Electroencephalography (EEG): an electrophysiological monitoring method to record electrical activity of the brain.

School of Nursing & Midwifery
Department of Adult Health Nursing
P.by: Habtemariam Mulugeta
College of Medicine &
Health Sciences
1
Habtemariam M. 11/25/2020

PREPARED BY: HABTEMARIAM MULUGETA
SGSR 398/12
2
ADVANCED ADULT HEALTH
NURSING – II
Electroencephalography (EEG)
Habtemariam M. 11/25/2020

Presentation Outline
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 Objectives
 Anatomy & physiology review
 Introduction
 Components of EEG
 Electrode Placement system
 Montage
 Interpretation
 Summary
 References
 Acknowledgment
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Objectives
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 Within the entire sessions all learners will:
 Familiarize with the principles of techniques involved in EEG
 Count frequencies & measure the amplitudes of the record obtained.
 Categories the records into appropriate rhythms – α, β, θ & δ.
 Appreciate clinical use of EEG.
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Review of Anatomy & Physiology of
Nervous System

Nervous System
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Central Nervous System
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Cont.
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The Brain
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 The human brain is the main
organ of human CNS.
 On average, it weighs about 1.4
kg (≈ 2% of total body weight).
 volume of around 1260 cm3 in
men & 1130 cm3 in women.
 100 billion neurons
 100 million billion connections
between neurons
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Major Regions of the Brain
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1. Cerebrum
2. Cerebellum
3. Brainstem
4. Limbic System
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The Cerebellum
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 The Cerebellum (meaning “little brain“) has two
hemispheres which have highly folded surfaces.
 It contributes to regulation & control of fine movements,
posture & balance.
 It receives input from sensory systems of the spinal cord
& from other brain areas & integrates these inputs to fine-
tune motor activity.
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The Brainstem
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 It is the lower & oldest part of the brain, comprising the
midbrain, pons & medulla.
 Often called the reptilian brain.
 10 of the 12 pairs of cranial nerves emerge directly from it.
 It controls autonomic body processes such as heartbeat,
breathing, bladder function & sense of equilibrium.
 Basically, it controls everything that is automatic work without
having to conscious thinking.
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The Limbic System
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 It is often referred to as the emotional brain.
 It is buried deep within the brain.
 The limbic system includes the hippocampus, thalamus,
hypothalamus & amygdala.
 The limbic system plays a central role in arousing fight-
or-flight situations.
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The Cerebrum
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 It is the forward-most portion & largest part of the human brain.
 It is generally associated with higher brain functions such as
conscious thought & sensory processing.
 It consists of two hemispheres which are connected through a
mass of nerve cells making up the corpus callosum.
 It is further divided into 4 sections, the lobes: Occipital, temporal,
parietal & frontal.
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Cont.
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Cont.
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The Occipital Lobe
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 It is the visual processing center of our brain.
 It including low-level visuospatial processing (orientation,
spatial frequency), color differentiation & motion perception.
 It is located in the rearmost portion of the skull.
 Occipital lesions are typically associated with visual
hallucinations, color or movement agnosia as well as
blindness.
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The Temporal Lobe
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 It is associated with processing sensory input to derived, or
higher, meanings using visual memories, language &
emotional association.
 It is responsible for long-term memory.
 The left temporal cortex is involved in the comprehension of
written & spoken language (Wernicke’s area).
 Damage to these regions causes deficits in talking (Wernicke’s
aphasia).
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The Parietal Lobe
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 Integrate information from external sources & internal sensory feedback into
a coherent representation of how our body relates to the environment, & vice
versa.
 It used for Tasks requiring eye or hand movements & eye-hand coordination.
 It also processes, stores & retrieves the shape, size & orientation of objects
to be grasped.
 Damage in parietal cortex cause severe disruptions in motor behavior &
object-oriented actions as well as out-of-body experiences.
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The Frontal Lobe
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 It is the region where most of conscious thoughts & decisions are made.
 It also contains motor areas where voluntary movements of all of our
limbs & eyes are controlled.
 It contains most of the dopamine-sensitive neurons.
 It is the core centers of our personality.
 Frontal lobe lesions cause severe changes in personality & taste
preferences, pro-social behavior, & action control.
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Cont.
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Peripheral Nervous System
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Cont.
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Neurons
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 Are the basic structural unit of the nervous
system
 Are specialized for impulse conduction
 Has three major parts:
 Dendrites: carry impulses towards the cell
 Cell body: contains the nucleus & other
organelles important for protein synthesis
 Axon: carry impulses away from the cell
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Cont.
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 There are about 100 billion neurons in the human brain
 They carry out communication in the brain.
 There are also billions of other cells that carry out a range
of functions to both support, nurture, & facilitate neural
signaling (among other functions)
 The site where two neurons or an neuron & an effector cell can
communicate is termed a synapse.
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Structural Classification of Neurons
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 According to the number of processes extending from the cell body
1. Multipolar neurons: usually have several dendrites & one axon
 E.g. Most neurons in the brain & spinal cord
2. Bipolar neurons: have one main dendrite & one axon
 They are found in the retina of the eye, in the inner ear & in the olfactory area of
the brain
3. Unipolar neurons
 These neurons are more appropriately called Pseudounipolar Neurons
 Have short single process that branches like a T.
 E.g. Sensory neurons
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Cont.
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Neural activation & electrical fields
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 Synapses act as gateways of inhibitory or excitatory activity
between neurons.
 Synapses propagate information impulses across neurons that:
 either increases the chance of the subsequent neuron signaling (excitatory)
 or decreases the chance of the subsequent neuron signaling (inhibitory).
 Synaptic transmission triggers the release of neurotransmitters
(dopamine, epinephrine, acetylcholine, etc), which can cause a
voltage change across the cell membrane.
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Cont.
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 Synaptic activity often generates a subtle electrical field, which is
also called a postsynaptic potential.
 Postsynaptic potentials typically last 10s to 100s of milliseconds.
 The postsynaptic potential of a single neuron is too tiny to even be
noticed.
 Yet, if there’s several of them happening at the same time, in the
same location, & in the same rhythm, they all add up be noticeable.
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Cont.
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 Not all electrical fields generated by the brain are strong enough
to spread all the way through tissue, bone & skull towards the
scalp surface.
 Research indicates that it is primarily the synchronized activity of
pyramidal neurons in cortical brain regions which can be
measured from the outside (i.e. from EEG devices).
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Cont.
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Cont.
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Cont.
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 Pyramidal neurons always oriented perpendicular to the
cortical surface.
 This unique orientation of the cells generates an
electrical field with a very stable orientation.
 By contrast, cells in deeper brain structures (such as the
brain stem or cerebellum) don’t have this specific
orientation.
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Cont.
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 As a result, the electrical fields are spread into various
directions & cancel out instead of projecting in a stable
way towards the scalp surface.
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Introduction to EEG
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 Electroencephalography (EEG) is an electrophysiological monitoring
method to record electrical activity of the brain.
 It is typically noninvasive, with the electrodes placed along the scalp,
although invasive electrodes are sometimes used, as
in electrocorticography.
 EEG measures voltage fluctuations resulting from ionic current within
the neurons of the brain.
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History
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RICHARD CATON , 1874
First person to record electrical activity from
animal brain in 1874.
German physiologist & psychiatrist HANS BERGER
(1873–1941) recorded the 1st human EEG in 1924.
Expanding on work previously conducted on animals by
Richard Caton & others.

