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electrodiagnostic > EEG > Flashcards

EEG Flashcards

1
Q

Which neurons are the mains contributors to scalp-recorded EEG signals

A

Pyramidal cells
Arranged in the perpendicular orientation to the cortical surface

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2
Q

What is the phase convention of EEG waveforms?

A

downard: +
upward: -

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3
Q

2 types of montage

A

Bipolar or referential

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4
Q

How is localisation of a discharge made using a :
a) bipolar montage
b) referential montage

A

a) analysing orientation + amplitude
b) analysing amplitude

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5
Q

what is a bipolar montage ?

A

Each electrode’s voltage is linked and compared to an adjacent one to form a chain of electrodes. In each chain, an electrode’s voltage is compared to that of the electrode behind it, so each tracing line is a pair of electrodes in which the voltage of the second electrode is subtracted from the voltage of the first. Because of this, in bipolar if the first electrode in the tracing line is more positive/higher than the second, you get a positive, downward deflection; if the second electrode is more positive/higher, you get a negative, upward deflection.

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6
Q

How to interprete phase reversal in a bipolar montage?

A

With phase reversals, the middle electrode of the pair that makes the reversal is the electrode of maximal voltage.
Negative discharges cause the surrounding tracings to point toward the electrode of maximal voltage, while positive discharges cause surrounding tracings to point away from the electrode of max voltage (an easy way to remember this: positives can fit a plus sign, and negatives can only fit a negative sign)

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7
Q

In a bipolar montage, what is an end of chain phenomenon?

A

Occurs when potentials appear with greatest voltage in the last electrode in the chain of electrodes producing waveform deflections that are all in the same direction (no phase reversal). Solution: use another type of bipolar montage (e.g. circumferential montage).

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8
Q

What is a referential montage

A

Compare all the electrodes to single reference point.

There are no phase reversals, and as such, the highest amplitude waveform is the one with the greatest voltage, be it downward or upward.

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9
Q

What is a major limitation to the reference montage?

A

When the active electrode is the reference electrode, all the traces will be deflected in the same direction (following the reference signal). Creates a reference electrode artifact.

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10
Q

Define low f (high pass) filter

A

filter out frequencies below a certain threshold

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10
Q

Define notch filter

A

selectively removes 60 Hz activity that arises from electrical interference such as wires and equipment

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11
Q

Define sensitivity

A

Affects the height of the waveforms.
Higher Se = Lower number = smaller waveforms

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12
Q

Name the 4 frequency bandwiths

A

from low frequency/high amplitude –> high frequency/low amplitude
Delta (<4 Hz) - deep sleep
Theta (4-8 Hz) - sleep
Alpha (8-13 Hz) - Awake
Beta (13-30 Hz) - Stimulated / mental activity
Gamma, low (30-60 Hz)
Gamma, high (>70 Hz)
Ripples (> 100 Hz) - epileptiform discharges
Dans TA Bouche GRos

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13
Q

Name the patient-origin, physiological artifacts (7)

A

Scalp muscles (EMG)
Eye movements (EOG) - blink (up/down), REM (lateral)
Cardiac muscles (ECG)
Breathing
Blinking
Tongue and jaw mts (e.g. chewing)

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14
Q

Name the external, non physiological artifacts (4)

A

Intstrumental
Electrode
Environmental
Digital

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14
Q

Describe the Blink artifact. what is the underlying phenomenon?

A

Large positive (downward) deflection as the eye move upward in its orbit. Only seen in the frontal leads (F3 or F7).
Is a key component of normal, awake EEG.

It is caused by the Bell’s Phenomenon. The eyes’ cornea is positively charged and retina is negatively charged; when you blink, the eyes roll up slightly, and the cornea moves closer to the frontal electrodes Fp1 and Fp2, which thus see a positive signal that is reflected on EEG.

http://www.eegpedia.org/index.php?title=Eye_blink_artifact

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15
Q

Describre muscle artifacts

A

High frequency (40-70Hz), low amplitude. Often dominant in the frontal and lateral tempora leads.

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15
Q

Describe lateral eye movements (e.g. REM sleep)

A

Positive frontal deflection on the side to which you look, and a contralateral negative frontal deflection (opposite waveforms in bilateral frontal regions)

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15
Q

Describe an electrode pop

A

Single electrode showing a very sudden, steep upslope with a slower downslope and absolutely no field.

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15
Q

Describre chewing artifacts

A

Diffuse bursts of fast myogenic artifact; hypoglossal artifact is diffuse and slow, synchronized activity

16
Q

Describe ECG artifacts

A

Look like negative spikes time-locked to the QRS complex

17
Q

Decribe a chewing artifact

A

Muscle artifact from the temporalis muscle. Marked by sudden onset, intermittent bursts of generalized very fast activity.

18
Q

Describe a hypoglossal artifact

A

It arises from the movement of the tongue, and appears as slower, diffuse delta frequency activity.

19
Q

Know how to recognize different states of arousal

A

Awake: BETA (13-25 Hz). High f, low A. Blink + muscle artifacts.
Relaxed: ALPHA (8-12 Hz). Eyes closed.
Stage 1: THETA (4-7 Hz). Vertex waves.
Stage 2: K-complexes + sleep spindles
Stage 3-4: DELTA (1-3 Hz). Low f, high A.
REM: Similar to awake but no muscle artifact (atonia). Eye artifacts may be present.
https://www.macmillanhighered.com/BrainHoney/Resource/22292/digital_firs

20
Q

What is a sleep spindle

A

Burst of bursts of 11–15 Hz activity, typically between 0.5 and 2 s in duration. Often associated with K-complexes.

