Electroencephalogram (EEG)

Question 1

What is EEG and how is it used practically?

Answer 1

EEG is used to measure the functioning of the brain/electrical activity of the brain. It can be recorded during resting or active states, giving it a substantial value over other technologies. It measures the outcome of an action potential.
Neurotransmitters bind to post-synaptic receptors -> headed IPSPs and EPSPs

EEG can be used as a diagnostic marker of ADHD, medication effects, outcome measure for training students and as a basis for all ERP studies

Question 2

List and describe the five main EEG bands.

Answer 2

Delta

• Seen in state of deep sleep, very young children
• 0.5-3.5Hz, 20-200V
• Lowest frequency, large amplitude

Theta

• More frequent in children, indicator of maturational lag and general marker of dysfunction if the patient is alert and awake.
• Only a very small percentage in the EEG for a healthy adult
• 4-7Hz, 20-100V

Alpha

• Posterior dominant, indication of less neural activity in that part of the brain because that’s the primary visual processing pathway
• Relaxed waking state, eyes closed, mental inactivity
• Hypoarousal
• 8-12Hz, 20-60V

Beta

• Fast wave activity, waking state, mental activity
• Frontocentral
• 13-25Hz, 2-20V

Question 3

Compare monopolar EEG recording and bipolar EEG recording.

Answer 3

Monopolar EEG recording is most common and involves a reference electrode and an electrically inactive part of the body such as the tip of the nose or the earlobe. This is used as a 0 to compare the active electrode against

Bipolar EEG recording is less frequently used and uses two different active electrodes to compare two sites

Question 4

What is the international 10-20 system?

Answer 4

A convention which sets the standards as to where to put the electrodes and allows for a comparison of results. 10-20 refers to the distance between a couple of landmarks, like the ears or nose. Electrodes are placed based on measurements between several points, with most electrodes placed at intervals of either 10% or 20% of the distance
Odd numbers on the left, even on the right and the midline if referred to as ‘Z’
Alternatively, you can use an electrode cap, which had the electrodes built in at these distances

Question 5

What are two main ways to quantify EEG?

Answer 5

Time domain (record): amount of EEG activity within a period

Frequency domain (analyse): the quantification of the amount of power within a given EEG frequency

Question 6

Explain Fast Fourier Transformation (FFT).

Answer 6

FFT is an efficient algorithm that analyses each waveform and quantifies the amount of power contained within it

Question 7

What is the difference between absolute and relative power. How do we calculate relative power?

Answer 7

Absolute power – a measure of the magnitude of the power in the EEG or a specific frequency band, measured in microvolts squared

Relative power – the amount of power that one frequency band contributes to the entire power of the EEG, expressed at as %
E.g. Relative theta= (absolute theta)/(absolute (delta×theta×alpha×beta)×100)

Question 8

If the shape of the EEG is similar at two electrode sites, what does this indicate?

Answer 8

Then there is a strong connectivity. High coherence indicates that two locations share functional and/or structural connections.

Question 9

Describe the process of alpha blocking/EEG activation.

Answer 9

It is the change from alpha activity to beta activity with stimulation or demand. This transitional period is measurable and often caused by eyes opening, mental stimulation or sound.

Question 10

Does one hemisphere become differently activated during different tasks?

Answer 10

EEG hemisphere asymmetry occurs when the power on one side is greater then the other, or when change in frequency from resting state to an active state is greater only in one hemisphere.

Research has suggested hemispheric specialisation:

• Left hemisphere - language and mathematical tasks
• Right hemisphere - spatial ability

Studies with infants have found that happiness activated the left frontal region, therefore, it has been linked to positive emotions

Question 11

What happens to EEG when as an individual matures?

Answer 11

• Delta and theta decrease in relative power by about 4% per year
• Alpha and beta increase up until about 18 years

Question 12

How does the topography differ for each of the EEG bands?

Answer 12

• Delta, theta, alpha – development occurs first in the posterior regions, then central and frontal regions. New evidence suggesting development until 25-30 years
• Beta band – development occurs first centrally, then posterior regions, finally frontal regions

Question 13

Describe the relationship between EEG and intelligence.

Answer 13

EEG is argued to reflect biological intelligence or efficiency of brain functioning.

Question 14

List and describe the EEG characteristics at each sleep stage.

Answer 14

Waking - Low V, mixed Hz

Stage 1 - Low V, mixed Hz, much of it 2-7Hz (includes delta and theta)

Stage 2 - Low V, mixed Hz. 12-14Hz sleep spindles. K complexes (high V, positive and negative spikes, indication of OR)

Stage 3 - 20-50% large, slow delta activity

Stage 4 - More than 50% delta activity (cortex activity reduced, restoration)

REM - Low V (similar to waking state), mixed Hz. Episodic rapid eye movements (dreaming). EOG increases, respiration increases BP increases, BV in genitals increases and muscle tone decreases

Question 15

What is EEG artifact and what causes it?

Answer 15

EEG only records electrical activity under the electrode where it is placed. It does not know the difference between what is brainwave activity, and what is not.
Artifact is everything in the EEG that is not brain activity

Causes:
- Eye blinks
- Eye movement artifact
- General muscle activity – Electromyogram (EMG) – measures the electrical activity of muscles when they’re at resting and when they’re being used. Amplitude and frequency relation is not necessarily inverse in EMG. You can get large, high amplitude signals; therefore, it is easy to identify as muscle and remove it. Muscle contraction usually produces very high frequency (>50Hz) variable amplitude artifact
o Glossokinetic – due to tongue movement, low frequency, maximal over temporal leads
- Shoulder tension – high frequency/high amplitude signal
- Frown, head movement, swallow
- Sweat artifact – sweating produces very slow (0.5Hz) large potential shifts inconsistent with cerebral activity. May be similar to eye rolling artifact
- Phone ring artifact

Question 16

List the methods of removal for EEG artifacts.

Answer 16

• Filtering the data – can be filtered before or after it is recorded. Filters remove specific frequency band data that are not required for your research. Use of notches to isolate said band. Usually built into the EEG system-
• Combined filtering is usually applied
  Low pass – removes high frequency part of the spectrum. Usually anything above 30Hz is muscle artifact
  High pass – removes low frequency part of the spectrum, usually sweat. Primarily set to remove eye activity. Should not be set at zero
• Correction – uses an algorithm that adjusts the artifacted EEG back to what is believed to be normal. Able to understand the contamination and remove the contamination. Allows you to keep all your data. Problem is that most procedures appear to create as much distortion of the EEG as they correct
• Rejection – technician visually inspects the trace and removes parts that are not believed to be real brainwave activity. This method removes the ability to replicate the study, you can’t replicate something based on the technician’s decision. Increases potential for bias