Fisch EEG Primer Chapter 4

Question 1

Multichannel recordings of EEGs are used to

Answer 1

determine the distribution of potential changes over the scalp

Question 2

A derivation consists of…

Answer 2

combination of electrodes in inputs 1 and 2 of any one ampifier

Question 3

A montage consists of…

Answer 3

any combination of derivations using multiple channels of recording. Acts as a spatial filter

Question 4

Bipolar derivations consist of…

Answer 4

pair of electrodes next to one another

Question 5

The bipolar montage is best suited for analyzing…

Answer 5

low to medium amplitude waveforms that are highly localized

Question 6

Common electrode reference montage consists of…

Answer 6

series of derivations in which the same electrode (reference electrode) is used in input 2 in each amplifier; produces higher amplitude EEG recording because of increased interelectrode distances

Question 7

The common electrode reference montage is best suited for analyzing…

Answer 7

widespread potentials and interhemispheric differences

NOTE: if all channels show the same output activity then the activity is likely coming from the reference electrode.

Question 8

Average reference montage consists of…

Answer 8

series of derivations in which all 10-20 electrodes are added together and placed in input 2 of every amplifier

Question 9

The average reference montage is best suited for analyzing…

Answer 9

activity that is intermediate in nature between bipolar and referential montages

Question 10

weight average referencing consists of…

Answer 10

similar to average refernce montage, except all electrodes do no contribute equally to input 2, input 1 is not included in the input 2 average - electrodes closest to input 1 are ‘weighted’ more heavily

Question 11

The weight average reference is best suited for analyzing…

Answer 11

activity intermediate between average reference montage and bipolar montage

Question 12

Laplacian (source derivation) consists of…

Answer 12

similar in nature to the weight average reference however only uses electrodes nearest input 1 for reference

Question 13

The Laplacian (source derivation) is best suited for analyzing…

Answer 13

activity intermediate to bipolar and weight average reference montages

Question 14

Source localization attempts to solve the…

Answer 14

inverse problem (essentially an impossible task with infinite number of possible solutions) - certain a priori assumption can applied which provide an estimate of likely intracranial source

Question 15

Localization in bipolar montages is made by looking for…

Answer 15

true phase reversal caused by identical potential at input 2 of one derivation and input 1 of the second derivation (same lead)

Question 16

How is a instrumental phase reversal different than a true phase reversal

Answer 16

An instrumental phase reversal is the product of montage configuration and does not represent an actual reversal in polarity seen in a true phase reversal

Question 17

True/False: A waveform that points up on an EEG recording is the result of a negative potential

Answer 17

False: an up going waveform is the result of the difference in potential between inputs 1 and 2 (i.e. more negative input 1 or more positive input 2)

Question 18

True/False: Phase reversals are always an abnormal finding

Answer 18

False: Phase reversals are the byproduct of the montage configuration.

Question 19

True phase reversals are overall uncommon, but can be seen in which childhood form of epilepsy?

Answer 19

Feature of epileptiform spikes in benign rolandic epilepsy (with centrotemporal spikes)

Question 20

True phase reversals are distinguished by which features on bipolar and referential montages?

Answer 20

bipolar: double phase reversal
referential: single phase reversal

Question 21

Describe the end of chain phenomena..

Answer 21

potentials that appear with the greatest voltage in the last electrode will produce waveform deflections in the chain of bipolar that are all in the same direction (i.e. no phase reversal)

Question 22

Magnetoenecphalography (MEG)

Answer 22

measures intracellular neuronal magnetic currents and can more accurately localize sources within the brain (adjunct to EEG for localizing activity - use limited by expense)

Question 23

The American Clinical Neurophysiology Society Guidelines require that every EEG be performed with how many basic montages?

Answer 23

3 ( longitudinal bipolar (LB), transverse bipolar (TB), and reference (R))