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EEG Terminology

EEG

TermDefinition
Pseudo-Rhythmic Recurrent Sharp Waves The term previously used to describe periodic lateralized epileptiform discharges also known as PLEDs. (Chatrian 1961)
PLEDs Periodic epileptiform discharges that occur in a focal or lateralized manner over one hemisphere.
PRFD Periodically recurring focal discharges. (Hughes and Schlagenhauff 1965)
Cerebral Bigeminy Alternating ipsilateral periodic lateralized epileptiform discharges. Two separate foci of periodic activity with alternating amplitudes ad morphology are present over the same area or hemisphere.
PLPD Pseudoperiodic lateralized paroxysmal discharges. PLEDs in which the repetition rate is not precisely regular.
BIPLEDs Bilateral PLEDs that occur independently between cerebral hemispheres.
PSPA Periodic sinusoid paroxysmal activity. Bursts of sinusoid activity around 7-9 Hz, usually followed by a slow wave, lasting less than 500 ms, with a period less than 2 s. Mainly over the posterior head regions, associated with confusional state.
Chronic PLEDs Persistent PLEDs over long periods of time.
PEDIM Periodic epileptiform discharges arising from the centro-parietal midline sagittal region.
Poly PLEDs Periodic lateralized epileptiform discharges followed by after-discharges occurring in clusters.
PLEDs Plus PLEDs with rhythmical discharges that are more likely to be associated with clinical seizures.
PLEDs Proper PLEDs with no associated rhythmical discharges.
Sequential PLEDs PLEDs that occur sequentially between consecutive seizures.
Tri-Focal PLEDs PLEDs that occur in three independent sites.
Tri-PLEDs Tri-focal independent periodic lateralized epileptiform discharges occurring in three different areas.
IpsiIPs/Ipsi PLEDs Periodic discharges arising from ipsilateral independent foci.
Multi-Focal PLEDs PLEDs that occur in at least three independent site and involve both hemispheres,
EEG (Electroencephalography) The process of amplification, recording, and analysis of the electrical potentials of the brain,
Electrocorticography The result of electrical activity directly from the surface of the cerebral cortex either during surgery or post surgery using implanted electrodes.
Lead A single electrodes placement on the scalp or other recording area. Also used to describe the electrode itself.
Electroencephalograph The instrument used to amplify and record the electrical potentials of the brain.
Electroencephalogram The EEG recording itself.
ND (Neurodiagnostics) An umbrella term that refers to all types of neurophysiologic testing and monitoring.
Sagittal Relating to or situated on the imaginary plane that divides a human or animal body into right and left halves.
Derivation One set of 2 electrodes, placed into Grid 1 and Grid 2 of one channel of the electroencephalograph.
Horizontal Dipole When the surface electrodes are able to record both the negative and positive ends of a generator.
Bipolar Refers to the montage which consists of chains of electrodes going from anterior to posterior, left over right, in temporal chains and parasagittal chains across the head.
Monatge An organized combination of electrode derivations recording at the same time on the electroencephalograph.
Dipole Having two equal and opposite magnetized or electrically charged poles that are separated by a short distance.
Monopolar Refers to a montage that is referential.
Vertex The very top. In EEG it is Cz.
Dura Mater The outer most toughest layer of the meninges.
Arachnoid Mater The web like middle layer of the meninges.
Pia Mater The innermost layer of the meninges.
Transverse In EEG, it is a montage that goes crosswise across the head from left to right.
Discharge Used to describe paroxysmal patterns such as epileptiform patterns and seizure patterns.
Meninges The three membranes enveloping the brain and spinal cord. The three layers are called Dura, Arachnoid, and Pia.
Parasagittal In EEG, the 2 planes running front to back on either side of the midline.
Channel In EEG, one line of activity derived from 2 electrodes input into a differential amplifier.
Gyrus One of the elevations in the convolutions of the surface of the brain caused by the in-folding of the cortex.
Gyri Plural of gyrus.
Cortex The convoluted layer of grey matter covering the surface of the cerebral hemispheres about half of which is hidden within the folded walls of the sulci.
Central Sulcus aka Rolandic Fissure The central sulcus is a prominent landmark of the brain, separating the parietal lobe from the frontal lobe and the primary motor cortex from the primary auditory somatosensory cortex.
Extra Cerebral Term indicating a location not on the head.
Meningitis Inflammation of the meninges.
Sulcus Literally a groove, trench, or furrow. A general term used to designate such a depression especially those on the surface of the brain.
Sulci Plural of sulcus, as in the "sulci of the brain."
Homunculus A pictorial representation of the anatomical divisions of the primary motor cortex and the primary somatosensory cortex.
Medial Toward the midline of the body.
Lateral Away from the midline of the body.
Proximal Toward a reference point (extremity).
Distal Away from a reference point (extremity).
Inferior Lower or below.
Superior Upper or above.
Cephalad or Cranial Head.
