Eeg presentation for studying and understanding

Electroencephalogram
Electroencephalogram

EEG
Electro-encephalogram:
Representation of the bio-potentials
generated by the brain.
Electro-encephalography:
Instruments to record these bio-
potentials.

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

The Beginnings of Clinical
Neuropsychology
 At the time this was considered cutting edge, with Berger’s
discoveries spawning the field of clinical neuropsychology.

EEG-Definition
 The electroencephalogram (EEG) is a measure of brain
waves.
 It is a readily available test that provides evidence of
how the brain functions over time.
 The electroencephalogram (EEG) is a medical test used
to measure the electrical activity of the brain.

EEG records brain waves
It doesn't read minds or measure IQs.
Instead, it's used to detect the level of
electrical activity in the brain.
Your brain cells communicate by electrical
impulses, and an EEG measures and records
these electrical impulses to detect anything
abnormal.
Definition-…..ctd

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

EEG - USE
 Confusion
 Tumors
 Long-term difficulties with thinking or
memory
 Weakening of specific parts of the body
 To determine brain death
 Sleep disorders

EEG ACTIVITY
 The rhythmic activity of the brain is
designated 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

Beta activity is a normal activity present when
the eyes are open or closed.
It tends to be seen in the channels recorded
from the centre or front of the head.
 Some drugs will increase the amount of beta
activity in the EEG.
Associated with active, busy or anxious thinking
and active concentration.
BETA ACTIVITY

ALPHA ACTIVITY
Alpha activity is also a normal activity
It is only seen when the eyes are closed and
should 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

THETA ACTIVITY
Normal and abnormal activity depending on the
age and state of the patient.
It is associated with drowsiness
However it can also indicate brain dysfunction
if it is seen in a patient who is alert and awake.

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.

EEG Measurements
 An EEG is performed by picking up signals from the
scalp by using 23 active electrodes.
Amplitude: 10 microvolts to 100 microvolts.
Frequency: 1Hz to 100 Hz.
ELECTRODES:
Surface,Pad,silver.

EEG Measurements
An EEG is a recording of electrical signals from the
brain made by hooking up electrodes to the patient's
scalp.
These electrodes pick up electric signals naturally
produced by the brain and send them to galvanometers
(instruments that detect and measure small electric
currents)
Galvanometers are in turn hooked up to pens, under
which graph paper moves continuously. The pens trace
the signals onto the graph paper.

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 a
person'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.

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.
Electrode Board/Head box has 23 jacks for 21 active
electrodes,2 reference electrodes and a ground
electrode.

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,tongue
and 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.

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.

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 lin etc.
Faulty electrode application.
Patient movement.
Muscle artifacts.(from gritting teeth or restlessness.
Blinking of eyes.

EEG-Block Diagram
Balance Bridge
Type Differential
stage
Differential
Amp
Pre
AMP
50Hz
Filter
Lo-Linear
And
Hi-Linear
Filter
Power
Amp

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 a
differential amplifier (one amplifier per pair of
electrodes), which amplifies the voltage between
them (typically 1,000–100,000 times,

Electrode-Amplifier
EEG 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.

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.

Montage
The manner in which pairs of electrodes
are connected to each amplifier of the EEG
machine is called a montage.
Each montage will use one of the
following standard recording derivations,
Monopolar derivation
Bipolar derivation

Monopolar Recording
Common reference derivation
 Each amplifier records the difference between a
scalp electrode and a reference electrode.
 The same reference electrode is used for all
channels.
 Reference electrode placed somewhere along the
scalp midline, or a reference that links both earlobe
electrodes.

Bipolar Recording
The electrodes are connected in series to an equal
number of amplifiers.
Electrodes linked together usually in straight lines
from the front to the back of the head or transversely
across the head.
Example, amplifier 1 measures the difference between
electrodes A and B, amplifier 2 measures the difference
between B and C, and so on.

EEG MACHINE
EEG MACHINE CONSISTS OF THREE
PARTS:
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 of
channel amplifier modules and the master
control panel.

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 setting –70 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
1. All channel sensitivity-
• To increase or decrease the sensitivity of all
channels.
• 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 volts
4. CAL push button-For giving a CAL. Pulse.
5. CAL/USE: For selecting CAL or record mode.

MASTER CONTROLS…ctd
6. All channel montage selector:For automatic
electrode selection.
7. Electrode Resistance test- For measuring
electrode impedance.
8. Individual electrode selectors- These selectros are
used 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 and
the amplifier inputs.

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 cahrt speed.
It has four selections. The standard speed –
30m/sec.

CHART DRIVE
3. Stop/Chart/Chart-pen:-
In STOP position the recording pens and the
paper 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
1. Turn the machine ON and allow it to warm up for
15 minutes.
2. Load the machine with paper and fill the
inkwheels with ink.
3. Make sure that the base line of all pens is
centered.
4. Set all amplifier controls at standard setting.

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
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 the
chart drive to STOP position.
6. Repeat steps (4) and(5) for selecting the remaining
montages.

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 a
differential amplifier (one amplifier per pair of
electrodes), which amplifies the voltage between
them (typically 1,000–100,000 times,
The amplitude of the EEG is about 100 µV when
measured on the scalp, and about 1-2 mV when
measured on the surface of the brain

Eeg presentation for studying and understanding

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Eeg presentation for studying and understanding