Definitions for EEG – EEG Exam
Questions and Answers
Electroencephalogram - Answers -An instrument that generates a record of the
electrical activity of the brain by measuring electric potentials using electrodes attached
to the scalp.
Electroencephalograph - Answers -A chart of the brain waves picked up by the
electrodes placed on the scalp.
10-20 System - Answers -A system of electrode application on the scalp using
identifiable skull landmarks as reference.
Distributed using percentages of 10 and 20.
Montage - Answers -The particular arrangement by which a number of derivations are
displayed simultaneously in an EEG record.
Bipolar Montage - Answers -Chains of derivations that consist of electrodes along the
same array, where input 2 in one channels in input 1 in the next.
Transverse Montage - Answers -A montage consisting of derivations from pairs along
coronal (transverse) arrays.
Also called a Coronal Bipolar Montage.
Longitudinal Montage - Answers -A montage consisting of derivations from pairs of
electrodes along longitudinal, usually anterior to posterior, arrays.
Reference Montage - Answers -An arrangement of derivations in which one input 2 is
common to all channels.
Derivation - Answers -A pair of electrodes recorded in the EEG.
Polarity - Answers -The sign of potential different between an electrode affected by the
given potential and another electrode.
Artefact - Answers -Any potential difference due to an extracerebral source (either
physiological or mechanical) recorded in EEG tracings.
, Frequency - Answers -The rhythmic repetitive activity or the equivalent frequency of
isolated waves.
Rhythmic - Answers -A constant frequency.
Arrhythmic - Answers -A sequence of waves of inconstant frequency.
Voltage - Answers -The amplitude of a waveform. Refers to the average voltage or peak
voltage of EEG activity.
Attenuation - Answers -The reduction of amplitude of EEG activity resulting from
decreased voltage.
Hypersynchrony - Answers -An increase in voltage and regularity of rhythmic activity.
Paroxysmal - Answers -Activity that emerges from the background with a rapid onset.
Morphology - Answers -The shape of a waveform.
Monomorphic - Answers -One dominant waveform.
Polymorphic - Answers -Multiple frequencies that combine to form a complex waveform.
Sinusoidal - Answers -Waves resembling sine waves. Monomorphic activity is usually
sinusoidal.
Transient - Answers -An isolated wave or pattern that is distinctly different from the
background activity.
Spike - Answers -A transient waveform with a pointed peak and duration of 20-70
milliseconds.
Sharp wave - Answers -A transient waveform with a pointed peak and duration of 70-
200 milliseconds.
Complex - Answers -A sequence of 2 or more waves, not necessarily of the same
frequency, with a distinct form or pattern different from the background.
Biphasic - Answers -A wave or complex having 2 distinct components, one surface
positive and the other surface negative.
Triphasic - Answers -A wave or complex with 3 distinct components, such as (+-+) or (-
+-).
Quantity - Answers -The amount of a particular type of EEG activity with respect to
percentage time present and or voltage.
Questions and Answers
Electroencephalogram - Answers -An instrument that generates a record of the
electrical activity of the brain by measuring electric potentials using electrodes attached
to the scalp.
Electroencephalograph - Answers -A chart of the brain waves picked up by the
electrodes placed on the scalp.
10-20 System - Answers -A system of electrode application on the scalp using
identifiable skull landmarks as reference.
Distributed using percentages of 10 and 20.
Montage - Answers -The particular arrangement by which a number of derivations are
displayed simultaneously in an EEG record.
Bipolar Montage - Answers -Chains of derivations that consist of electrodes along the
same array, where input 2 in one channels in input 1 in the next.
Transverse Montage - Answers -A montage consisting of derivations from pairs along
coronal (transverse) arrays.
Also called a Coronal Bipolar Montage.
Longitudinal Montage - Answers -A montage consisting of derivations from pairs of
electrodes along longitudinal, usually anterior to posterior, arrays.
Reference Montage - Answers -An arrangement of derivations in which one input 2 is
common to all channels.
Derivation - Answers -A pair of electrodes recorded in the EEG.
Polarity - Answers -The sign of potential different between an electrode affected by the
given potential and another electrode.
Artefact - Answers -Any potential difference due to an extracerebral source (either
physiological or mechanical) recorded in EEG tracings.
, Frequency - Answers -The rhythmic repetitive activity or the equivalent frequency of
isolated waves.
Rhythmic - Answers -A constant frequency.
Arrhythmic - Answers -A sequence of waves of inconstant frequency.
Voltage - Answers -The amplitude of a waveform. Refers to the average voltage or peak
voltage of EEG activity.
Attenuation - Answers -The reduction of amplitude of EEG activity resulting from
decreased voltage.
Hypersynchrony - Answers -An increase in voltage and regularity of rhythmic activity.
Paroxysmal - Answers -Activity that emerges from the background with a rapid onset.
Morphology - Answers -The shape of a waveform.
Monomorphic - Answers -One dominant waveform.
Polymorphic - Answers -Multiple frequencies that combine to form a complex waveform.
Sinusoidal - Answers -Waves resembling sine waves. Monomorphic activity is usually
sinusoidal.
Transient - Answers -An isolated wave or pattern that is distinctly different from the
background activity.
Spike - Answers -A transient waveform with a pointed peak and duration of 20-70
milliseconds.
Sharp wave - Answers -A transient waveform with a pointed peak and duration of 70-
200 milliseconds.
Complex - Answers -A sequence of 2 or more waves, not necessarily of the same
frequency, with a distinct form or pattern different from the background.
Biphasic - Answers -A wave or complex having 2 distinct components, one surface
positive and the other surface negative.
Triphasic - Answers -A wave or complex with 3 distinct components, such as (+-+) or (-
+-).
Quantity - Answers -The amount of a particular type of EEG activity with respect to
percentage time present and or voltage.