Feature of stage 2 nREM sleep

21
Q

What is a k-complex

A

Max at the vertex (Cz) or Fz
Diphasic
Duringe nREM stage 2
Often associated with sleep spindles

https://eegatlas-online.com/index.php/en/alphabetical-index/k-complex-gu

22
Q

what is a vertex sharp wave

A

Max at the vertex (Cz)
Diphasic
Found in nREM stage 1 +/- 2
smaller amplitude and narrower than K compexes
http://www.eegpedia.org/index.php?title=Vertex_waves

23
Q

Asymmetric (focal) decreased amplitude may indicate..

A

Focal structural cortical lesion (infarct, hematoma, tumor)

24
Q

Generalized decreased amplitude may indicate

A

widespread cortical dysfunction (post-ictal, hypothermia, subdural hematoma, post-anoxic..)

25
Q

Criteria for epileptiform discharges

A

High amplitude
Polyphasic
Different from background
Predominantly negative polarity
Multiple electrodes involved

26
Q

Spike

A

Negative, 20-70 ms

27
Q

Sharp wave

A

Negative, 70-200 ms (wider than spikes)

28
Q

Ictal vs interictal

A

Ictal: > 3s and/or associated with clinical manifestations (e.g. myoclonus)
Inter-ictal: < 3s except if associated with clinical manifestations

28
Q

Spike and slow-wave (SWC)

A

Negative spike followed by 200 ms negative wave

28
Q

Name and recognized 4 ictal activity waveforms

A

Spike-wave (3-5 Hz)
Polyspike-wave
Polyspike (16 Hz)
Polysharp (12 Hz, wider)

29
Q

Burst suppression

A

Found in GA or coma
if suppression is getting longer = neg Px factor for recovery from coma

30
Q

The biological signal with the largest signal frequency range, and thus requiring the highest low pass filter setting, is the:​
1. Electroretinogram (ERG)​
2. Electromyogram (EMG)​
3. Evoked potential (EP)​
4. Electrocardiogram (ECG)​
5. Electroencephalogram (EEG)

A

Evoked potential (EP)​

31
Q

Why is it desirable to minimize the impedances of body tissues, electrode-tissue interface, and electrodes when recording a bioelectric signal?​

  1. To reduce the potential for electric shock​
  2. To minimize capacitance at the electrode-tissue interface​
  3. To reduce subject discomfort​
  4. To present the greatest portion of the signal to the amplifier input
A

4

32
Q

Which one of the following is not a means to reduce 60 Hz artifact in a recording?​

  1. Differential recording​
  2. Using a ground electrode​
  3. Balanced and low electrode impedances​
  4. Not placing the animal on a metal surface​
  5. Notch filtering
A

Not placing the animal on a metal surface

33
Q

What is the definition of EEG background activity?​

A

Any EEG activity representing the setting in which a normal or abnormal pattern appears and from which such pattern can be distinguished.​

34
Q

Which of the following are considered epileptiform discharges?​

  1. Spindles​
  2. Periodic complexes​
  3. Burst suppression​
  4. All of the above
A

Periodic complexes​

35
Q

What is the age of maturity for background EEG rythms in dogs?​

A

It takes from 5 to 12 months for background EEG rhythms to reach maturity in the dog and cat​

2 year in another paper: “The characteristics of the EEG corresponding to the adult animal begin to appear at 12 months of age but stabilize after 24 months of age.”​

36
Q

By convention, an upward deflection in an EEG tracing indicates:​
1. That IT1 is negative with respect to IT2​
2. That IT1 is positive with respect to IT2​
3. That IT2 is positive with respect to IT1​
4. Both 1 and 3
5. Both 2 and 3

A

Both 1 and 3

37
Q

The EEG waveform spectrum in order from lowest to highest frequency is:​
1. Alpha, beta, gamma, delta, theta​
2. Delta, theta, alpha, beta, gamma​
3. Beta, theta, alpha, gamma, delta​
4. Gamma, beta, alpha, theta, delta

A
  1. Delta, theta, alpha, beta, gamma​
38
Q

Event localization in a bipolar EEG montage is based on ____ and in a ____ it is ____.​

  1. Phase reversal, unipolar, maximal amplitude​
  2. Maximal amplitude, referential, phase reversal​
  3. Phase reversal, referential, maximal amplitude​
  4. Phase reversal, unipolar, minimal amplitude
A

3.

39
Q

EEG artifacts are due to:​
1. Eye movements​
2. Ear movements​
3. Muscle tension​
4. Electrical interference​
5. All of the above

A

5.

40
Q

As the recording location for a biological signal increases from the signal’s origin (distance r), the amplitude of the recorded signal:​
1. Does not vary based on distance​
2. Decreases by 1/r​
3. Decreases by 1/r^3​
4. Decreases by 1/r²​
5. Decreases based on the angle θ between the signal dipole and the recording point

A

4

41
Q

A high pass filter setting of 5 Hz would result in:
1. Loss or reduction of low frequency signal components, such as slow delta waves in the EEG​
2. Loss or reduction of 60 Hz artifact​
3. Reduced amplifier input impedance​
4. Loss or reduction of high frequency signal components, such as an EEG spike​
5. A higher amplitude recorded signal

A
  1. Loss or reduction of low frequency signal components, such as slow delta waves in the EEG​
42
Q

Visual evoked potentials are:​
1. Present in prey animals at birth​
2. Absent in neonatal prey animals​
3. Indicate lens disease​
4. Indicate blindness due to trauma

A

1.

electrodiagnostic (8 decks)

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