EEG

Electroencephalography

The process of amplification, recording

and analysis of the electrical potentials

of the brain.

Dura Mater-

The outer toughest layer of the meninges.

Arachnoid mater-

The web like middle layer of the meninges.

Pia Mater-

The innermost layer of the meninges.

Frequency -

Frequency is defined as cycles per second

The standard unit of frequency is “Hertz”

1 Hz is equal to 1 cycle per second.

The symbol for Hertz is “Hz”.

It is the number of complete cycles

of repetitive waves or complexes

in one second.

Cycles

-

A complete series of changes

undergone by a wave or complex

before the series of changes are

repeated.

Cycles per second -

Unit of frequency.

Also called Hertz

abbreviated “Hz”

Hertz

-

Unit of frequency. Cycles per second.

aka “Hz” Named for

Heinrich Randolf

Hertz,

a German physicist and pioneer

in radio communication. We capitalize

the abbreviation because it is a last

name.

Alpha

-

The frequency band in EEG that contains

frequencies from 8-13 Hz

Beta

-

The frequency band in EEG containing

faster frequencies 13 Hz to 30 Hz

Gamma

-

The frequency band in EEG containing

faster frequencies above 30 Hz

Delta

-

The frequency band in EEG containing

frequencies less than 4 Hz

Theta

-

The frequency band in EEG

containing frequencies from

4 Hz to less than 8 Hz.

Lateralized

occurring

only over one hemisphere

Bilateral

-

both sides, in EEG it means

occurring over bothhemispheres

Dominant Frequency

-

the

frequency of EEG activity

that occupies the greater part

of the recording.

Background Activity -

EEG activity representing normal

 patterns or the activity present in

abnormal patients during resting asymptomatic periods.

A normal patient will have a normal background

during resting wakefulness. An abnormal patient may have an abnormal background during resting wakefulness which may be slow or irregular but is their

resting basic rhythm.

Harmonic

-

A wave or frequency that is an integral multiple

of a given fundamental frequency. Harmonics

and subharmonics are seen in Photic driving

responses and sometimes in electrical noise

Sub-harmonic

-

Frequency that is below the fundamental

frequency, a frequency that divides evenly into the

fundamental frequency.

Photic driving

can be seen as a frequency that is a frequency equal

to or an integral submultiple of the photic frequency.

Harmonics & Sub-harmonics in Photic

Stimulation in EEG -

In EEG, during photic stimulation, photic driving can be at

the exact rate of the stimulation frequency, a multiple of

that frequency which is called a harmonic or a derivative

of that frequency which is called a sub-harmonic.

Alpha squeak

-

a transient increase in alpha frequency

immediately following eye closure.

Bancaud phenomenon

-

Uncommon unilateral failure of the alpha

to attenuate with eye opening. It may occur

in lesions of the temporal or parietal lobes.

Topography

refers to the distribution of a pattern or

waveform over the surface of the brain. In other words,

where is the pattern located? Is it frontal or anterior,

temporal, central, parietal, occipital or posterior,

lateralized on the left or right, focal, diffuse or

generalized?

Unilateral

 restricted

or remaining in one hemisphere

Contralateral

-

Relating to the opposite side of the head or body.

Ipsilateral

-

On the same side.

Focal

in

a clearly delineated area of the

brain as in a focal temporal spike

or focal slowing.

Multifocal

having

several independent foci as in

multifocal paroxysmal spike discharges

Generalized

occurring

simultaneously throughout the recording

electrodes. A discharge can be primarily generalized

(generalized from the onset) or secondarily

generalized (beginning focally and spreading to

become generalized).

Anterior

-

means at or

near the front

Posterior

-

at or near

the back

Diffuse

-

Widespread, occurring over large areas of

one or both hemispheres.

Focus

-

A limited region of the scalp,

cerebral cortex or depth electrode

recording site displaying a given

EEG activity, either normal or abnormal.

Foci

-

Plural of focus.

Multi-focal

-

Having two or more

spatially separated sites of origin.

Epileptogenic Focus-

The exact location of the brain

from which an underlying

epileptiform discharge originates.

Homologous

-

Areas sharing common function, the same

area on the opposite side or the same area,

having the same relative position, in another

organism.

Spread

-

Propagation of EEG waves from one

region of the brain to another.

Symmetry

or Symmetrical

the

same on both sides, patterns that

appear the same over both hemispheres,

there can be symmetry of frequency and

symmetry of amplitude.

Asymmetry or

Asymmetrical

-

a change in the appearance of a rhythm on one

side. The occurrence of or lack of a feature on one

side. An EEG can be asymmetrical because

of an

addition or suppression

of activity over one

side.

Morphology

-

The form or shape

of EEG waves and patterns.

Monomorphic

having

one dominant

pattern or rhythm

Polymorphic

-

multiple frequencies together

creating complex waveforms.

