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Electroencephalogram

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EEG

Electro-encephalogram: Representation

of the bio-potentials generated by the

brain.

Electro-encephalography:

Instruments to record these bio-

potentials.

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How it started:

The Invention of the EEG

In 1929, the German psychiatrist Hans Berger announced

something unexpected and revolutionary: the human brain is

continuously electrically active. This was the beginning of

the EEG, which was a method Berger invented to

graphically record this electrical activity on paper.

An early EEG by Berger, circa

1928

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The Beginnings of Clinical

Neuropsychology

At the time this was considered cutting edge, with Bergers

discoveries spawning the field of clinical neuropsychology.

http://images.google.com/imgres?imgurl=www.csbsju.edu/psychology/images/instruments-eeg.jpg&imgrefurl=http://www.csbsju.edu/psychology/resources/default.htm&h=512&w=640&sz=32&tbnid=i62CrsYNbsUJ:&tbnh=108&tbnw=135&start=23&prev=/images%3Fq%3DEEG%26start%3D20%26hl%3Den%26lr%3D%26ie%3DUTF-8%26sa%3DN

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EEG-Definition

The electroencephalogram (EEG) is a measure of brainwaves.

It is a readily available test that provides evidence ofhow the brain functions over time.

The electroencephalogram (EEG) is a medical test usedto measure the electrical activity of the brain.

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EEG records brain waves

It doesn't read minds or measure IQs.

Instead, it's used to detect the level ofelectrical activity in the brain.

Your brain cells communicate by electricalimpulses, and an EEG measures and records

these electrical impulses to detect anythingabnormal.

Definition-..ctd

http://kidshealth.org/parent/general/body_basics/brain_nervous_system.htmlhttp://kidshealth.org/parent/general/body_basics/brain_nervous_system.html

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EEG - USE Stupor

Reduced or slowed responsiveness

Coma: Unresponsiveness

Head injuries

Brain infection

Brain haemorrhage

Degeneration of brain tissue

Metabolic conditions that affect brain tissue

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EEG - USE

Confusion

Tumors

Long-term difficulties with thinking or

memoryWeakening of specific parts of the body

To determine brain death

Sleep disorders

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EEG ACTIVITY

The rhythmic activity of the brain isdesignated by its frequency

EEG activity can be broken down into 4

distinct frequency bands:

Beta activity > 13 Hz

Alpha activity 8 Hz-13 Hz

Theta activity 4 Hz-7 Hz

Delta activity < 4 Hz

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Beta activity is a normal activity present when

the eyes are open or closed.It tends to be seen in the channels recordedfrom the centre or front of the head.

Some drugs will increase the amount of betaactivity in the EEG.

Associated with active, busy or anxious thinkingand active concentration.

BETA ACTIVITY

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ALPHA ACTIVITY

Alpha activity is also a normal activity

It is only seen when the eyes are closed andshould disappear or reduce in amplitude when the

eyes are open.

It is characteristic of a relaxed, alert state of

consciousness

Alpha rhythms are best detected with the eyes

closed

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THETA ACTIVITY

Normal and abnormal activity depending on the

age and state of the patient.

It is associated with drowsiness, childhood,

adolescence and young adulthood

In adults it is normal if the patient is drowsy.

However it can also indicate brain dysfunction

if it is seen in a patient who is alert and awake.

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DELTA ACTIVITY

Delta activity is only normal in an adult patient

if they are in a moderate to deep sleep.

It is seen in deep sleep.

If it is seen at any other time it would indicate

brain dysfunction.

Abnormal activity may be seen in all or some

channels depending on the underlying brain

problem.

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EVOKED POTENTIALS

DEFINITION: The electrical response of the brain to a

specific stimulus(e.g. photic & sonic).The patient is exposed to the above mentioned stimuli for

detecting the results of these stimuli. These potentials are

averaged out from normal EEG activity.

PHOTIC STIMULUS:Given in manual or automatic mode.

The stimulator output can be fed to the markerchannel.

Frequency of the photic stimulus range-1Hz to 30 Hz.SONIC STIMULUS:Given in manual mode.Frequency of sonic stimulus is adjustable up to 10 kHz.

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EEG Measurements

An EEG is performed by picking up signals from thescalp by using 23 active electrodes.

Amplitude: 10 microvolt to 100 microvolt.

Frequency: 1Hz to 100 Hz.

