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Basic Principles in Neuroimaging > Lecture 5 EEG > Flashcards

Lecture 5 EEG Flashcards

1
Q

Which neurologist developed the first technique of recording electrical activity at the scalp?

A) Wegner
B) Berger
C)

A

B) Berger (1929)

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2
Q

What causes the electrical activity at the scalp measured by EEG?

A

When neurons fire they are changing electrical polarisation

When lots of neurons fire at the same time- the electrical activity sums and we are able to measure it

The activity of populations of neurons firing together produced a change in electrical polarisation in the brain

This can be measured by electrodes on the scalp in EEG

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3
Q

What makes signal diffusion a limitation of EEG?

A
  • The electrical signals have to pass through lots of tissue (including the skull) before you can measure them
  • This gives EEG very poor spatial resolution
  • Nearby electrodes are often highly correlated with each other
  • It is hard to tell where a signal is coming from
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4
Q

How are problems with sulci limitations of EEG?

A
  • Human brains are very convoluted (they have many folds)
  • Opposite potentials across a sulcus can cancel each other out
  • But the magnetic field should be OK because it is orthogonal
  • So MEG can sometimes detect signals that are lost to EEG
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5
Q

In EEG we are measuring a difference in electrical charge (the difference between two places)

What is the technical term for this difference?

A

Potential difference or voltage

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6
Q

Voltage is always measures as a relative.

There must always be a reference electrode.

Where can these electrodes be located?

A

Behind the ear, nose, leg, arm

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7
Q

EEG voltages are typically very large

True or False?

A

False

EEG voltages are very small.

  • The voltages we measure are tiny, typically in the order of tens of microvolts
  • A microvolt is a millionth of a volt
  • So much much less than a battery produces
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8
Q

Give examples of components of EEG

A

Electrodes
Electrode caps
Amplifiers
Triggers
Filters

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9
Q

What are electrodes traditionally made of?

A

Silver/ silver chloride

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10
Q

Are electrodes in EEG MRI or MEG compatible?

A

Usually no, but you can get specialised systems with electrodes that are compatible

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11
Q

What is a montage?

A

A standard referencing system to determine electrode placement

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12
Q

What is the most common montage?

A

The 10-20 system

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13
Q

In a 10-20 system, odd numbers are located on the right and even on the left, true or false?

A

True

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14
Q

In a 10-20 system, what do the following letters stand for?

O
P
T
F
C
A
M
z

A

O – Occipital
P – Parietal
T – Temporal
F – Frontal
C – Central
A – Anterior*
M – Mastoid
z – zero
* or sometimes earlobe

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15
Q

When placing a cap, what are the two reference points that determine where certain electrodes should sit?

A

The naison (just above the bridge of the nose)

The inion (the bump at the base of the skull)

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16
Q

What is electrical impedance?

A

Opposition to the electrical current

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17
Q

How can electrical impedance be lowered in EEG?

A

By using a conductive gel or paste

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18
Q

Is an impedance of <5 ohms considered good?

A

Yes

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19
Q

Why do EEG voltages need to be amplified?

A

Because they are too small

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20
Q

Online monitoring- contemporary systems give a live trace of all electrodes- what sorts of normal activities give off a response?

A

Blinking and clenching teeth

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21
Q

What are low pass filters?

A

Smoothing filters that make the waveforms easier to interpret

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22
Q

EEG has a high temporal resolution, true or false?

A

True

23
Q

Data analysis- why is it important to average waveforms over many trials?

A

Lots of noise- true signal can be revealed by averaging over multiple trials/ subjects

24
Q

Data analysis- what is artifact removal?

A

Removal of trials where data was corrupted by some artefact e.g. electrical equipment such as a fan

  • Different ways of getting rid of this data:
  • Various labs use different rejection criteria: e.g. removing trials where some measure exceeded ±3SE of the mean
  • Other sophisticated analysis techniques exist for detecting things like blinks, such as Independent Components Analysis (ICA)
25
Q

Blink detection

A
  • Blinks show up on the electro-oculogram at the bottom of the plot
  • But there are also voltage changes at some scalp electrodes
  • Some are positive, some are negative
  • ICA can use these to detect and remove blinks
26
Q

What is an event-related potential?

A

A complex waveform, averaged over many trials/ stimulus presentations
It has multiple positive and negative components
Everything is relative to stimulus onset in EEG

27
Q

In ERPs are negative voltages usually plotted upwards or downwards?

A

Upwards! Always check!

28
Q

Common ERPS

ERP components can also be labelled by the (approximate) time they occur in milliseconds

What is P100?

A

P100- Basic visual response (occipital)

29
Q

Common ERPS

ERP components can also be labelled by the (approximate) time they occur in milliseconds

What is N100?

A

N100- Basic auditory response

30
Q

Common ERPS

ERP components can also be labelled by the (approximate) time they occur in milliseconds

What is N170?

A

N170- produced by face stimuli

31
Q

Common ERPS

ERP components can also be labelled by the (approximate) time they occur in milliseconds

What is P300?

A

P300 reflects decision making

32
Q

Common ERPS

ERP components can also be labelled by the (approximate) time they occur in milliseconds

What is LRP (lateralised readiness potential)?

A

LRP- indicator of motor planning

33
Q

How are ERPs usually quantified (which two things are measured)?

