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Biopsych PSYC20006 Theme 1 > EEG > Flashcards

EEG Flashcards

1
Q

What is EEG in one sentence? What do they pick up?

A
  • Detect neural activity using electrodes on scalp
    • Pick up small fluctuations of electrical signals from activity of (mostly cortical) neurons
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2
Q

Is EEG extra or intra-cranial?

A
  • Extra-cranial/Scalp
    • Non-Invasive
  • Intra-Cranial
    • Measure directly at exposed cortex
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3
Q

Who invented EEG?

When and how?

A
  • Hans Berger.
  • Detected first EEG with wife’s scalp in 1924.
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4
Q

What is the Alpha Rhythm?

A
  • Inconsistent electrical signal varying between 8 - 13 Hz.
  • Resting signal when someone closed their eyes.
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5
Q

What are the pros of EEG?

A
  • Cheap
  • Good Temporal Resolution
    • ms accuracy
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6
Q

What are the cons of EEG?

A
  1. EEG signal biased to Gyri
    • Sulci harder to detec
    • Masked by gyri signals
  2. Meninges, CSF and skull “smear” EEG signal, makes localisation difficult
    • Inverse Problem
  3. Poor Spatial Resolution
    • 1-10cm (10-100mm)
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7
Q

What is the inverse problem?

A
  • If the diple solutions are known, the resulting scalp configuration of signals can be reconstructed
  • However, one given scalp configuration of signal = Multiple dipole solutions
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8
Q

What is EEG signal measured in relation to?

A

In relation to a reference electrode, which is either:

  • a neutral point like nose
  • average of all scalp electrodes
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9
Q

How is EEG Recorded: What are the 4 tools?

A
  • (1) Electrode Cap > (2) Amplifier > (4) EEG Recording
  • (3) Experimental Stimulation > (4) EEG Recording
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10
Q

What are the channels in EEG?

A

10 – 32 – 64 – 128 – 256 channels

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11
Q

How are numbers on the scalp displayed in EEG?

A

Split cortex odd and even

F = frontal P = parietal C = central O = occipital T = temporal

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12
Q

What is the neurophysiology of the EEG Signal?

What is it NOT?

A
  • EEG activity orginates from post-synaptic potential
    • Voltage when NT binds to post-synaptic membrane’s receptor
    • Causes ion channels to open/close, leading to graded changes in potential across membrane

Note: EEG does not record action potential

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13
Q

What can the post-synaptic potential be considered as?

Can we record one post-synaptic potential?

A
  • A small dipole
  • Signals from single cells are not strong enough to be recorded outside of the head
  • If many neurons spatially align, then their summed potentials add up and create the signals we can record
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14
Q

Many neurons spatially align > summed potentials add up and create the signals we can record: What is this called and Where is the origin?

A

Pooled activity

  • From large number of similarly oriented neurons from large cortical pyramid cells
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15
Q

What is the functional unit of EEG? i.e. How many Neurons must be spatially aligned to record?

A

The functional unit is >10,000 simultaneously activated neurons

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16
Q

What determines the sign of the recorded potentials?

Can all of them be recorded?

A
  • Orientation of the neurons determines the sign of the recorded potentials.
  • Some orientations lead to signals which cannot be recorded.
17
Q

What is the typical amplitude of EEG and what are the steps to make a clear EEG output?

A
  1. 10μV to 100μV (Tiny)
  2. Amplified by factor of 1,000 to 100,000x
  3. Signal is typically digitalized. Typical sample frequency is 256-1024Hz, but can be >4000Hz
  4. Signal is band-pass filtered to remove the low (<0.5-1Hz) and high frequencies (typically >35-70Hz) because they cannot reflect brain activity.
18
Q

What is the most relevant step in EEG signal analysis? What are some examples?

A

Artefacts Removal, removing stuff that are not brain signals

  • Sweating
  • Electrical noise (“notch filter”)
  • Eye movements and blinks
19
Q

How does eye movement affect EEG?

How do we prevent it?

