is compared to the actual data
  • this is repeated until a good match is found
  • often more than 1 dipole is used
    –> ERPs are the result of processing in multiple brain areas (! inverse problem)
27
Q

What is the inverse problem?

A

Given a particular pattern of electricla charge on the surface of the sphere, it is impossible to determine the distribution of charge within the sphere that is caused

28
Q

what are solutions to the inverse problem?

A
  • modelling techniques are used: physics of the brain need to be simplified
  • important assumption: neural generates can be odelled as electrical dipoles
29
Q

What are exogenous sensory ERP components?

A
  • different ERP components for audiory vs. visual stimuli
  • ERO responses following visdual stimuli begin later than those for auditory ones
  • Odball paradigm (= most common ERP paradigm)
30
Q

What is the oddball paradigm?

A
  • part of exogenous sensory ERP components
  • standard stimulus (frequently) and oddball stimulus (infrequently) are presented briefly
  • participants count/ make a manual response to the oddball stimulus
  • the initial response to both stimuli: C1 wave (primary visual cortex) -> influenced by sensor factors but not task
  • P1 wave (extrastriate areas of visual cortex) -> influenced by sensory factors, attention, arousal
  • N1 wave (different brain areas) including sub-components involved in discriminating the identity of the stimulus influenced by attention
31
Q

What are the neural origins of ERP?

A
  • originate as postsynaptic potentials (during neurotransmission, when the binding of neurotransmitters to receptors changes the flow of ions across the cell membrane)
  • ERPS provide a direct and instantaneous, millisecond resolution measure of neurotransmission-mediated neural activity
  • main neurons measured as ERPs are the pyramidal cells, being the main input-output cells of the cortex
32
Q

What influences the polarity of ERP components?

A
  • orientation of the neurons (concerning the recording electrodes)
  • the location of the reference electrode
  • the part of the cell in which the neurotransmission is occurring
  • whether neurotransmission is excitatory or inhibitory?

methods of cognitive neuroscience (9 decks)

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