This document provides a detailed overview of electroencephalography (EEG). Some key points: - EEG was developed in the late 19th/early 20th century through studies of brain electrical activity in animals and humans. Hans Berger recorded the first human EEG in 1924. - EEG uses electrodes placed on the scalp to detect electrical signals produced by neuron firing in the brain. It can identify abnormalities associated with conditions like epilepsy, tumors, strokes and encephalopathies. - Quantitative EEG analysis allows measuring brain activity levels in different frequency bands to identify abnormalities in conditions like Alzheimer's, ADHD, autism, depression, OCD and schizophrenia.

1. Electroenchephalography
Dr. Nabajyoti Kalita

2. History
• 1874- Caton recorded spontaneous electrical
activity from live exposed cortices of cats,
rabbits and monkeys
• 1891- Adolph Beck demonstrated that the
dog’s visual cortex produced large electrical
potentials when the eyes were rhythmically
illuminated

3. • 1924-Hans Berger finally succeeded in recording the human
EEG. he also coined the term Electroencephalogram
• In his classic series of 23 papers Berger described many
aspects of human EEG:
1) that brain electrical activity came from neurons and not
blood vessels or connective tissue
2) that waking alpha waves were blocked by eye opening
3) the characteristics of EEG activity change with age, sensory
stimulation, state of consciousness

4. • 1934- Lord Adrian publicly confirmed Berger’s
work and the field of EEG was born
• Despite the fact that EEG originated in
psychiatry, the strongest initial impetus for its
use came from neurology, particularly the
study of epilepsy

5. • But EEG didn’t flourish in psychiatry because
of 2 factors:
1) lack of specificity of EEG abnormalities to
known psychiatric syndromes
2) continuing discovery of EEG abnormalities
correlating with epilepsy, tumors,
encephalopathies, stroke syndromes, and
coma

6. • The difference in electrical potential measured
between any two EEG electrodes fluctuates or
oscillates rapidly
• The earliest EEG recordings involved only one pair
of electrodes, or one channel of recording
• Later 4,8,10,12,16 and even 64 channel recording
machines came into existence

7. Scalp-recorded EEG signals are the
result of summated field potentials
generated by EPSPs and IPSPs in
vertically oriented pyramidal cells of
the cortex
An EPSP in a dendrite produces
electrical negativity in the
immediately surrounding area
The reverse occurs with an IPSP,
generating an electrical positivity
nearby
The summation of EPSPs and IPSPs
is enhanced

8. Limitations of scalp eeg
• Although approximately one-third of the outer
convexity of the cortex may be within reach,
much cortical area consists of mesial, inferior, and
deep buried cortical tissue which is not in the
reach of S-electrodes
• Furthermore, substantial impedance to electrical
conduction from skin, skull, dura, and brain tissue
exists

9. • Weak electrical signals, even those close to
the surface,may escape detection
• Because of the limitations of scalp EEG, a
normal EEG can never constitute positive
proof of absence of brain dysfunction(low
specificity)

10. Electrode Placement
• In 1947,it was decided at an international EEG
congress held in London to standardize the
system of electrode placement
• 10-20 international system of electrode
placement was developed which became
standard worldwide since 1958

12. special electrodes
• Sphenoidal electrodes-
• Nasopharyngeal electrodes

13. montage selection
• In EEG , the way electrode pairs are arranged
for a recording is called a montage
• TWO MAIN TYPES OF MONTAGES:
1)Referential 2)Bipolar

14. • The majority of abnormal cerebral activities tend to appear
at the surface as negative potentials
• A given channel of EEG activity is derived from two inputs
• By convention, the first electrode of a pair constitutes input
1, whereas the second electrode provides input 2
• The direction of the pen deflection is based on whether
input 1 is “more negative” or “less negative than the input
2

15. • If the input 1 is closer to the source of a negative
field and, hence, more “negative” than the input
2, then there is an upward pen deflection
• Conversely, if the input 1 is more distant from the
source of the field than the input 2 and, hence,
less negative than the input 2 then the pen
deflection is downwards

17. sensitivity
• The amplification used in EEG recording is
adjustable and can be increased or decreased
according to the need
• accepted standard sensitivity across
laboratories is 7 µV-7.5µV for each millimeter
of pen deflection

18. frequency filter settings
• Nearly all of the EEG activity that is analyzed for clinical
or research purposes falls within the frequency range of
.5 to 40.0 or 50.0 Hz.
• Extreme lowering of lower range will include unwanted
slow waves generated by skin(artifact)while raising it to
5.0hz will exclude some genuine slow waves of brain
origin(fig.)
• Similarly a too high upper limit will include the unwanted
muscle potential while lowering it down will lead to
exclusion of genuine fast spike discharges of brain
origin(fig.)

19. Special activations
• Certain activating procedures tend to increase
the probability that abnormal discharges,
particularly spike or spike-wave seizure
discharges, will occur
• Medication Activation-alpha-chloralose.
• Hyperventilation- for 1 to 4 minutes,: increase in
generalized medium- to high-voltage synchronous
slow waves in the delta range, which then quickly
subside when over breathing stops

20. • Especially effective in eliciting the classic diffuse
three-per-second spike-and-wave complex of
Absence seizures.
• Photic stimulation-involves placing an intense
strobe light approximately 12 inches in front of
the subject's closed eyes and flashing at
frequencies that can range from 1 to 50 Hz.
• Sleep deprivation- CNS stress produced by 24
hours of sleep deprivation alone can lead to the
activation of paroxysmal EEG discharges in some
cases

21. normal intrinsic frequencies

22. Alpha waves-
• Highly rhythmic,8 to 13 Hz
- dominant brain wave frequency of the normal eyes-closed
wake EEG
- most prominent over the posterior cortex, particularly the
parietal, posterior temporal, and occipital cortex
- occipital region being best suited to show this activity
- alpha can be blocked or attenuated by engaging in visual
imagery, numeric calculation, or almost anything requiring
significant concentration(fig.)