Spike

-

A transient with a duration of less

than 70 msec but more than

20 msec and commonly

(though not exclusively) negative in

polarity.

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.

Biphasic

a

waveform having 2 phases

or 2 deflections

on each side of the baseline

Triphasic

-

a waveform having 3 phases

Epileptiform

-

Waveforms often associated with

epilepsy such as spikes, sharp waves

or spike and slow waves.

Sinusoidal

-

having a curved shape

as in an “S” or a sine wave

“Alpha is often sinusoidal

in its morphology”

Complex

-

A waveform made up of more than one

frequency and morphology.

one example is: Spike and Slow Wave

Complexes the two waves form one

pattern but the two components are very

different in frequency and morphology.

Organization

-

The degree to which EEG rhythms

conform to a certain ideal characteristic

common to subjects in the same age group.

Electrodecremental

-

an event causing sudden loss of amplitude

with abrupt return to the previous pattern

Attenuation

-

Reduction in the amplitude of EEG activity

Artifact

-

Any potential difference

recorded due to an extracerebral

source recorded in an EEG record.

Examples: EKG, Pulse, EMG,

Eye movements, 60 Hz noise

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.

PLEDs

-

occurring in a variety of acute neurologic

conditions, most often with cerebral infarctions. Sharp

waves or sharp spiky complexes mixed with slower

frequencies occurring over one or both hemispheres

(BIPLED) Bilateral

I

ndependent Periodic Lateralized

Eplileptiform Discharges

“Spike Wave Discharges”-

epileptiform activity typically associated with seizure activity

.

Typical spike wave discharges are

3 Hz or 3/sec but atypical spike wave discharges can

range in frequency either slightly slower or slightly

faster. Can be focal, lateralized or generalized.

Build-up

Term used to describe the progressive increase

in voltage of the EEG or the appearance of waves

of increasing amplitude and sometimes a decrease in

frequency.

Burst

-

A group of waves which appear and disappear

abruptly and are distinguished from the

background activity by difference in frequency,

form and /or amplitude.

Burst-suppression

-

A pattern characterized by bursts of theta

and/or delta at times intermixed

with faster frequencies with intervening

periods of relative quiescence or flattening.

Syncope

-

Episodic loss of consciousness,

a spell, swoon or faint.

Anoxia

-

Deficiency of oxygen in the blood

.

Hypoxia

-

Condition in which there is a decrease

in the oxygen in the blood.

Symptoms of generalized hypoxia depend on the

severity and speed of onset and include

headaches, fatigue, shortness of breath,

nausea, unsteadiness, seizures and coma.

Apnea

-

Breathing disorder during sleep causing

cessation of breathing.

Sleep apnea is either central or obstructive.

In central apnea there is no abdominal effort

and in obstructive apnea there is effort but

there is restriction of airflow in the airway.

Hypopnea

-

Abnormal decrease in the depth

and rate of breathing.

Insufficient breathing.

Ischemia

-

A restriction in the blood supply

generally due to factors in the

blood vessels with resultant

damage or dysfunction of tissue

supplied by the blood vessels.

Agnosia

-

An inability to recognize objects or have knowledge

(gnosia)of objects through the senses.

Stereognosis

-

The ability to have knowledge (gnosia)

of the solidness (stereo) of an object

using the sense of touch.

Example: the ability to tell the different

thickness of an object,

like a dime and a nickel by feeling them.

Bruxism

-

Habitual purposelessgrinding of the teeth

Apraxia

-

Inability (a)to perform

certain actions (praxia)

Chorea

-

Ceaseless rapid jerky movements

that may appear to be

well coordinated like dancing.

Coma

-

A state of unconsciousness from which a

person cannot be aroused. The person is

called “comatose.”

Concussion

-

An injury caused by a

violent shaking of the brain.

Confusion

-

A state of mind in which several facts are

blended (fuse) with (con)

each other and a person is unable

to distinguish one fact from the other.

Dyskinesia

-

Difficulty (dys) in performing voluntary

muscular movements (kinesia).

Ataxia

-

Unsteadiness, loss of (a)

muscle coordination (taxia).

Sensory ataxia - loss of coordination

due to feeling, especially the sensation of

position and movement.

Neuralgia

-

Pain (algia) along the course

of a nerve (neur).

Neuritis

inflammation

(itis) of a nerve (neur).

Opthalmoplegia

paralysis

(plegia) of the eye (opthalmo).

Paralysis

-

Loss of muscle function caused by injury

or disease of the nerves, brain or spinal cord.

The muscles “

appear

to be cut” (lysis)

on one side (para) of the body

Paresis

-

Slight or incomplete paralysis;

muscle weakness. The muscles

appear to be in a state of relaxation.