A

Peak amplitude

Latency

34
Q

Multivariate pattern analysis is a newer technique for analysing EEG data, what do they show and how are they advantageous over traditional ERP averages?

A

MPA adds a temporal dimension to the analysis
MPA tells you more about information available
(??)

35
Q

What is Fourier Analysis?

A

A data analysis technique- any waveform can be broken down or constructed from the sum of sine waves of different frequencies
Fourier analysis- building up one waveform from lots of sine waves

36
Q

The EEG waveform and the Fourier spectrum represent the same information in different ways, true or false?

A

True

37
Q

Frequency vs time plots represent how the fourier spectrum changes over time, what does the colour represent?

A

The colour represents the amplitude (or the power, which is amplitude squared) at each frequency

38
Q

The brain produces synchronised activity in different frequency bands , what are some examples of these standard bands?

A

– Delta – <4Hz, sleep, some attention tasks
– Theta – 4-7Hz, similar to Alpha
– Alpha – 7-14Hz, resting, tiredness, attentional lapses
– Beta – 15-30Hz, motor behaviour, concentration
– Gamma – >30Hz, long range neural synchronization

39
Q

Steady state

A
  • An alternative technique is to make the brain oscillate at a particular frequency
  • We do this by making the stimulus oscillate in intensity at that frequency
  • Measure the ‘steady-state evoked potential’ – the amplitude at the stimulus frequency
  • Works for vision, hearing, somatosensory etc.
  • Advantage- you know exact frequency, intensity of stimulus can be changed
40
Q

What is source localisation (visualising responses)

A

The inferred location of activity in the brain from the distribution of activity across electrodes

41
Q

What are some uses and benefits of EEG for cognitive neuroscience (types of experiments)?

A
  • Almost all areas of cognitive neuroscience are investigated using ERP designs, e.g.
  • Face processing
  • Semantic processing
  • Memory
  • Learning
  • Motor tasks
  • Attention
  • The literature is huge
42
Q

What are some uses and benefits of EEG in clinical research?

A
  • Originally used to diagnose and monitor epilepsy, EEG monitoring is also used in a range of clinical conditions, including:
  • Migraine
  • Movement disorders (e.g. Parkinson’s)
  • Psychiatric disorders
  • Diagnosing brain death, coma etc.
  • It is now a standard clinical tool in some settings
43
Q

What are some uses and benefits of EEG in sleep research?

A
  • The different stages of sleep are associated with characteristic patterns of EEG activity
  • EEG can be used to investigate sleep disorders, and study consolidation of learning during sleep
44
Q

What are some uses and benefits of EEG in basic sensory research? (Steady state EEG is becoming more popular, what is a major advantage of this technique?)

A
  • Used widely in hearing, e.g. to assess hearing deficits, the efficacy of cochlear implants
  • For vision research, steady-state EEG is becoming more popular
  • Has the advantage that it can be used on subjects who cannot respond to a behavioural task, e.g. very young children. Developmental studies often use EEG
45
Q

EEG has excellent temporal resolution but poor spatial resolution, true or false?

A

True

46
Q

EEG has excellent spatial resolution but poor temporal resolution, true or false?

A

False

47
Q

fMRI has excellent spatial resolution but poor temporal resolution, true or false?

A

True

48
Q

Why use EEG? List EEG’s major advantages

A
  • It is cheap – consumables cost <£2 per subject
  • Doesn’t require major investment to set up a lab, and is widely available
  • It has excellent temporal resolution
  • Non-invasive, and easily combined with other techniques
  • Analysis techniques are well developed
  • But critically, use it because it helps you answer a question – the best research is driven by theory, not by methodology
49
Q

Give examples of some potential future uses of EEG

A

Human-computer interaction

  • We used to interact with computers using keyboards, then mice, now touch, what next?
  • Most manufacturers are investigating brain-computer interfaces

Gaming headsets

Neurofeedback

  • Some people have tried to use EEG as a way of monitoring their own internal mental state
  • A bit like biofeedback for adjusting your own heart rate, aiding meditation, relaxation, stress or anger management etc.
  • This may or may not work, but it is an interesting use of the technology, and has produced a range of very cheap, but potentially useable consumer hardware
50
Q

An EEG waveform measures the change over time of the

Current at a point on the scalp

Voltage at a point on the scalp

Voltage between two points on the scalp

Current between two points on the scalp

A

Voltage between two points on the scalp

51
Q

Special equipment is required to combine EEG with MRI or MEG because

Standard EEG electrodes give off powerful magnetic fields

The liquid helium used to cool the MEG sensors reacts with EEG gel

Standard EEG systems contain too much metal

There is insufficient space inside the MEG/EEG scanner for normal electrodes

A

Standard EEG systems contain too much metal

52
Q

A contour plot shows

the distribution of activity across sensors at a specific point in time

a fourier analysis of all sensors along a single axis

the ratio of induced to evoked activity

the source location of EEG/MEG signals at different time points

A

the distribution of activity across sensors at a specific point in time

53
Q

In regard to the N and P waves of the EEG, N and P stand for

neocortical and paleocortical

novel and practiced

negative and positive

nascent and persistent

A

negative and positive

Basic Principles in Neuroimaging (9 decks)

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