Fisch EEG Primer Chapter 4 Flashcards
Spatial analysis of the EEG
Multichannel recordings of EEGs are used to
determine the distribution of potential changes over the scalp
A derivation consists of…
combination of electrodes in inputs 1 and 2 of any one ampifier
A montage consists of…
any combination of derivations using multiple channels of recording. Acts as a spatial filter
Bipolar derivations consist of…
pair of electrodes next to one another
The bipolar montage is best suited for analyzing…
low to medium amplitude waveforms that are highly localized
Common electrode reference montage consists of…
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
The common electrode reference montage is best suited for analyzing…
widespread potentials and interhemispheric differences
NOTE: if all channels show the same output activity then the activity is likely coming from the reference electrode.
Average reference montage consists of…
series of derivations in which all 10-20 electrodes are added together and placed in input 2 of every amplifier
The average reference montage is best suited for analyzing…
activity that is intermediate in nature between bipolar and referential montages
weight average referencing consists of…
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
The weight average reference is best suited for analyzing…
activity intermediate between average reference montage and bipolar montage
Laplacian (source derivation) consists of…
similar in nature to the weight average reference however only uses electrodes nearest input 1 for reference
The Laplacian (source derivation) is best suited for analyzing…
activity intermediate to bipolar and weight average reference montages
Source localization attempts to solve the…
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
Localization in bipolar montages is made by looking for…
true phase reversal caused by identical potential at input 2 of one derivation and input 1 of the second derivation (same lead)
How is a instrumental phase reversal different than a true phase reversal
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
True/False: A waveform that points up on an EEG recording is the result of a negative potential
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)
True/False: Phase reversals are always an abnormal finding
False: Phase reversals are the byproduct of the montage configuration.
True phase reversals are overall uncommon, but can be seen in which childhood form of epilepsy?
Feature of epileptiform spikes in benign rolandic epilepsy (with centrotemporal spikes)
True phase reversals are distinguished by which features on bipolar and referential montages?
bipolar: double phase reversal
referential: single phase reversal
Describe the end of chain phenomena..
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)
Magnetoenecphalography (MEG)
measures intracellular neuronal magnetic currents and can more accurately localize sources within the brain (adjunct to EEG for localizing activity - use limited by expense)
The American Clinical Neurophysiology Society Guidelines require that every EEG be performed with how many basic montages?
3 ( longitudinal bipolar (LB), transverse bipolar (TB), and reference (R))