Cont.
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 Berger also invented the electroencephalogram.
 In 1934, Fisher & Lowenback first demonstrated
epileptiform spikes.
 In 1947, The American EEG Society was founded & the
1st International EEG congress was held.
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Cont.
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Cont.
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Mechanism Of EEG
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 The billions of nerve cells in the brain produce very small
electrical signals that form patterns called brain waves.
 During an EEG, small electrodes & wires are attached to
the head.
 The electrodes detect brain waves
 EEG machine amplifies the signals & records them in a
wave pattern on graph paper or a computer screen.

Factor influencing EEG
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 Age
 Infancy – theta, delta wave
 Child – alpha formation.
 Adult – all four waves.
 Level of consciousness (sleep)
 Hypocapnia(hyperventilation) slow & high amplitude waves.
 Hypoglycemia
 Hypothermia
 Low glucocorticoids
Slow waves

Indications
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1. Diagnosis:
 NCSZs & NCSEs are
common in critically ill
patients.
 Brain Death
 Delayed Cerebral Ischemia
post subarachnoid
hemorrhage.

Cont.
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2. Titration of Treatment (Rx):
 Rx of NCSE: sedative medications (midazolam, propofol, ketamine &
barbiturates) are increased until the EEG shows either:
 Resolution of the seizures
 Brust suppression
 Rx of refractory high ICP: after exhaustion of other therapies for elevated ICP
sometimes patients are treated with a barbiturate coma, where barbiturates are
dosed at a level that achieves burst suppression on EEG & ICP < 20.
 A continuous EEG is used to help find the right level of anesthesia for someone in
a medically induced coma.

Cont.
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Cont.
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3. Prognostication:
 EEGs can be used to assist with prognosticating patients with certain
neurologic disorders including:
 Hypoxic – Ischemic Encephalopathy
 Subarachnoid Hemorrhage
 Traumatic Brain Injury

General Applications
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 Monitor alertness, coma & brain death.
 Locate area of damage following head injury, stroke,
tumor etc.
 Test Afferent Pathways
 Monitor cognitive engagement (alpha rhythm)
 Control anesthesia depth
 Investigate epilepsy & locate seizure origin

Cont.
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 Test Drug effect on epilepsy or convulsion
 Assist in experimental cortical excision of epileptic focus
 Monitor human & animal brain development
 Investigate sleep physiology & disorder
 EEG can't measure intelligence or detect mental
illness.

Contraindications
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 Only relative contraindications:
Raised intracranial pressure
Recent MRI (<3 month)
Retinal detachment
Pheochromocytoma
Anesthetic risk

EEG RISK
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 EEGs are safe & painless.
 Sometimes seizures are intentionally triggered in people
with epilepsy during the test, but appropriate medical care
is provided if needed.

Pros of EEG
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 Non - invasive
 Harmless
 Lower costs
 Portable
 High temporal resolution

Cons of EEG
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 High noise/artifact ratio
 Not very exact measuring
 Skull weakens the electrical activity
 Low spatial resolution

Components Of EEG
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1. Electrodes: Small, non-reactive metal discs or cups applied to
the scalp with a conductive paste.
 Made up of Gold, silver/silver chloride, tin, & platinum
 Each electrode site is labeled with a letter & a number.
 Placed on the scalp in special position these position is
specified using the international 10/20 system commonly.

Cont.
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 Electrode contact must be firm in order to ensure low impedance.
 Types of electrode:
1. Disposable electrode (gel-less, pre gelled)
2. Re-usable disc electrode (Au, Ag/AgCl, tin, & platinum)
3. Headband electrode
4. Cap electrode
5. Saline based electrode
6. Needle electrode

Cont.
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Cont.
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1. EEG electrodes placed
separately on scalp.
2. EEG electrodes mounted
as special band on head.

Cont.
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 active electrodes placed on the scalp using a conductive
gel or paste.
 Signal-to-noise ratio (impedance) reduced by light
abrasion.
 Can have 21, 32, 64,128, 256 electrodes.
 More electrodes = richer data set.

Cont.
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2. Amplifier: is an electronic device that increases the power of a
signal.
 Brainwave activity is too subtle to read unless the signal is amplified.

Cont.
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 Differential Amplifiers have two important roles:
1. Differential discrimination: Amplifier reject voltage that are
common to both inputs within a channel (Presumed to be non
cerebral in origin, i.e. artifact/noise)
2. Amplification of the remaining voltage: by 1 million times.

Cont.
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Cont.
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3. Filters: is an indispensable tool in
producing interpretable EEG
tracings.
 Without it, many segments of EEG
would be essentially unreadable.
 Its main benefit is that it can
“clean up” the EEG tracing,
making it easier to interpret &
generally more pleasing to the eye.

Cont.
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 Filters attenuate waveforms of relatively High (>30Hz) &
Low (<1Hz) frequency which are presumed to be non
cerebral origin (i.e. artifact).
 This allows waveforms of cerebral origin to be recorded
clearly with out distortion.

Cont.
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 There are three types of filters:
1. High Frequency Filters: attenuate high frequency signals &
allow low frequency signals to pass.
2. Low Frequency Filters: attenuate Low frequency signals &
allow high frequency signals to pass.
3. Notch Filter: eliminate current of specific frequency.
 In North America the Notch filter that is used is a 60Hz filter which
attenuates all signals of 60Hz (standard current in North America)

Cont.
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4. Writing unit: is the final link between
the patient & a legible EEG tracing.
 A pen-ink-paper system is employed.
 The speed of the paper mechanism
should include 30 mm/s with at least the
additional speeds of 15 mm & 60 mm/s
selectable during operation.
 NB: The writing unit may be replaced by a
digital screen in modern EEG devices.

Analog to Digital Converter
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 Found in Modern EEG device which uses complicated
mathematical concepts.
 Convert Analog to Digital
 Conventional analogue instruments consist of an amplifier, a
galvanometer (a coil of wire inside a magnetic field) & a writing
device.
 Digital EEG systems convert the waveform into a series of
numerical values, a process known as Analogue-to-Digital
conversion.

Cont.
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EGG Techniques
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 resting EEG - Multichannel recording of eyes-closed, a sample
of artifact-free data analyzed.
 aka Routine/Spot EEG (rEEG)
 Performed for the duration of 20 – 30 minutes & longer if
necessary.
 Can be useful when screening for patients with or at high risk
for NCSZs, & for neuro-prognostication purposes.

Cont.
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 continuous EEG (cEEG)
 Ensure prompt diagnosis & proper management of NCSZs & NCSEs.
 To monitor for delayed cerebral ischemia in patients with
subarachnoid hemorrhage, & for tittering burst suppression therapies
(e.g. Barbiturates) in patients with refractory high ICP.

Cont.
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 Ambulatory EEG (aEEG)
 relatively recent technology that allows prolonged EEG recording in the home
setting.
 less expensive alternative to inpatient monitoring, with costs that are 51-65%
lower than a 24-hour inpatient admission for video/EEG monitoring.
 Used for Confirmation of clinical suspicion of epilepsy in patient is
experiencing daily or almost daily spells.
 the diagnostic yield of AEEG indicate that 6-15% of AEEGs record seizures.

Cont.
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Ambulatory EGG

Cont.
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 Video EEG/Video telemetry - Simultaneous recording of brain
activity on an EEG & behavior on tape or digital video.

Cont.
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 Q-EEG/BEAM/Brain Mapping/rEEG
 resting EEG - analyzed using the Fast Fourier Transform
(FFT) to quantify the power at each frequency of the EEG
averaged across the entire sample, known as the power
spectrum.
 QEEG findings are then compared to a normative database

Cont.
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 Color density Spectral Array (CDSA): aka FFT
Spectrogram which convert raw EGG data into 3D plots
with time in X axis. Frequency in Y axis & EEG power in
Z axis.