Paresthesia

-

An abnormal sensation (esthesia) such

as numbness or tingling , around

(par, variation of para) a part.

Aphasia

-

Loss (a) of the ability to speak (phasia)

Broca’s Aphasia-

Expressive Aphasia, Damage to the frontal lobe

causes inability to express themselves well with

spoken words. Often accompanied by right sided

weakness or paralysis of the arm and leg. Patients

with Broca’s aphasia may speak

with great effort in very short and incomplete

sentences, their understanding of speech is usually

intact.

Wernicke’s Aphasia-

Receptive Aphasia, Damage to the temporal

lobe causing inability to understand speech

and often difficulty expressing themselves as

well. Patients with Wernicke’s aphasia may

speak in long complex sentences that make

little or no sense.

Global Aphasia-

The result of damage to extensive

portions of the language areas of the brain,

causing extreme communication difficulties

limiting the ability to speak and

comprehend language.

Dementia-

Deterioration of intellect.

Photophobia

-

Dislike of the light.

A common complaint

of migraine patients.

Scotoma

-

A patch of blindness. An area of loss

 or impairment of visual acuity

surrounded by a field of normal or

 relatively preserved vision. It can

appear as a spot anywhere in the

 visual field or as a peripheral ring

causing tunnel vision as in retinitis pigmentosa.

Infarct or Infarction

-

An area of brain tissue deprived of

 blood supply resulting in

death of tissue. Infarctions can be caused by thrombosis,

ischemia or embolus such as dislodged atherosclerotic

plague. An infarction can cause focal

slowing on the EEG and possibly PLEDs or other

epileptiform discharges.

Tinnitus

-

Ringing in the ears.

Tic

-

A recurrent spasm

Stupor

-

When a person is near unconscious

but can be aroused, an acute lack of

mental alertness induced by drugs,

alcohol, shock, head injury, or extreme

lack of sleep

Quadriplegia

-

Paralysis of all 4 limbs.

Paraplegia-

Paralysis of both legs.

Papilledema-

Swelling of the optic disc.

A sign of increased intracranial

pressure although the absence of

papilledema does not exclude

increased intracranial pressure.

The optic disk is the optic nerve

head where the ganglion cell axons

exit the eye to form

the optic nerve.

Nystagmus-

Rapid involuntary rhythmic eye movements

characterized by a slow drift in one direction

and a rapid movement in the

opposite direction.

Babinski’s Sign

The plantar reflex response also called the

Babinski reflex. Upon stroking the lateral

portion of the bottom of the foot, the toes

should all flex or curl downward, extension

of the great toe upward and fanning of the

other toes is normal in infants but in all other

patients is an abnormal response indicating a

lesion in the central nervous system.

Cafe-au-lait patches -

Brown patches on the skin seen in

Neurofibromatosis.

Burr Hole-

A hole drilled in the skull. When recording

EEG the amplitude over or near a Burr

hole will increase due to the absence of

the skull as a buffer.

This is called a “Breach Rhythm”

since it is the breach in the skull

which allows more amplitude to be recorded

Comatose

a profound

state of unconsciousness in which the patient

is unable to awaken and fails to respond

normally to pain, light or sound, but does not

have normal sleep patterns on EEG and does

not have voluntary movements. Can result

from metabolic and toxic conditions, stroke,

hypoxia, and head injuries. Coma can be

induced with drugs.

Scintillating Scotoma-

The sensation of a luminous appearance

before the eyes, with a zigzag, wall like

outline. Often in the shape of an arc or

crescent.

Called also fortification spectrum, or

flittering scotoma

Todd’s Paralysis

Post-epileptic hemiplegia

lasting for a few minutes or hours

to three or four days, or even longer,

after the epileptic seizure.

Contrecoup

“Counterblow”, injury resulting from

a blow to another site. A blow to one side

of the head may cause an injury to the brain

on the opposite side of the head,

as the brain moving freely within the skull,

abruptly is thrown against the opposite side

of the interior of the skull.

Aura

A precursor or warning to an epileptic

seizure, experienced by the patient.

Often arising from the temporal

lobe these sensations include,

“deja vu”, “jamais vu”

, visual or auditory

hallucinations, sensations of fear,

or arising from the uncus,

unpleasant odors or tastes.

Deja-vu

The feeling of familiarity

in a new situation that is

sometimes an aura (precursor warning)

to an epileptic seizure.

Jamais vu

A “sense of strangeness” when in familiar

surroundings. Opposite of deja vu.

This is a common aura of a temporal lobe

seizure.

Tonic-clonic Seizures-

(

formerly called Grand Mal Seizures)

A generalized convulsion, the tonic phase is stiffening

and extension of the body and clonic phase is

rhythmic jerking.