23. • Beta waves- frequency >13hz
- Particularly over frontal-central regions
- The voltage of beta activity is almost always
lower than that of activity in the other frequency
bands
• Theta waves- frequency of 4.0-7.5 Hz
- prominent in the drowsy and sleep tracings
- Excessive theta in wake,suggests a focal
pathological process

24. o Delta waves-frequency 3.5 Hz or less
- a prominent feature of deeper stages of sleep
- The presence of significant generalized or
focal delta in the wake EEG is strongly
indicative of a pathophysiological process
o Gamma waves-high frequency oscillations >30
Hz
- Importance in neurobehavioral disorders

25. • Changes with age- appearance of the EEG tracing
changes dramatically from birth to advanced age
• preponderance of irregular delta activity in the
tracing of the infants
• EEG activity gradually increases in frequency and
becomes more rhythmic with increasing age

26. Artifacts
• Artifacts are electric potentials of nonbrain origin
that are in the frequency and voltage range of
EEG signals and that are detected by scalp
electrodes
• Common artifacts include eye blinks, vertical or
lateral eye movements,muscle potentials from
jaw clenching, perspiration artifacts (galvanic skin
response), and head movement

27. quantitative analysis of eeg
• That is,it involves calculating the amount of EEG
in each frequency band such as alpha,theta,delta
• The amount of EEG in each frequency band is
then displayed on a map of the scalp,this is
known as topographic mapping
• Voltages or other features are displayed with
contour lines or color coding

29. Eeg findings in organic
pathophysiology
• Seizures- The hallmark EEG finding for a seizure
disorder is the generalized, hemispheric, or focal spike
or spike-wave discharge, or both
- Absence seizure is of utmost importance for a
psychiatrist as they are often mistaken for inattention
in children or other functional or organic syndromes
- EEG reveals classic diffuse three-per-second,spike-and-
wave discharges with a multiple spike component(fig.)

31. • Structural Lesions-Structural and space-occupying
lesions are typically associated with focal slowing
in the EEG
• focal slowing may be accompanied by focal spike
activity as well(eg.cerebral abscess)
- If SOL is located deeper into subcortical regions,it
may remain invisible in S-EEG
- An increase in the focal slowing on the repeat
exam might suggest a growing or expanding
lesion
- 90% of cortical brain tumors can be detected by
routine EEG

33. • Closed Head Injuries-Focal slowing is the
expected EEG sequela
- may appear over the site of the trauma or
over a contrecoup location
• Hepatic encephalopathy- classic Triphasic
waves characterized by frontally dominant or
diffuse 1.5- to 3.0-per-second high-voltage
slow waves

34. • Alcohol-increase in the alpha activity typically
accompany alcohol consumption
• Beta activity substantially increased in withdrawal
• Delirium tremens- Excessive fast activity
dominate the EEG tracing
• Delirium from other causes is associated with
generalized slowing

35. Eeg findings in psychiatric disorders
• Q-EEG- recent studies strongly support promise as a
diagnostic and prognostic test for early Alzheimer’s
disease
• Dementia- rarely have normal EEG
- Normal EEG can diagnose Pseudodementia
- Useful in following progression of Alzheimer’s disease
- FTD- may have normal routine EEG

36. • Attention-Deficit/Hyperactivity Disorder-
- 1/3rd of ADHD patients have abnormal routine EEG
- Significant proportion exihibit spike or spike-wave
discharges
- Q-EEG- increased theta activity in frontal lobe regions
- Decrease in beta activity

37. • Autistic Spectrum Disorders-
- 5 per sec temporal-parietal sharp wave
discharges(epileptiform activity)
- Slowing in few patients
- Approximately one-third of children with
autism spectrum disorders develop epilepsy

38. • Mania-Q-EEG-less alpha power and high beta
activity
- Left hemisphere involved more
• Depression-S-EEG- can rule out underlying
medical cause of depression(tumor,cva etc)
- Q-EEG-increase in alpha and/or beta waves
- Alpha activity mainly in left frontal region

39. • Obsessive-Compulsive Disorder-
- S-EEG-widespread increase of slow waves
- Also,epileptiform activities over left temporal
lobe
- Q-EEG -involement of ant.regions of the
scalp(frontal dysfunction)(fig.)

40. Schizophrenia
Q-EEG- delta activity significantly increased in both
eyes open and closed conditions,most
significantly over the ant.cortical regions
- Similarly theta activity increased significantly over
the posterior cortical regions
- increase in slow alpha amplitude over anterior
sites
- increase in slow beta amplitude over anterior
sites in eyes open condition
- reduction of gamma oscillations in patients with
schizophrenia

41. Reference
• Kaplan & Sadock’S Comprehensive Textbook
of Psychiatry
• Electrodiagnosis in clinical Neurology
• Various Internet Sources