Cont.
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Cont.
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 Polysomnography - Simultaneous recording of:
 Brain waves (EEG)
 Eye movement
 Heart rate (ECG)
 Breathing rate
 Blood oxygen level
 Positioning of body
 Movement of limbs
 Sounds made while sleeping

Electrode Placement System
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 Skull is taken in three planes – sagittal, coronal, & horizontal.
 The summation of all the electrodes in any given plane will equal
100%.
 Electrodes designated with odd numbers are on the left; those
with even numbers are on the right.
1. 10-20 international system
2. 10-10 international system

10-20 international system
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 It is an internationally recognized method that allows
EEG electrode placement to be standardized.
 The 10-20 system is based on the relationship between the
location of an electrode & the underlying area of cerebral
cortex.

Cont.
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 Each site has a letter & a number or another letter to
identify the hemisphere location.
 The letters F, T, C, P, & O stand for Frontal, Temporal,
Central, Parietal & Occipital.
 Even numbers (2,4,6,8) refer to the right hemisphere
 Odd numbers (1,3,5,7) refer to the left hemisphere.
 The z refers to an electrode placed on the midline.

Cont.
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 Four Skull Landmarks:
 Nasion (Nz): the depression between the eyes at the top of the nose.
 Inion (Iz): the bump at the back of the head.
 Left & right preauricular points: the depressions just anterior to the ears,
It felt with our fingers when we open & close our mouth.

Cont.
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Cont.
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Cont.
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 Measuring FPz or Reference Electrode:
 Measure the distance from nasion to inion
 measure 10% of all distance from nasion & mark for
Reference electrode in the front.
 Measuring Oz:
 Measure the distance from nasion to inion
 measure 10% of all distance from inion & mark for Oz in the back.

Cont.
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 Measurement of CZ:
Measure the distance from FPz to Oz & divide/ 2 = CZ
 Measurement of FZ:
Measure the distance form CZ – Ref
Divide by 2 = Fz
 Measurement of PZ :
Measure the distance from Cz – Oz divide / 2 = PZ

Cont.
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Cont.
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 Measurement of FP1 & FP2:
Measure the distance head circumference & take 10% of all
measurement divide / 2 mark it:
On left side for FP1
On right side for FP2
 Measurement of F7 & F8:
Measure the distance head circumference & take 10% of all
measurement
Mark 10% by measuring for every led

Cont.
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 Measurement of T3 & T4:
 Measure the distance between pre – auricular points & cross Cz
 Mark 10% of the distance from left & right pre – auricular points
of ears.
 Left for T3
 Right for T4

Cont.
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 Measurement of T5 & T6:
 Measure the distance head circumference & take 10% of all
measurement
 Mark 10% by measuring for every led
 FPz 10% F7 10% T3 10% T5 10%
 FPz 10% F8 10% T4 10% T6 10%

Cont.
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 Measurement of F3 & F4:
 Measure the distance from F7 - Fz / 2
 Mark on the left forF3
 Mark on the Right forF4

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 Measurement of C3 & C4:
 Measure the distance form CZ – T3 / 2 =C3
 Measure the distance form CZ – T4 / 2 = C4
 Measurement of P3 & P4:
 Measure the distance from T5 – PZ / 2
 Mark on the left forP3
 Mark on the Right forP4

Cont.
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 Measurement of O1 & O2:
 Measure the distance head circumference & take 10% of all
measurement mark it:
 On Left side for O1 = T5 10% = O1
 On Right side for O2 = T6 10% = O2

Cont.
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Cont.
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Cont.
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10-10 international system
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 Also known as modified version of the basic 10-20
system.
 About 75 electrodes used
 More accurate than 10-20 system
 It is not typically used in routine recordings but may be
used in special circumstances.

Cont.
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American Clinical Neurophysiology Society Guideline 5: Guidelines for Standard Electrode Position Nomenclature. J Clin Neurophysiol
2:107–110, 2006.

10-20 Vs. 10-10
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Ground Electrode
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 It is used for common mode rejection.
 Primary it prevent power line noise from interfering with the
small biopotential signals of interest.
 By design, amplifiers should not be affected by large changes
in potential at both the active & reference sites.
 A ground electrode for EEG recordings is often placed on the
forehead (but could be placed anywhere else on the body; the
location of the ground on the subject is generally irrelevant).

Electrode Impedance
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 Signal-to-noise ratio (impedance) is measure of the
impediment to the flow of AC, measured in ohms at a
given frequency.
 Larger numbers mean higher resistance to current flow &
the smaller the amplitude of the EEG signal.
 In EEG studies, should be at lest 100 Ω or less & no more
than 5 kΩ.

Montage
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 Montage refers to the order & choice of channels displayed on
the EEG page.
 It denotes the particular combination of electrodes examining
at a particular point of time.
 It is the Different sets of electrode arrangement on the scalp by
10 – 20 system.
 21 electrodes are attached to give 8 or 16 channels recording.

Cont.
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 Based on the technique by which EEG data are displayed
Montage generally divided into two large groups:
Referential Montage
Bipolar Montage

Referential Montage
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 When a single reference point is used for all electrodes.
 Connects active scalp electrodes & an inactive electrode placed
away from the scalp
 e.g. on ear, nose or chin [Reference electrode]
 Useful for seeing amplitude of waves
 Disadvantage
 with ear- some brain activity
 Chin & nose- heart activity

Cont.
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Referential Montage

Cont.
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Cont.
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 There are two general strategies for channel arrangement.
1. left–right pairs so that each position on the brain can be
compared with its homologous counterpart in the opposite
hemisphere.
 “left–right–left–right. . .” arrangement of channels (e.g. Fp1 followed by
Fp2, F7 followed by F8, F3 followed by F4, & so on).
2. “left-over-right” & “front-to-back”: channels are “clumped”
according to their location

left–right pairs
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“left-over-right” & “front-to-back”
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Average Reference montage
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 Activity from all electrodes is measured, summed & then
averaged.
 The resulting signal is then used as a reference electrode & acts
as input 2 of the amplifier.

Laplacian montage
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 each channel represents the difference between an
electrode & a weighted average of the surrounding
electrodes.
 Extremely helpful in detecting focal abnormality on
EEG & electrographic seizure topography

Cont.
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Commonly used reference points
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 Earlobes
 share a portion of the electrocerebral activity present in the
adjacent midtemporal areas, causing a cancellation effect.
 This makes an earlobe reference a poor choice for a patient
with a high voltage midtemporal discharge.
 left earlobe contaminated with EKG artifact because of the
left-sided position of the heart.

Cont.
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 “Virtual” reference electrode
 complex reference
 the arithmetic mean of some or all of the scalp electrodes
 Nose Reference: may be contaminated by a surprising amount of
muscle artifact

Cont.
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 The cervical area
 muscle artifact or EKG signal
 Artifact of movement when patients are lying on their backs.
 The midline vertex electrode, Cz,
 free of muscle artifact due to its location at the vertex of the scalp
 contains a large amount of electrocerebral activity, especially
during sleep therefor rarely used.

Bipolar Montage
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 When several referential points are used for recording.
 Each channel is attached to two different electrodes
 The electrodes form a chain passed side by side or front to back.
 Mostly used in Practice by electroencephalographers.
 preferred because it produce “cleaner” tracings due to the
proximity of the electrode pairs, which leads to more efficient
noise cancellation.