Absence seizure-

(formerly called Petit Mal Seizures)

Typically the EEG shows 3 Hz spike and

wave complexes. The clinical

manifestations may be slight with eye

flutter, head nodding and brief

impairment of consciousness.

Myoclonic Seizures-

The EEG consists of polyspikes or polyspike and

slow wave discharges which are bilateral or

generalized and synchronous, usually maximal in the

frontal areas. Clinically there is rapid involuntary

muscle contraction either subtle or massive. Some

myoclonus may be nonepileptic.

Encephalitis

-

Inflammation of the brain.

itis = inflammation

encephal = brain

Encephalopathy

-

General term meaning a disease (pathy) of the

brain (encephalo).

Seizure

-

A sudden attack or recurrence of convulsions,

temporary loss of consciousness without convulsions,

alterations of consciousness, or motor or sensory

events caused by abnormal electrical activity of a group

of brain cells.

Seizures can cause involuntary changes in body

movement, function, sensation, awareness or behavior.

Status epilepticus -

A continuous seizure that will not stop

without intervention.

Epilepsy

-

A disorder of recurrent seizures.

One seizure does not “Epliepsy” make.

Narcolepsy

a

disorder in which a person is seized (lepsy) by

the sudden urge to sleep (narco).

Cataplexy

-

Sudden episodes of loss of muscle function, ranging from

slight weakness (such as limpness at the neck or knees,

sagging of facial muscles or inability to speak clearly) to

complete body collapse. Attacks may be triggered by

emotional reactions such as laughter, anger or fear and may

last from seconds to several minutes. There is no loss of

consciousness. Cataplexy is unique to narcolepsy.

Sleep Paralysis-

Temporary inability to talk or move

when falling asleep or upon waking up.

Lasts a few seconds to several minutes.

Hypnagogic Hallucinations

-

Vivid often frightening , dreamlike experiences that

occur while dozing, falling asleep or upon waking.

While partially awake and partially asleep,

characters from the dream state may appear as

hallucinations. The patient experiences a partial dream

and partial wake state.

Hydrocephalus

-

An increase in the accumulation of

cerebrospinal fluid (hydro)

within the ventricles

of the head (cephalus).

Meningioma-

A benign tumor growing from the arachnoid.

Meningitis-

Inflammation of the meninges.

Meningocele-

A bulge in the meninges through a

breach in the bony coverings.

Meningoencephalitis-

Inflammation of the meninges and brain.

Aneurysm

-

A weak bulge in an artery wall, prone to

rupture and cause a hemorrhage. It can be

corrected with neurosurgery using a clip.

Migraine-

Periodic, throbbing, severe,

frequently unilateral headaches.

Photophobia (sensitivity to light),

and phonophobia (sensitivity to sound)

are common as well as nausea and

vomiting. There may be an aura

of visual fortification spectra,

scintillating scotomas or flashes of light.

Lennox-Gastaut Syndrome-

A syndrome composed of more than one type of

seizure, often including atonic seizures, an EEG finding

of slow spike and wave complexes from 1 to 2.5 /sec

and sometimes runs of rapid spikes.

The background can be disorganized and excessively

slow or sometimes unremarkable .

Most patients are not responsive to treatment.

Mental handicap in Lennox-Gastaut Syndrome

ranges from the most profound to the slightest degree.

TIA

Transient

Ischemic Attack-

An acute neurologic deficit of vascular origin

that clears completely. Can last minutes to

hours but not more than 24 hrs

Stroke

Most frequent expression of cerebrovascular

disease, sudden and severe focal onset of

neurological deficit of vascular origin caused by

emboli, thrombosis or hemorrhage, lasting

more than 24 hrs.

Embolism

-

The sudden blocking of an artery or a

vein by a clot or obstruction which has

been brought to its place by blood

current.

Thrombus

A clot or plug in a blood vessel

formed by coagulation and remaining at the

point of its formation.

(unlike an embolus, which travels)

Hemorrhage

-

Literally, “to burst forth”. A copious

escape of blood from the vessels,

bleeding.

Infantile Spasms-

Also known as “jack-knife attacks”

a type of seizure in infants, consisting of

sudden tonic and myoclonic spasms with

massive flexion of the head, trunk and

extremities. This type of seizure is

associated with the EEG pattern of

Hypsarrhythmia.

Benign Rolandic Epilepsy (BRE)

ALSO CALLED 

 Benign Epilepsy Central-Temporal Spikes (BECTS) 

 Benign Rolandic Epilepsy of Childhood (BREC)-

Occurring in children with central sharp

waves or spikes, and sometimes but not always

associated with seizures.

When associated with seizures, they are either

focal motor or generalized tonic-clonic seizures

and the seizures have a high incidence

of resolving with age, hence the name “benign”.

Sagittal

-

relating to or situated on the

imaginary plane that divides a

human or animal body into right

and left halves