Caudal or Cauded Tail, tail end.
Anterior Toward the front.
Posterior Toward the back.
Dorsal Posterior.
Ventral Anterior.
Dermatomes An area of skin that is mainly supplied by a single spinal nerve.
Hertz Unit of frequency. Cycles per second.
Gamma The frequency band in EEG containing faster frequencies above 30 Hz.
Beta The frequency band in EEG containing faster frequencies 13 Hz to 30 Hz.
Alpha The frequency band in EEG containing frequencies from 8-13 Hz.
Theta The frequency band in EEG containing frequencies from 4 Hz to less than 8 Hz.
Delta The frequency band in EEG containing frequencies less than 4 Hz.
Cycles per Second Unit of frequency. Also called Hertz abbreviated Hz.
Cycles A complete series of changes undergone by a wave or complex before the series of changes are repeated.
Dipole Having two equal and opposite magnetized or electronically charged poles that are separated by a short distance.
Frequency Defined as cycles per second.
Monopolar Literally means having one pole. In EEG it refers to a montage that is referential. The term is misleading because both electrodes in a referential montage contribute electrical potentials to the differential amplifier and are actually active.
Bilateral Both sides, in EEG is means occurring over both hemispheres.
Lateralized Occurring only over one hemisphere.
Horizontal Dipole When surface electrodes are able to record both the negative and positive ends of a generator.
Bipolar Having two poles. Refers to montages that are "scalp to scalp".
Background Activity Activity representing normal patterns or the activity present in abnormal patients during resting asymptomatic periods.
Dominant Frequency The frequency of activity the occupies the greater part of the recording.
Diffuse Widespread, occurring over large areas of one or both hemispheres.
Bancaud Phenomenon Uncommon unilateral failure of the alpha to attenuate with eye opening. It may occur in lesions of the temporal or parietal lobes.
Unilateral Restricted or remaining in one hemisphere.
Sub-harmonic Frequency that is below the fundamental frequency, a frequency that divides evenly into the fundamental frequency.
Harmonic A wave or frequency that is an integral multiple of a given fundamental frequency. Seen in photic driving responses and sometimes in electrical noise.
Alpha Squeak A transient increase in alpha frequency immediately following eye closure.
Photovoltaic Technically means generating electrical power by converting light energy. In EEG it refers to an artifact caused by the photic stimulator in the frontal leads. The artifact is eliminated by covering the electrode with something to shield the light.
Topography Refers to the distribution of a pattern or waveform over the surface of the brain.
Focal In a clearly delineated area of the brain in a focal temporal spike or focal slowing.
Ipsilateral On the same side. In an Ipsilateral Ear Reference Montage, it refers ti all the electrodes in Grid 1 to the ear of mastoid on the same side of the head.
Contralateral Relating to the opposite side of the head or body.
Generalized Occurring simultaneously throughout the recording electrodes. A discharge can be primarily generalized or secondarily generalized.
Multifocal Having two or more spatially separated sites of origin.
Temporal Situated in or arising from the temporal lobe.
Central Situated in or arising from the area of the brain around the central sulcus.
Frontal Situated in or arising from the front.
Occipital Posterior portion of the brain just above the cerebellum responsible for the processing of vision.
Parietal Situated in or arising from the parietal lobe.
Focus A limited region of the scalp, cerebral cortex or depth electrode recording side displaying a given EEG activity, either normal or abnormal.
Spread Propagation of EEG waves from one region of the brain to another.
Homologous Areas sharing common function. The same area on the opposite side or the same area having the same relative position in another organism.
Epileptic Focus The exact location of the brain from which an underling epileptiform discharge originates.
Asymmetry or Asymmetrical A change in the appearance of a rhythm on one side.
Symmetry or Symmetrical The same on both sides, patterns that appear the same over both hemispheres.
Polymorphic Multiple frequencies together creating complex waveforms.
Monomorphic Having one dominant pattern of rhythm.
Morphology The form or shape of EEG waves and patterns.
Biphasic A waveform having 2 phases or 2 deflections on each side of the baseline.
Sharp Wave A transient, usually negative in polarity but can be positive, with a duration of greater than 70 msec but less than 200 msec. Voltage is variable but usually is high. Morphology is sharply pointed.
Spike A transient with a duration of less than 70 msec but more than 20 msec and commonly (though not exclusively) negative in polarity.
Sinusoidal Having a curved shape as in an "S" or since wave.
Epileptiform Waveforms often associated with epilepsy such as spikes, sharp waves, or spike and slow wave.
Triphasic A waveform having 3 phases.
Electrodecremental An event causing sudden loss of amplitude with abrupt return to the previous pattern.
Organization The degree to which EEG rhythms conform to a certain ideal characteristic common to subjects in the same age group.
Complex A waveform made up of more than one frequency and morphology.
Suppression The attenuation of activity that should be there or is present on the opposite side such as in the suppression of alpha or sleep activity.
Artifact
Created by: akesselman