Cont.
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 Disadvantage
 It may actually cancel out some of that common brain wave activity, that we
actually seek to record.
 larger interelectrode distances are associated with higher voltages, &
smaller interelectrode distances are associated with lower voltages
 There are two principal categories of bipolar montages:
 the anteroposterior (AP) bipolar montage
 the transverse bipolar montage

Anteroposterior (AP) bipolar montage
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 electrode chains run from front to back (anteroposteriorly) down
the head
 helps see progression of waves
 indicate the maximum of the discharge in the front-to-back
direction

Cont.
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 Also known as Longitudinal Bipolar Montage, Double
Banana Montage
 Best for analyzing low - to medium - amplitude waveforms
that are highly localized
 Alternate front & back electrodes
 localize the maximum of the discharge in the front-to- back
direction.
 Most commonly used for EEG interpretation

Cont.
116
Longitudinal Bipolar Montage

Cont.
117

Transverse bipolar montage
118
 The electrodes form a chain run from left to right (transversely)
across the head
 Alternate left & right electrodes - helps compare the two sides
 localize the maximum of the discharge in the left-to-right direction.

Cont.
119
 large majority of discharges seen in an AP bipolar montage
will also be visible in a transverse bipolar montage.
 However, there are exceptions, Certain discharges may show a
steep gradient in the AP direction & a shallow gradient in the
transverse direction (or vice versa).
 Combining the two techniques allows localization of the
maximum on a two-dimensional model of the scalp surface

Cont.
120

Circumferential Bipolar Montages
121
 makes a complete circumference around the head.
 also known as a halo, circumferential, or hatband montage
 almost every pairing is present in the standard AP bipolar
montage but the Fp1-Fp2 & O1-O2 pairs are unique to it.
 Fp1-Fp2 & O1-O2 pairs are included in the transverse bipolar
montages, therefore it is not a mandatory member of a
laboratory montage set.

Cont.
122

Variables used in the classification of EEG activity
123
 Frequency: the number of oscillations per second & has
the unit Hertz (Hz).

Properties of EEG frequency
124
 Rhythmic: EEG activity consisting in waves of
approximately constant frequency.
 Arrhythmic: EEG activity in which no stable rhythms
are present.
 Dysrhythmic: Rhythms &/or patterns of EEG activity
that characteristically appear in patient groups or rarely
seen in healthy subjects.

Morphology
125
 Morphology: refers to the shape of the waveform.
 It is determined by the frequencies that combine to make
up the waveform & by their phase & voltage
relationships.

Wave patterns Description
126
1. Monomorphic: Distinct EEG activity appearing to be composed of one dominant activity
2. Polymorphic: distinct EEG activity composed of multiple frequencies that combine to
form a complex waveform.
3. Sinusoidal: Waves resembling sine waves. Monomorphic activity usually is sinusoidal.
4. Transient: An isolated wave or pattern that is distinctly different from background
activity.
a) Spike: a transient with a pointed peak & a duration from 20 to under 70 msec.
b) Sharp wave: a transient with a pointed peak & duration of 70-200 msec.

Cont.
127
 Synchrony
 It refers to the simultaneous appearance of rhythmic or morphologically
distinct patterns over different regions of the head, either on the same side
(unilateral) or both sides (bilateral).
 Periodicity
 It refers to the distribution of patterns or elements in time (e.g., the
appearance of a particular EEG activity at more or less regular intervals).
 The activity may be generalized, focal or lateralized.

Cont.
128
 Amplitude: is the voltage or power seen in a signal.
 Voltage: refers to the average voltage or peak voltage of
EEG activity.

Cont.
129
 Measured: peak to peak
 Expressed as range i.e. 40-50μv
 Depends on
 Inter electrode distance
 Type of montage
 Type of recording
 Surface (10-100 μv)
 Depth (500-1500 μv)

EFFECT OF MONTAGE ON AMPLITUDE
130
Referral (Ipsilateral ear) Bipolar

Descriptive terms associated with EEG voltage
131
1. Attenuation (synonyms: suppression, depression): Reduction of amplitude of
EEG activity resulting from decreased voltage.
 When activity is attenuated by stimulation, it is said to have been
"blocked" or to show "blocking".
 Low/attenuated: 10-20uV
 Suppressed <10uV

Cont.
132
2. Hypersynchrony: Seen as an increase in voltage & regularity of rhythmic activity,
or within the alpha, beta, or theta range.
 The term implies an increase in the number of neural elements contributing to the
rhythm.
(Note: term is used in interpretative sense but as a descriptor of change in the EEG).
3. Paroxysmal: Activity that emerges from background with a rapid onset, reaching
(usually) quite high voltage & ending with an abrupt return to lower voltage activity.
 Though the term does not directly imply abnormality, much abnormal activity is
paroxysmal.

EEG Artifacts
133
 Artifacts are recorded signals that are non cerebral in origin
(i.e. not coming from the brain).
 There are two types:
1. Physiologic artifacts: created by Physiological Process
2. Non - Physiologic artifacts: created by devices external to
the body.

Cont.
134
 Biological artifacts
 Eye artifacts (including eyeball, ocular muscles & eyelid)
 ECG artifacts
 EMG artifacts
 Glossokinetic artifacts
 Sweating
 Any minor body movement
 External artifacts
 50/60Hz
 Cable movement
 Broken wire contacts
 Low battery
 Too much electrode paste/jelly
 Poor grounding of the EEG electrodes
 the presence of an IV drip

Cont.
135

Cont.
136

Cont.
137

ECG Artifacts
Cont.
138

Procedure of EEG Recordings
139
 Required Instruments
 EEG machine (8/16 channels).
 Electrodes & Rubber cap.
 Electrode jelly & Syringe filled with conductive Jell.
 Alcohol swap
 Skin pencil & measuring tape.
 Cleaning Towel
 Quiet dark comfortable room.

Cont.
140

14
1
• Hyperventilation - causes cortical hypocapnia-> cerebral
vasoconstriction and hypoxia -> may allow epileptic foci to
become evident
• Photic stimulation - a strobe light flashing at 8-15 Hz is used to
capture the occipital α frequency - α frequency adjusts to match that
of the strobe - may allow epileptic foci to be seen and may even
induce epileptic seizures, as may a flickering television screen
• Sleep deprivation.
• Sleep EEG
Activation

Cont.
142
 Preparation for EEG in Hospital:
 Before coming to the test, Notify the client the following:
A. The patient will be asked to sign a consent form that gives him/her
permission to do the procedure.
B. The patient must wash his/her hair with shampoo, but conditioner
must not be used the night before the test.
C. The patient must Tell his/her healthcare provider of all medicines
(prescription & over-the counter) & herbal supplements that they
are taking.

Cont.
143
D. The patient must Discontinue using medicines that may interfere
with the test if the healthcare provider has directed him/her to do so.
E. The patient must Avoid consuming any food or drinks containing
caffeine for 8 to 12 hours before the test.
F. If the patient is having a sleep EEG, he or she may be asked to stay
awake the night before the exam.
G. The patient must Avoid fasting the night before or the day of the
procedure. Low blood sugar may influence the results.

Cont.
144
 During the EEG procedure:
A. A standard noninvasive EEG takes about 1 hour.
B. The patient will be positioned on a padded bed or table.
C. To measure the electrical activity in various parts of the brain, an
EEG technologist will attach electrodes to the scalp.

Cont.
145
D. To improve the conduction of these impulses to the electrodes, a
gel will be applied to them.
E. The technician may tell the patient to breathe slowly or quickly &
may use visual stimuli such as flashing lights to see what
happens in the brain when the patient sees these things.
F. The brain's electrical activity is recorded continuously
throughout the exam on special EEG Computer Monitor or paper.

Cont.
146
 After EEG procedure:
A. After the test is complete, the technician will remove the electrodes.
B. The patient will be instructed when to resume any medications.
C. The patient generally will be ready to go home immediately following
the test. No recovery time is required.