ELECTRODES:

Surface,Pad,Sub-dermal and silver ball.

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Electrodes

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EEG Measurements

An EEG is a recording of electrical signals from the

brain made by hooking up electrodes to the patient'sscalp.

These electrodes pick up electric signals naturally

produced by the brain and send them to galvanometers

(instruments that detect and measure small electriccurrents)

Galvanometers are in turn hooked up to pens, under

which graph paper moves continuously. The pens trace

the signals onto the graph paper.

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EEG- Measurements

Scalp electrodes are used to record the

electroencephalogram (EEG) using a machine called

an electroencephalograph.

This record is the result of the activity of thousands

of neurons in the brain.

The pattern of activity changes with the level of aperson's arousal

If a person is relaxed, then the EEG has many

slow waves

If a person is excited, then the EEG has many

fast waves.

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Electrode Placement

Standard: 10-20 electrode placement is used.

Devised by an committee of the International

Federation of Societies for Electroencephalography.

The "10" and "20" refer to the 10% or 20%

interelectrode distance.

The electrode spacing is based on intervals of 10 and

20 percent of the distance between specified points on

the scalp. .

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LOBES

Frontal- Front part of the brain which contains

primary motor neurons.

Pre-frontal: Forward part contains neurons for

specified motor control functions like eye movement.

Parietal: Somatic inputs e.g heat,smell,fingers,tongueand arms etc lead to this part.

Occipital- Very back of the head and is responsible for

mapping of the patterns obtained in retina in

geographic representation.

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Electrode Placement

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Electrode Placement

Each point on this figure to the left indicates a possible

electrode position.

Each site has a letter (to identify the lobe) and a number

or another letter to identify the hemisphere location.

The letters F, T, C, P, and O stand for Frontal, Temporal,

Central, Parietal and Occipital. (Note that there is no

"central lobe", but this is just used for identification

purposes.)

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.

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Electrode Placement

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EEG ARTIFACTS

The amplitude of noise should be the least w.r.t

biological signal.

SYMPTOMS:

Fuzziness or thickness of the trace,sudden large

changes in voltage or repetitive sharp sawtoothed

waveforms.CAUSES:-

EMI from power line etc.

Faulty electrode application.

Patient movement.Muscle artifacts.(from gritting teeth or restlessness.

Blinking of eyes.

G i

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EEG-Block Diagram

Balance

bridge type

differential stage

Diff

AMP

Pre

AMP

50 HZ

Filter

Lo Linear

&

HI Linear Filter

Power

Amp

Graphic

Display

Output

El d R di

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Electrode Recording

The recording is obtained by placing electrodes on

the scalp,

Application of a conductive gel to reduce

resistance.(To reduce interference and minimize the

effect of electrode movement.)

Each electrode is connected to an input of adifferential amplifier (one amplifier per pair of

electrodes), which amplifies the voltage between

them (typically 1,000100,000 times,

El d A lifi

http://en.wikipedia.org/wiki/Electrodehttp://en.wikipedia.org/wiki/Differential_amplifierhttp://en.wikipedia.org/wiki/Differential_amplifierhttp://en.wikipedia.org/wiki/Electrode

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Electrode-AmplifierEEG machines use a differential amplifier to produce each

channel or trace of activity.

Each amplifier has two inputs.An electrode is connected to each of the inputs.

Diff i l A lifi

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Differential Amplifier

Measure the voltage difference between the two

signals at each of its inputs.

The resulting signal is amplified and then

displayed as a channel of EEG activity.

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M t

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Montage

The manner in which pairs of electrodes

are connected to each amplifier of theEEG machine is called a montage.

Each montage will use one of thefollowing standard recording derivations,

Monopolar derivation

Bipolar derivation

M l R di

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Monopolar Recording

Common reference derivation

Each amplifier records the difference between ascalp electrode and a reference electrode.

The same reference electrode is used for allchannels.

Reference electrode placed somewhere along thescalp midline, or a reference that links both earlobeelectrodes.

Bi l R di

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Bipolar Recording

The electrodes are connected in series to an equal

number of amplifiers.Electrodes linked together usually in straight linesfrom the front to the back of the head or transverselyacross the head.

Example, amplifier 1 measures the difference betweenelectrodes A and B, amplifier 2 measures the differencebetween B and C, and so on.

