Electroencephalography is the technique used to acquire electrical signals of brain through electrodes which are placed by certain montage. Different wave patterns can be observed which is useful in detecting any abnormal conditions or neurological brain disorders in human beings. There is broad future scope for medical research and creating EEG based equipments for real time applications.
2. Introduction
Electroencephalography is a technique that
records the electrical activity of the brain
During an EEG test, small electrodes like cup or
disc type are placed on the scalp
They pick up the brain's electrical signals and
send them to a machine called
electroencephalogram
It records the signals as wavy lines on to a
computer screen or paper in order of microvolt
2
3. History of EEG
In 1875, Sir Richard Caton presented his findings
about electrical phenomena of the exposed
cerebral hemispheres of rabbits and monkeys
In 1890, Sir Adolf Beck published an
investigation of spontaneous electrical activity of
the brain of rabbits and dogs
In 1924, Sir Hans Berger recorded the first
human EEG
3
4. Why EEG is used
An EEG is mainly used when there is a need to
diagnose and manage epilepsy
It can also be used to investigate other
conditions such as encephalitis, dementia, head
injuries, brain tumors, hemorrhage
An EEG can identify areas of the brain that are
not working properly
EEGs are also used to determine the level of
brain function in people who are in a coma
4
5. Parts of Brain
Cerebrum
Frontal Lobe
Parietal Lobe
Temporal Lobe
Occipital Lobe
Cerebellum
Brain stem
Parts of brain
5
6. Source of EEG activity
Neurons are electrically
charged by membrane
transport proteins that
pump ions across their
membranes
When the wave of ions
reaches the electrodes on
the scalp, they can push or
pull electrons on the metal
of the electrodes
Push or pull difference
measured as voltage across
time is referred as EEGElectrode on scalp
6
7. Types of electrode placement
EEG electrodes placed
separately on scalp
EEG electrodes mounted as
special band on head
7
10. Types of EEG
• Around 20 electrodes are stuck to the scalp using a special
paste and EEG signals are recorded
Routine EEG
• The EEG tracing will be recorded along with the heart rate,
airflow, respiration, oxygen saturation and limb movement
Sleep EEG
• It involves recording the brain activity throughout the day and
night
• A small portable EEG recorder is clipped on to the clothing
Ambulatory EEG
10
11. Types of EEG electrodes
11
Ear clip electrode
Disk electrodes
Intracortical electrodes
12. Electrode
Montage
Selector
Hi-pass Low-pass Notch Sensitivity
Amplifiers
Filters
Electrode
test/calibrate
Jackbox
Analog to digital
converter
Oscilloscope Computer
Chart
drive
Ink-writing
oscillograph
Writer unit
EEG
Subject
Electrodes
Schematic diagram of an EEG machine
12
13. Montages
Sequential montage
• Each channel represents the difference between two
adjacent electrodes
Referential montage
• Each channel represents the difference between a
certain electrode and a designated reference electrode
Average reference montage
• The outputs of all of the amplifiers are summed and averaged
Laplacian montage
• Each channel represents the difference between an electrode
and a weighted average of the surrounding electrodes
13
14. Wave patterns
Delta waves
Frequency range 0.5-4 Hz
Slow-sleep wave for adults
Theta waves
Frequency range 4-7 Hz
Drowsiness in older children and adults
14
15. Alpha waves
Frequency range from 7-14 Hz
Closing of the eyes, relaxation and attenuation with
eye opening or mental exertion
Mu rhythm
Frequency range from 8-13 Hz
Shows rest-state motor neurons
15
16. Beta waves
Frequency range 15 – 30 Hz
Active, busy, or anxious thinking, active concentration
Gamma waves
Frequency range approximately 30–100 Hz
Perception that combines two different senses, such as
sound and sight
Short-term memory matching of recognized objects,
sounds, or tactile sensations
16
18. EEG Results
Normal EEG Abnormal EEG
A brainwave pattern called
alpha rhythm should be
seen when sitting quietly
with eyes closed
EEG results are
often normal because
recording a person's brain