Cont.
147
D. The patient should avoid activities that may harm them if a
seizure occurs, until they have resumed their seizure medication
for an adequate length of time.
E. These precautions do not necessarily apply to the person who
was not on any seizure medication prior to the EEG.
F. The doctor or technician will tell the patient when & how they
will learn the results of their EEG

Cont.
148
 EEG results:
 When the EEG is finished, the results are interpreted by a neurologist.
 When examining the recordings, the neurologist looks for certain patterns
that represent problems in a particular area of the brain. (e.g., certain types
of seizures have specific brain wave patterns that the trained neurologist
recognizes.
 The neurologist look at all recorded tracings, decide what is normal & what is
not, & determine what the abnormal tracings represent.
 The neurologist forwards the EEG results to the doctor who ordered the test,
& the patient is then notified as arranged.

EEG Interpretation
149

Cont.
150

COMPREHENSIVE APPROACH TO EEG INTERPRETATION
151

Cont.
152

Cont.
153

Cont.
154

Cont.
155

Cont.
156

Normal EEG Waves
Habtemariam M.
157
 The billions of neurons in the human brain have highly
complex firing patterns, mixing in a rather complicated
fashion.
 The neural oscillations that can be measured with EEG are
even visible in raw, unprocessed data.
 However, the signal is always a mixture of several underlying
base frequencies, which are considered to reflect certain
cognitive, affective or attentional states.
11/25/2020

Cont.
Habtemariam M.
158
 Because these frequencies vary slightly dependent on
individual factors, stimulus properties & internal states,
research classifies these frequencies based on specific
frequency ranges, or frequency bands:
 Delta(δ) band (0 – <4 Hz)
 Theta(θ) band (4 – <8 Hz)
 Alpha(α) band (8 – 13 Hz)
 Beta(β) band (>13 – 25 Hz)
 Gamma(γ) band (> 25 Hz)
11/25/2020

Delta Waves (δ)
Habtemariam M.
159
11/25/2020
 Slowest & highest amplitude brainwaves.
 They are found most often in infants as well as young children.
 Frequency range: 0 Hz to <4 Hz
 Normal in adults who are in deep sleep & in young children.
 Usually only present during deep non-REM sleep (stage 3),
also known as slow wave sleep (SWS).

Cont.
160
 As we age, we tend to produce less delta even during deep
sleep
 Delta band power is examined to assess the depth of sleep.
 The stronger the delta rhythm, the deeper the sleep.
 Stronger in the right brain hemisphere, & the sources of
delta are typically localized in the thalamus.

Cont.
161
 Optimal: natural healing, restorative /deep sleep
 Increase delta waves: Depressants
 Too much: Brain injuries, learning problems, inability to
think
 Too little: Inability to rejuvenate body, inability to
revitalize the brain, poor sleep
 Location: frontally in adults, posteriorly in children

Not present in normal
awake EEG
Prominent in normal
deeper stage of sleep.
A frequency of < 4 Hz.
16
2
Cont.

Theta Wave (θ)
163
 It is normal for all ages during sleep.
 They generally aren’t obvious when adults are awake.
 Its range is involved in daydreaming & sleep.
 frontal theta activity correlate with the difficulty of
mental operations E.g. learning or during memory recall
 Frequency range: 4 Hz to <8 Hz

Cont.
Habtemariam M.
164
 Theta can be recorded from all over cortex.
 Optimal: Creativity, emotional connection, intuition,
relaxation
 Increase theta waves: Depressants
 Too much: depression, hyperactivity, impulsivity,
inattentiveness
 Too little: Anxiety, poor emotional awareness, stress
11/25/2020

Small amount of
sporadic and isolated
activity found in normal
awake state
Prominent in drowsy
and sleep EEG tracing
EEG activity of 4 to 7
HZ
found in frontal and
temporal region
16
5
Cont.

Alpha(α) Waves
Habtemariam M.
166
 It reflects sensory, motor & memory functions.
 Increased levels of alpha seen during mental & physical
relaxation with eyes closed.
 Alpha power is reduced during mental or bodily activity
with eyes open.
 E.g. during focused attention towards any type of stimulus
11/25/2020

Cont.
167
 Alpha suppression also indicates brain is
 pick up information from various senses,
 coordinating attentional resources &
 focusing on what really matters in that particular
moment.
 Frequency range: 8 Hz to 13 Hz

Cont.
168
 Too much: Daydreaming, inability to focus, too relaxed
 Too little: Anxiety, high stress, insomnia
 Increase alpha waves: Alcohol, marijuana
 Optimal: Relaxation
 Location: posterior regions of head, both sides, higher in
amplitude on dominant side

Cont.
169

ALPHA BLOCK
170
 When the subject's eyes are closed, the alpha rhythm is
generated.
 As soon as the eyes are open, alpha disappears & is
replaced with the beta rhythm.
 This is called alpha block & may be elicited also by
mental activity.

Cont.
171

Beta(β) Waves
172
 These are known as high frequency low amplitude brain
waves that are commonly observed while awake.
 They are involved in conscious thought, logical thinking, &
tend to have a stimulating affect.
 Frequency range: >13 Hz to 25 Hz
 Too much: Adrenaline, anxiety, high arousal, inability to relax,
stress
 Too little: daydreaming, depression, poor cognition

Cont.
173
 Optimal: Conscious focus, memory, problem solving
 Increase beta waves: Coffee, energy drinks, various
stimulants
 Location: on both sides in symmetrical distribution & is
most evident frontally but also posteriorly

Cont.
174
 Active, busy or anxious thinking & active concentration
are generally known to correlate with higher beta power.
 Over central cortex (along the motor strip), beta power
becomes stronger as we plan or execute movements,

Frequent in normal
eye open EEG
EEG waves of >13 HZ
Usually of low voltage
Found in frontal and
central region
17
5
Cont.

Gamma(γ)Waves
176
 It is still exactly unclear where in the brain it generated
& what these oscillations reflect.
 Some researchers argue that it involves in higher
processing tasks as well as cognitive functioning.
 Frequency range: > 25 Hz
 Optimal: Binding senses, cognition, information
processing, learning, perception, REM sleep

Cont.
177
 Increase gamma waves:
Meditation
 Too much: Anxiety, high
arousal, stress
 Too little: depression, learning
disabilities
 Location : Somatosensory
cortex (lateral parietal lobe of
the human brain)

1- Slowing
179
Normal slow activities:
1- theta during drowsiness
2- delta during sleep.
• focal delta during the waking state or
• theta for a posterior dominant rhythm in the waking state is
clearly abnormal.

Slowing can be divided into three classifications:
180
1 Generalized slowing:
 >> Encephalopathic slowing : slowing of the posterior dominant rhythm,
disorganization of the rhythm, & excessive theta activity anteriorly.
2 Regional slowing:
 >> seen in encephalopathy
 >> affect one portion of the brain yet not be focal to a single area.
 >> E.g. frontal intermittent rhythmic delta (FIRDA) or slowing of the
posterior dominant rhythm (background will be normal)
3 Focal slowing:indicative of a structural lesion, &
 includes focal theta activity & polymorphic delta activity

2- Spike & sharp waves
Durations:
>> spike 20-70 ms
>> Sharp waves 70-200 ms.
>> Potentials of less than 20 ms duration muscle fibers or electrical
artifact.
185

MORPHOLOGY OF SPIKES
186

• Vertex waves
• Occipital lambda waves
• POSTS – positive occipital sharp transients of sleep
• Wicket spikes
• BETS – benign epileptiform transients of sleep (sss)
• 6-per-second (phantom) spike & wave
• 14- & 6-Hz positive spikes
Normal spike-like potentials
189
https://emedicine.medscape.com/article/1139332-overview#showall