EEG MACHINE

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EEG MACHINE

EEG MACHINE CONSISTS OF THREEPARTS:

Trolley,Console and chart drive.

Trolley: The machine is fitted on a trolley that

has four wheels, the transformer is also fitted

inside the lower part of the trolley.

Console:Console of the machine comprises ofchannel amplifier modules and the mastercontrol panel.

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AMPLIFIER CONTROLS

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AMPLIFIER CONTROLS

1. mV/uV switch- It selects the range of the bio-

potentials to be recorded.

2. Sensitivity- It sets the sensitivity of the incoming

signal per cm or per mm.It has 11 positions.

Standard setting is 7.5 mm

3. Equalizer- Used to set the gain

4. Lo-Linear filter- Used to cut-off lower frequency.

It has 4 positions Standard setting70 Hz.

5. 50 Hz filter- Used for removing AC interference.

6. Stand by- ON,STAND BY or OFF switch.

7. Base Line:Used for electrical centering.

MASTER CONTROLS

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MASTER CONTROLS

1. All channel sensitivity-

To increase or decrease the sensitivity of allchannels.

It has four positions.Std setting is 0.

2. All channel LO&HI filter- To limit frequency

response of all channels.3. Calibration-

1. Used to select CAL.voltage.

2. It has 11 positions. Standard setting is 50

micro volts4. CAL push button-For giving a CAL. Pulse.

5. CAL/USE: For selecting CAL or record mode.

MASTER CONTROLS ctd

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MASTER CONTROLSctd

6.All channel montage selector:For automatic

electrode selection.

7. Electrode Resistance test- For measuring electrode

impedance.

8. Individual electrode selectors- These selectors areused for customized recording and are two per

channel.

9. Input jacks- These are the test points used to

check the connectivity between the electrode box andthe amplifier inputs.

CHART DRIVE

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CHART DRIVE

The chart drive has permanent magnets

galvanometer(moving coil),DC motor with gear

assemble to run the paper.

Following consoles are provided on the chart

drive:1. Main Switch- It is used to switch ON or OFF the

power.

2. Speed Selector- It is used to select the chart speed.

It has four selections. The standard speed

30m/sec.

CHART DRIVE

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CHART DRIVE

3. Stop/Chart/Chart-pen:-

In STOP position the recording pens and thepaper pulling mechanism are stationary.

CHART position- paper moves without pen

deflection.CHART-Pen position the pen writes on the

moving paper.

4. Pen lifter- This is a rotary knob which lifts the

pens from the writing surface.

General Operating Procedure

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General Operating Procedure

1. Turn the machine ON and allow it to warm up for

15 minutes.

2. Load the machine with paper and fill the ink

wheels with ink.

3. Make sure that the base line of all pens is

centered.

4. Set all amplifier controls at standard setting.

CALIBRATION PROCEDURE

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CALIBRATION PROCEDURE

1. Turn the CAL/USE switch to CAL position and

select the cal signal to 50uV position.

2. Turn the Chart-pen switch to chart pen position

and depress the CAL push button each sec.

3. Adjust the height of the upward deflection of the

pen by using the sensitivity equalizer on each

amplifier(7mm).

Recording Procedure

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Recording Procedure

1. Apply electrodes according to the 10-20 system and

connect them to the corresponding jacks on the

electrode board and check the electrode impedance.

2. Turn the CAL/USE to USE position.

3. Perform the TEST run an switch the chart drive to

STOP position.

4. Turn the master montage selector to first (A) position

and run the machine upto 5 pages of recording.

5. Before selecting the second(B) montage switch thechart drive to STOP position.

6. Repeat steps (4) and(5) for selecting the remaining

montages.

Electrode Recording

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Electrode Recording

The recording is obtained by placing electrodes on

the scalp,

Application of a conductive gel to reduce

resistance.(To reduce interference and minimize the

effect of electrode movement.)

Each electrode is connected to an input of adifferential amplifier (one amplifier per pair of

electrodes), which amplifies the voltage between

them (typically 1,000100,000 times,

The amplitude of the EEG is about 100 V whenmeasured on the scalp, and about 1-2 mV when

measured on the surface of the brain

http://en.wikipedia.org/wiki/Electrodehttp://en.wikipedia.org/wiki/Differential_amplifierhttp://en.wikipedia.org/wiki/Differential_amplifierhttp://en.wikipedia.org/wiki/Electrode

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