A
  • Eye = Dipole
    • Signals from eye contimates EEG signal to large degree
  • Record eye signal by placing electrodes next to and under the eye to capture horizontal and vertical eye movements
  • Remove by excluding contaminated trials, or mathematical algorithms, such as ICA
20
Q

Despite EEG signals being very noisy, the dominant frequency in the signal can be determined due to…

A

The raw signal shows systematic variations, and more of a specific frequency

(Delta, Theta, Alpha, Beta, Gamma) inconsistent characteristic frequency

21
Q

What was wrong with single EEG-trial studies?

What should we do then?

A

Noisy: Too much variance (Fluctuations)

  1. Between sessions from same participants
  2. Between participants
  • Averaging over lots of trials will reduce noise.
22
Q

How does an ERP look like? What is P and N?

A
  • Up and down fluctuations
    • Positivity is downwards.
    • Negativity is upwards.
23
Q

What are ways of reading ERP?

A
  • Peak-amplitude
    • 70% of studies
  • Area-under-the-curve
    • 20% of studies
  • Peak-to-peak
    • 10% of studies
  • Onset of component
    • Ambiguous

No clear rule. Results will differ across methods

24
Q

Woodman and Luck (1999): What is the signal they used and what did it index?

A
  • N2pc as an index of attention.
  • Attending left = Stronger N2pc right hemsphiere
    • N2pc = 2nd Negative Posterior Contralateral
25
Q

Woodman and Luck (1999): What are the Study Aims, Overview and Hypothesis?

A
  • Aims
    • Parallel / Serial
  • Visual Search Task
    • Search a coloured square
  • Hypothesis
    • Serial: Attention switch (N2pc) from one hemifield to the other, until the target is found .
    • Parallel: No N2pc Switch
26
Q

Woodman and Luck (1999): What are the Study Methods? How did they get the participant to attend to one hemifield first?

A
  • Manipulated probability specific colour was target (C75 and C25) to get people to attend to one hemifield
    • Particiapnts attend to C75 and can monitor attention while particiapants visually scanned
27
Q

Woodman and Luck (1999): What are the Study Results and Conclusion?

A

Target Absent

  • When C75 and C25 (same field), no shift in N2pc
  • When C75 and C25 (contralteral), shift in N2pc

Target Present

  • When C75 target and C25 (contralateral), no shift inN2pc
  • When C75 and C25 target (contralteral), shift in N2pc

Conclusion: People search in serial

(note looking at crossover of N2pc)

28
Q

Gehring et al., 1993: What are the Study Aims?

A

Whether there is mechanism for the detection and compensation for errors.

29
Q

Gehring et al., 1993: What is the signal of interest?

A

ERN

  • Negative deflection of up to 10μV in amplitude observed at central electrodes ~80-100ms after an erroneous response
30
Q

Gehring et al. (1993): Describe the Study Methods. What was manipulated? And what is the hypothesis?

A
  • Method Flanker-task (Middle Letter)
    • 3 Conditions
      • Emphaise Accuracy
      • Emphaise Speed
      • Control
  • H1.) Incongruent displays should lead to more errors
  • H2.) Error detection should only matter in the accuracy condition
31
Q

Gehring et al. (1993): Was the First Hypothesis supported?

A

Yes. ERN on incorrect trial in comparison to correct trials

32
Q

Gehring et al., 1993: Was the Second Hypothesis supported? What else were they interested in finding out?

A

Yes. The ERN was strongest when people emphasised accuracy, and weakest for speed

But is the ERN indicative for compensating for errors?

  • If this were true, one would expect that the ERN should also reflect the attempt to break the error
33
Q

Gehring et al., 1993: What is the method in the Further study of ERN compensation for errors (reflective of breaking the error)?

A

Investigated how ERNs of different sizes were related to response parameters (might be involved in error correction)

  • Divided into quartiles from small to XL
34
Q

Gehring et al., 1993: What is the results in the Further study of ERN compensation?

A

As ERN increases,

  • Lowe Response Force
    • Error correction
  • Higher Probability of right the next trial
    • Learning
  • Slower response on next trial
    • Post-error slowing
    • Learning

Biopsych PSYC20006 Theme 1 (6 decks)

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