Sleep spindle/Vertex sharp wave
190

Lambda/POSTS
191

Drowsiness/ drop out alpha & POSTS
Sleep Awake
192

Benign epileptic transients of sleep
193

Wicket (Mu waves)
194

Cont.
195

•Focal slowing – usually suggests a focal structural lesion
underlying the scalp electrodes.
•Focal spikes or sharp waves - can correlate with a focal structural
lesion but more commonly suggests a partial seizure disorder.
• Diffuse slowing – usually associated with encephalopathy
• Diffuse spikes or sharp waves – correlate with a generalized
seizure disorder.
Focal vs generalized abnormalities
197

Abnormal frequency composition
1. Excessive fast activity is usually seen in patients sedated with
benzodiazepines – beta activity is prominent frontally.
2. Excessive theta activity : Theta is not a prominent component
of the background in waking adults, & when it stands out from the
baseline is abnormal
3. Slow activity
198

Slow activity
199
A- Diffuse slowing
1- Slowing of the posterior dominant rhythm
>> Slowing of the PDR to less than 8.5 Hz is always abnormal in adults.
>> The slow posterior dominant rhythm differs from the normal faster rhythm in a few
ways:
 Slow PDR is less stereotyped than normal PDR, with bumps on the waves
 Slow PDR is less reactive to eye opening than normal PDR, it does not show
the degree of attenuation of normal PDR
 Slow PDR is often associated with theta prominent more forward of the
occipital regions than the normal PDR extending forward of the occipital regions.

>> The slow PDR is interpreted as being abnormal, but is not
specific. Possible causes include:
• Toxic-metabolic encephalopathy
• Degenerative dementia
• Multifocal vascular disease
>> Subharmonic PDR (Normal variant): may appear to be a 5-
6 Hz PDR with otherwise normal frequency composition &
appearance of the EEG.
Cont.
200

Cont.
201
>> The subharmonic PDR can be differentiated from slowing of the
PDR in the following ways:
 Slowing of the PDR in the 5-6 Hz range should be
associated with slowing seen anteriorally to the occipital
lobes, whereas subharmonic PDR has otherwise normal
frequency compositions.

Cont.
202
 Slowing of the PDR in the 5-6 Hz range will usually not
attenuate completely to eye opening, whereas
subharmonic PDR completely attenuates.
 Slowing of the PDR in the 5-6 Hz range with have an
irregular, polymorphic appearance, whereas
subharmonic PDR is regular, & usually notched, so that
the underlying 10 Hz rhythm can be seen.

Normal PDR
203

2- Slow activity superimposed on the waking background
>> Theta & delta activity in waking records is usually abnormal.
>> Diffuse slowing is usually polymorphic delta or irregular theta which is
seen from both hemispheres.
>> Causes :
• Encephalopathy due to toxic or metabolic causes
• Cerebrovascular disease which is multifocal or diffuse
• Head injury
Cont.
204

Cont.
205
3- Generalized slowing in sleep recordings
• abnormal slowing in a sleeping record is much more difficult.
• The sleep record consists of slow activity in the theta & delta range, & the
exact pattern depends on sleep stage.
• encephalopathy should be the interpretation of a sleep record only if the
slow activity is inconsistent with any stage of the sleep-wave cycle.
• Conversely, normal sleeping record does not rule-out an encephalopathy.

B- Focal slowing & polymorphic delta activity
>> Focal slowing usually indicates a focal structural lesion of the hemispheres.
>> polymorphic delta activity(PDA): Focal slowing is irregular &
composed of delta activity with theta activity superimposed.
• PDA often appears on a disorganized EEG background, but the background
may actually be normal
Cont.
206

Cont.
207
• PDA is the most common finding in focal structural lesions
such as tumors, contusion, hemorrhage, infarction, &
abscess.
• The presence of focal spikes or sharp waves without another
disturbance on the background is seldom a sign of a focal
parenchymal lesion.
• Focal slowing is nonspecific
• Complicated migraine & postictal state may cause focal slowing.

C- Intermittent rhythmic delta activity
>> always a sign of cerebral dysfunction
>> Slow activity is seen at about 2.5 Hz
>> In adults, the rhythmic slow activity is usually frontal, hence
frontal intermittent rhythmic delta activity(FIRDA).
>> In children, the slowing is commonly seen in the occipital
regions, hence the term occipital intermittent rhythmic delta
activity (OIRDA)
Cont.
209

Cont.
210
>> The rhythmic slowing of FIRDA & PIRDA may last for
several seconds then disappear for longer intervals, hence the
intermittent nature of the rhythm.
>> The slow activity is augmented by eye closure or
hyperventilation, but attenuated by stimulation or by non REM
sleep.
>> FIRDA reappears in REM sleep.

Cont.
211
>> PIRDA is seen occasionally in children with absence epilepsy.
>> Both FIRDA & PIRDA can be caused by:
• midline tumors
• metabolic encephalopathy
• degenerative disorders
• some encephalitides
>> FIRDA is differentiated from PDA by the latter’s lack of reactivity to the
stimulus, usual unilateral appearance, lack of rhythmicity, & the continuous
appearance

D- Slow activity as a seizure discharge
>> Seizures occasionally manifest on routine EEG as rhythmic slow waves.
>> the spike component is very small in amplitude .
>> Epileptiform slow activity interferes with the normal background, whereas
FIRDA may be associated with an otherwise near-normal background.
>> Epileptiform slow activity is differentiated from PDA by the stereotypic
nature of the epileptiform activity.
>> Epileptiform waves tend to be smoother, & if the discharges are
bilateral, there is usually a high degree of interhemispheric synchrony.
Cont.
213

Cont.
214
E- Focal loss of EEG patterns
>> Focal attenuation of EEG activity usually indicates a structural
lesion.
>> Beta activity is most sensitive to this effect.
>> Occipital lesions can cause unilateral loss of the posterior alpha.
>> Unilateral lesions may also disrupt sleep patterns so that sleep
spindles, vertex waves, or both are not seen from the affected
hemisphere.
>> Unilateral suppression is commonly seen with subdural hematoma.

Spikes & sharp waves
A- Focal sharp activity
• indicate a seizure disorder of with partial onset, a structural lesion in the
absence of seizure activity.
• Frontocentral discharges may be seen in patients with simple partial
seizures.
• Temporal or frontal spikes may be seen in patients with complex partial
seizures.
215

Cont.
216
• Normal focal spike-wave complexes include:
>> 14- & 6-Hz positive spikes
>> subclinical rhythmic electrographic discharge of adults (SREDA)
>> wicket spikes.
• A single spike during the course of a recording should not be
interpreted as abnormal,

B- Focal spikes associated with seizures
>> Focal spikes are associate with partial seizures & the benign epilepsies of
childhood.
>> Partial seizures are divided into simpleand complex, based on symptomatology
rather than EEG findings.
>> The benign epilepsies of childhood can manifest as focal & generalized
seizures.
Cont.
217

Cont.
218

• shows prominent spiking over the involved cortex,
• A typical pattern might be left central spikes in a patient who presents
with focal seizures affecting the right arm.
• The epileptiform activity may occur in deep layers of cortex &
subcortical structures so that the spike potentials are not projected to
the surface electrodes.
Simple partial seizure
219

Cont.
220
• Partial seizures may spread throughout the
hemispheres, resulting in a secondary generalization
• Secondary generalized seizures may have a focal onset
which can be detected clinically , but this is not always
the case.

