EEG

Question 1

What does EEG measure?

Answer 1

The difference in potential between 2 electrodes
(At least 2 are needed to get a signal)

Question 2

What does EEG reflect in the brain?

Answer 2

The summation of synchronous activity of millions (thousands or millions)

Question 3

Where should the reference electrode be placed?

Answer 3

On a presumed inactive zone
(This cancels out only the noise)

Question 4

What is the ground electrode and where is it usually placed?

Answer 4

Electrode that prevents interference if the power line noise

Often placed on forehead

Question 5

In the 10-20 system what is the distance between each electrode?

Answer 5

10-20% of the length of the skull (front to back or left to right)

Question 6

Why does the Maudsley system treat each hemisphere independently?

Answer 6

To account for asymmetries

Question 7

In polygraphy what other variables might be recorded and why?

Answer 7

Eye (EOG)
Muscle (EMG)
Heart (ECG)

To understand the origin of artefacts, detect subtle changes and help to classify episodes

Question 8

What factors in a patient affect the frequency composition of background activity?

Answer 8

Age
Disease
Level of consciousness

Question 9

How does dominant rhythm change as one gets older?

Answer 9

Rhythm becomes faster
(Delta/theta in childhood, alpha in adulthood and old age)

Question 10

What rhythm is seen in these awake with eyes closed?

Answer 10

Alpha rhythm

Question 11

What rhythm is seen in drowsiness?

Answer 11

Delta (<4hz) and theta (4-7.5 Hz)

Question 12

What would a 50Hz artefact indicate?

Answer 12

One or more electrodes is poorly applied

Question 13

What might a muscle artefact indicate?

Answer 13

Patient isn’t relaxed (anxious)

Question 14

What does hyperventilation usually cause on EEG?

Answer 14

EEG slowing
May trigger epileptic activity

Question 15

How does an absence seizure appear on EEG?

Answer 15

Generalised spoke and wave discharges at 3Hz