activity during the times it
is abnormal is difficult
People with epilepsy may
have abnormal brain
activity detected
People who do not have
epilepsy may also have an
abnormal EEG result
indicating any other
disorder
18
19. EEG Artifacts
• Mains voltage of 110/230 volts, exceeds the EEG's 50
to 100 microvolts by 126dB
• Amplifier notch filters are designed to suppress a
certain amount of mains interference
Mains
Interference
• Eye-induced artifacts - eye blinks, eye movements
• ECG and EMG induced artifacts
• Glossokinetic artifacts
Biological
Artifacts
• Movement by the patient, or even settling of the
electrodes
• Presence of an IV drip that can cause rhythmic, fast,
low-voltage bursts, which may be confused for spikes
Environmental
Artifacts
19
21. Artifact correction
Independent component analysis techniques
have been used to correct or remove EEG
contaminants
This would result in clean EEG by nullifying
(zeroing) the weight of unwanted components
Surface Laplacian has been shown to be
effective in eliminating muscle artefact
21
22. Risks and Precautions
Slight redness may occur in the locations where
the electrodes were placed
In rare cases, the cleaning liquid or paste may
cause temporary skin irritation
The person is instructed not to take food that
contains caffeine
Not to have oiled hair on the day of test
22
23. Advantages
Hardware costs are significantly lower than those of
most other techniques
EEG has very high temporal resolution, on the order
of milliseconds rather than seconds
Extremely non-invasive
EEG is silent, which allows for better study of the
responses to auditory stimuli
EEG does not involve exposure to high-intensity
(>1 Tesla) magnetic fields
23
24. Disadvantages
Low spatial resolution on the scalp
EEG determines neural activity that occurs
below the upper layers of the brain poorly
Often takes a long time to connect a subject to
EEG
Signal-to-noise ratio is poor
24
25. Uses of EEG
Clinical Use
Distinguish epileptic seizures from non-epileptic
seizures, syncope (fainting) and sub-cortical
movement disorders
To serve as an adjunct test of brain death
To determine whether to use anti-epileptic
medications
Research Use
Cognitive science, cognitive psychology, neuro -
linguistics and psycho physiological research
25
26. Some more uses
Investigate epilepsy and locate seizure origin
Monitor cognitive engagement (alpha rhythm)
Monitor human and animal brain development
Test epilepsy drug effects
Test afferent pathways (by evoked potentials)
Investigate sleep disorder and physiology
Control anesthesia depth
26
27. Modern clinical EEG system
It is a 36 channel cEEG system
The system incorporates digital
video with the traditional EEG
It is unaffected by electrical,
radio and magnetic interference
27
28. Research on infant attention
The goal of the research was to examine the
role of the brain in development of infant
attention
Baby with EEG recording net that
measures 128 channels of EEG
activity
Pictures and movies with sounds
were shown to check baby’s
response
infantlab.psych.sc.edu
Baby with EEG
28
30. Software for EEG
EEG recording can be analyzed using various
programs
EEGLAB
Fieldtrip
NBT
Tucker-Davis Technologies
Brainvision Analyzer
30
31. Companies
Some of these companies have built commercial
EEG devices
NeuroSky
OCZ Technology
Square Enix
Mattel
Emotiv
31
32. Future scope
Telepathic Helmets
Neuroheadset
EEG has future advances in clinical, research, military & gaming industry
Honda is attempting to develop a system to enable an operator to control
its Asimo robot using EEG
Future Portable EEG
32
33. References
Handbook of Biomedical Instrumentation-R.S Khandpur, 2nd edition
Haas, L F (2003). "Hans Berger (1873-1941), Richard Caton (1842-
1926), and electroencephalography". Journal of Neurology,
Neurosurgery & Psychiatry
www.nhschoices.com
infantlab.psych.sc.edu
www.ece.mcmaster.ca
guile3d.com
viasyshealthcare.com
24megabytes.com
tuckerdavistechnologies.com
thefuturist.com
E. Niedermeyer, F. H. Lopes da Silva. 1993. Electroencephalography:
Basic principles, clinical applications and related fields, 3rd edition,
Lippincott,Williams &Wilkins, Philadelphia
33