Cont.
221

• shows focal spikes in the temporal or frontal region.
• Routine EEG may not detect the spikes if they originate in
cortex that is not directly underlying the surface electrodes.
Complex partial seizures
• may have secondary generalization.
• EEGshowing focal activity prior to the generalization.
Complex partial seizure
222

Cont.
223

• they are age-related & seldom persist into adult life.
• There are two types: rolandic & occipital.
1- Rolandic epilepsy
>> interictal discharges arising from the central regions, localized near
electrodes C3 & C4.
>> The interictal discharges are independent & augmented by sleep.
Benign focal epilepsies of childhood
224

Cont.
225
>> Relatives of patients with rolandic epilepsy may have EEG
abnormality as a genetic marker without clinical seizures.
>> The discharges of rolandic epilepsy are so characteristic in location &
pattern that they are seldom confused with other pathologic activity.
>> Independent central spikes are seen on an otherwise normal
background. This must be differentiated from multifocal spikes, however.

2- Occipital epilepsy
>> interictal sharp waves with predominance at O1 & O2.
>> Rolandic & occipital epilepsy may occur in the same families
>> During the seizure, the EEG shows 2-3/sec spike- wave discharges
with predominance in the occipital region.
>> The interictal discharge may be blocked by photic stimulation or eye
opening.
Cont.
227

Cont.
228

4- Focal sharp activity without seizures
>> occasionally seen in patients with no clinical seizures.
>> About 3% of normal individuals exhibit epileptiform activity on
EEG.
>> Approximately 25% of these discharges are focal.
>> Some of these patients will go on to develop seizures
Cont.
229

Cont.
230
>> these patients should not be treated with anticonvulsants without
clinical evidence of convulsive activity.
>> Subclinical rhythmic electrographic discharge of adults (SREDA)
is sharply contoured rhythmic delta activity with prominent in the
centroparietal region. This pattern is seen in older patients & has no
definite clinical correlate.
>> Some patients with congenital blindness may exhibit occipital
spikes. These should not be interpreted as epileptiform.

Generalized sharp activity
231

1) 3-per-second spike-wave
>> is usually equated with absence epilepsy.
>> may exhibit other seizure types, including generalized tonic-clonic
seizures.
>> The 3-per-second spike-wave complex is synchronous from the
two hemispheres, with highest amplitude over the midline frontal
region.
Cont.
232

Cont.
233
>> The lowest amplitudes are in the temporal & occipital regions.
>> The frequency changes slightly during the course of the discharge,
beginning close to 4/sec & declining to 2.5/sec.
>> Immediately following the discharge, the record quickly returns to
normal.
>> The spike component may have a double spike or polyspike
appearance.

>> If absence epilepsy is considered, the patient should be asked to
hyperventilate for 5 minutes instead of the usual 3 minutes.
>> Children with absence seizures become symptomatic if the discharge lasts
longer than 5 seconds.
>> During the discharge, the technician should ask the patient a question.
>> The patient with absence seizures often answers after the discharge. The
question & the response should be noted on the record.
Cont.
234

Cont.
235
>> The 3-per-second discharge is less well organized during
sleep than during the waking state.
>> Its appearance is more polyspike in configuration & the
spike-wave interval is less regular.
>> The spike component is polyspike in some patients.
Patients with this polyspike pattern are more likely to
exhibit myoclonus.

• The 3-per-second spike-wave pattern correlates well with primary generalized epilepsy, if the
remainder of the recording is normal.
• Factors which would make the clinical doubt the diagnosis of primary generalized epilepsy include:
>> abnormal EEG background
>> focal discharges
>> history of slow neurologic development
>> abnormal neurologic examination
• Treatment of absence epilepsy often abolishes the interictal discharge. This is different from
most focal epilepsies in which interictal spiking persists despite good seizure control.
Cont.
237

2- Slow spike-wave complex
• 2.5/sec or less.
• The morphology is less-stereotyped than the 3-per-second spike-wave
complex.
• The duration of the slow spike is usually more than 70 ms, which is
technically a sharp wave.
Cont.
238

Cont.
239
• The complex is generalized & synchronous across both
hemispheres, with the highest amplitude in the midline
frontal region.
• During sleep, the slow spike-wave complex may be
continuous.
• This activity may not indicate status epilepticus but rather
represents activation of the interictal activity with sleep.
• frequently associated with the Lennox-Gastaut syndrome.

• In the Lennox-Gastaut syndrome, the slow spike-wave
complex is usually an interictal pattern, but may also be ictal.
• Since these patients have a mixed seizure disorder, ictal events
may show patterns other than the slow spike-wave complex,.
• Atonic seizures are characterized by generalized spikes during the
myoclonus followed by the slow spike-wave pattern during the
atonic phase.
Cont.
240

Cont.
241
 Atonic seizures are most characteristic of the Lennox-Gastaut
syndrome.
 Akinetic seizures are characterized by the slow spikewave
discharge throughout the seizure.
 Tonic seizures occur in Lennox-Gastaut syndrome & are
characterized by a rapid spike activity or desynchronization
rather than the slow spike-wave complex.

Cont.
242

4- Fast spike-wave complex
• The fast spike-wave complex has a frequency of 4-5/sec &
has the appearance of slow waves with superimposed sharp
activity, rather than distinct spike-wave complexes.
• Maximal amplitude is in the fronto-central region.
Cont.
243

Cont.
244
 Patients have generalized tonic-clonic seizures with or
without myoclonus.
 Absence seizures are rare.
 seen in patients with idiopathic generalized tonic-clonic
seizures.
 The discharge is not as stereotyped as the 3-per-second
spikewave complex, & the synchrony is less prominent.

4) 6-per second (Phantom) spike-wave complex
• characterized by brief trains of small spikewave complexes which
are distributed diffusely over both hemispheres, with a frontal or
occipital predominance.
• They are most common during the waking & drowsy states
& disappear during sleep.
Cont.
245

Cont.
246
 Frontal predominance is frequently associated with
generalized tonic - clonic seizures, whereas occipital
predominance is not associated with clinical seizures.
 Hughes (1980) provided the acronyms WHAM & FOLD.
 WHAM = waking record, high amplitude, anterior, males.
 FOLD = females, occipital, low amplitude, drowsy.
 WHAM is associated with seizures & FOLD is not.

5) Hypsarrhythmia
• high-voltage bursts of theta & delta waves with multifocal sharp
waves superimposed.
• The bursts are separated by periods of relative suppression.
• flattening of the EEG may be an ictal sign, indicating that there has been
sudden desynchronization of the record.
Cont.
248

6) Periodic patterns
• Periodic discharges usually indicate cortical damage, & can be due to
stroke, anoxia, infection, degenerative disorders, & other conditions.
• The periodic patterns can be focal, regional, or generalized, with
regional distribution being them most common
Cont.
250

Cont.
251
A) Periodic lateralized epileptiform (PLEDs)
• Discharges are high-amplitude sharp waves that recur at a rate of 0.5-
3.0/sec.
• They are prominent over one hemisphere or one region.
• When bilateral, they are independent, thereby keeping the term
lateralized.
• PLEDs are a sign of parenchymal destruction & most commonly seen in
strokes.

Cont.
252
 Other important causes include head injury, abscess, encephalitis,
hypoxic encephalopathy, brain tumors, & other focal cerebral
lesions. It is impossible to distinguish definitively between causes
on the basis of waveform.
 Of the encephalitides, herpes simplex most commonly produces
PLEDs.
 Other viral infections produce slowing without PLEDs

• The PLEDs have an amplitude of 100-300 µV.
• An early negative component is followed by a positive wave.
• The discharge may be complex, with additional sharp & slow components
superimposed on the waveform.
• Patients with PLEDs may have myoclonic jerks that are either synchronous with the
jerks or independent.
• When the jerks are independent, the generator for the myoclonus is probably deep.
• Even when they are synchronous, the generator is probably subcortical.
• The cortical discharge reflects projections from the deep generator.
Cont.
253

B) Herpes simplex encephalitis
• usually shows PLEDs on EEG during some phase of the illness ,
although at other times, there is slowing in the theta & subsequently
delta range.
• The PLEDs are sharply contoured slow waves with a frequency of 2-
4 Hz.
• The duration of each wave is often more than 50 msec.
Cont.
255

Cont.
256
• This relatively slow frequency of repetition helps to
differentiate PLEDs in herpes encephalitis from the higher
frequency discharges of SSPE.
• Neonates with herpes encephalitis may have necrosis that is
not confined or even most prominent in the temporal region.
These patients often do not have PLEDs.
• The EEG may show a poorly organized background with
slow activity in the delta range predominating.

C) Anoxic encephalopathy
• The background is disorganized with diffuse slowing & suppression.
• Periodic sharp waves are often seen & may predominate in the record.
• They look similar to PLEDs, except that they are synchronous between
the hemispheres.
• Patients may have myoclonus associated with the discharges.
• These probably represent the extreme of the burst suppression pattern, seen
often in patients with anoxic encephalopathy.
Cont.
259

Cont.
260
D) Burst-suppression pattern
• occurs in patients with severe encephalopathies.
• often seen in patients with hypoxic ischemic damage & in barbiturate coma.

E) Subacute sclerosing panencephalitis
• Periodic complexes are seen in most patients at an intermediate stage.
• Early on, there may be only mild slowing, with disorganization of the
background.
• Late in the course, the periodic complexes may completely disappear,
leaving the recording virtually isoelectric.
• The discharges are slow waves with sharp components.
Cont.
262

Cont.
263
 The duration of the complex is up to 3-sec, & the interval
between complexes is 5-15 sec.
 The background during the interval is disorganized &
generally suppressed.
 Myoclonus is typically synchronous with the discharge.
 EEG in SSPE resembles the burst-suppression pattern.
 The background is usually more suppressed with burst
suppression than SSPE.

F) Creutzfeldt-Jakob disease
• EEG findings which depend on stage of the disease.
• At some point in the disease process, a periodic pattern is seen, composed of
a sharp wave or sharply-contoured slow wave.
• The interval between discharges is 500-2,000 ms.
• The discharges are maximal in the anterior regions & may occasionally
be unilateral.
• Only laterally are the discharges prominent posteriorally & when so
are commonly associated with blindness.
Cont.
265

Cont.
266
 The discharges may or may not be temporally locked to myoclonus.
 These discharges are superimposed on an abnormal background
haracterized by low-voltage slowing in the theta & delta range.
 The periodic complexes abate in sleep.
 Early in the course, the periodic complexes cannot be seen & the
only finding may be focal or generalized slowing.
 About 10-15% of patients may not show periodic patterns during
their course

Summary
Habtemariam M.
268
 EEG is the record of electrical activity of brain (superficial layer
i.e. the dendrites of pyramidal cells) by placing the electrodes on
the scalp.
 Created by Hans Burgers
 Normal Types of Waves: Delta, Theta, Alpha, Betha, Gamma
11/25/2020

Proposed Research Titles
269
1. Hypoglycemia-induced decrease of EEG coherence in patients
with type 1 diabetes at Dessie referral hospital 2020
2. Continuous EEG findings in patients with covid‐19 infection
admitted to Boru Meda hospital 2020
3. EEG monitoring duration to identify electroencephalographic
seizures in critically ill adult patients of Dessie referral hospital
2020
4. Evaluation of stroke using EEG frequency analysis & topographic
mapping among adult patients of Dessie referral hospital 2020

References
270
1. Bigos, K.L.; Hariri, A.; Weinberger, D. (2015). Neuroimaging Genetics: Principles and Practices. Oxford University Press. p. 157. ISBN 978-0199920228.
2. Davey, G. (2011). Applied Psychology. John Wiley & Sons. p. 153. ISBN 978-1444331219.
3. Davies, Melissa (2002-04-09). "The Neuron: size comparison". Neuroscience: A journey through the brain. Retrieved 2009-06-20.
4. Gray's Anatomy 2008, p. 227-9.
5. Guyton & Hall 2011, pp. 698–9.
6. Haines, D; Mihailoff, G (2018). Fundamental neuroscience for basic and clinical applications (Fifth ed.). p. 152. ISBN 9780323396325.
7. Luck (2014, 2nd edition). An introduction to the event-related potential technique. Cambridge, MA: MIT Press.
8. Medline Plus Medical Encyclopedia
9. Niedermeyer E.; da Silva F.L. (2004). Electroencephalography: Basic Principles, Clinical Applications, and Related Fields. Lippincott Williams & Wilkins. ISBN 978-0-7817-5126-1.
10. Nowakowski RS (August 2006). "Stable neuron numbers from cradle to grave". Proceedings of the National Academy of Sciences of the United States of America. 103 (33): 12219–20.
Bibcode:2006PNAS..10312219N. doi:10.1073/pnas.0605605103. PMC 1567859. PMID 16894140
11. Smith; Kosslyn (2007). Cognitive Psychology: Mind and Brain. New Jersey: Prentice Hall. pp. 21, 194–199, 349.
12. SparkNotes: Brain Anatomy: Parietal and Occipital Lobes". Archived from the original on 31 December 2007. Retrieved 27 February 2008.
13. Yang X, Gao M, Shi J, Ye H, Chen S (2017). "Modulating the Activity of the DLPFC and OFC Has Distinct Effects on Risk and Ambiguity Decision-Making: A tDCS Study". Frontiers in
Psychology. 8: 1417. doi:10.3389/fpsyg.2017.01417. PMC 5572270. PMID 28878714
14. Zhao B, Meka DP, Scharrenberg R, König T, Schwanke B, Kobler O, Windhorst S, Kreutz MR, Mikhaylova M, Calderon de Anda F (August 2017). "Microtubules Modulate F-actin Dynamics
during Neuronal Polarization". Scientific Reports. 7 (1): 9583. Bibcode:2017NatSR...7.9583Z. doi:10.1038/s41598-017-09832-8. PMC 5575062. PMID 28851982
15. Costanzo, Linda S. Physiology (2018) 6th edition, pp. 18-21
16. Luck (2014, 2nd edition). An introduction to the event-related potential technique. Cambridge, MA: MIT Press.
17. Buzsáki, Anastassiou, & Koch (2012). The origin of extracellular fields and currents – EEG, ECoG, LFP and spikes. Nature Reviews Neuroscience, 13(6), 407–20.
18. Kondylis, Efstathios D. (2014). "Detection Of High-Frequency Oscillations By Hybrid Depth Electrodes In Standard Clinical Intracranial EEG Recordings". Frontiers in Neurology. 5: 149.
doi:10.3389/fneur.2014.00149. PMC 4123606. PMID 25147541.
19. Haas, L F (2003). "Hans Berger (1873-1941), Richard Caton (1842-1926), and electroencephalography". Journal of Neurology, Neurosurgery & Psychiatry. 74 (1): 9. doi:10.1136/jnnp.74.1.9.
PMC 1738204. PMID 12486257.
20. Millet, David (2002). "The Origins of EEG". International Society for the History of the Neurosciences (ISHN).

Acknowledgment
Habtemariam M.
271
 First I would like to express my heartfelt gratitude to WU
CMHS for giving me this chance to enhance my knowledge &
skill.
 Secondly I would like to thank my instructor Dr. Prem Kumar
for sharing me his deep knowledge, experience & expertise.
 Last but not least I would like to thank my family & friends in
helping me in ideas & material during my entire work.
11/25/2020

Thank You
Habtemariam M.
272
11/25/2020

Electroencephalography (EEG): an electrophysiological monitoring method to record electrical activity of the brain.

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