basic knowledge for neurologists

1. Dr Mohammed Mahdy,
MD

2. To learn together
FIRST
One flower can give an odour enough than a bouquet
But can’t give the colorful collection
SECOND
Our aim and objectives

5. For the recording of EEG we need
1. Electrodes—To pick up the brain electrical wave activity
and their attached wire to connect with the EEG
machines.
2. Amplifiers—To amplify these micro volts amplitude waves.
3. Filters—To filter out unwanted (artifacts) waves.
4. Writing units—To record these waves on paper.

11. 1. Scalp electrodes are commonly constructed of discs of silver prepared with
chloride salts.
2. Electrode placement requires scalp cleaning, abrasion, and electrical
contact with the use of a conductive gel.
3. Neatness counts: Patient hygiene, sweating, excess or sparse electrode gel,
and poor scalp preparation all may adversely affect electrode impedance.
4. The EEG technologist must document identification of electrode artifacts
and their attempted correction.

13. RULES5

14. 1 The 10–20 International System of Electrode
Placement, where each electrode is 10–20%
away from a neighboring electrode

15. 2 Electrodes placed on the left side of cerebral
hemisphere are given odd numbers (e.g., Fp1,
T3) while right sided electrodes have even
numbers (e.g., Fp2, T4).
The name includes the first letter of the general
area of skull where electrode is placed and
reveals lobe of the brain being recorded.

16. BLAH
BLAH
BLAH
BLAH
B
BLAH
BLAH

18. Fp1, 2—prefrontal
F3, 4—frontal
C3, 4—central
P3, 4—parietal
O1, 2—occipital
F7, 8—anterior temporal (records
activity from anterior temporal region
but placed on frontal bone)
T3, 4—mid-temporal
T5, 6—posterior temporal
Fz—front vertex
Cz—central vertex
Pz—parietal vertex
(z= zero)
A1, 2—ear

21. Filters
A circuit which permits only the necessary signal to pass by varying the
frequency response of an electric current is called filter.
It excludes very slow and very fast activity and select the spectrum of
frequencies which has the greatest clinical significance.
Filters should be used in such a way that they do not eliminate spike/ sharp
wave activity. It should not be used to clean up the artifacts and produce a
pretty record.

22. Low-frequency filters (LFFs) or
high-pass filters
In an LFF, there is marked
attenuation of slow
potentials below the cutoff
frequency (such as those
caused by sweat artifact,
respirations, and tongue
movement), with little effect
on rapid potentials such as
spikes or muscle artifacts.
High-frequency filters (HFFs) or
low pass filters
This circuit attenuates
undesirable high frequencies
(e.g., muscle action potentials)
and passes low frequencies

24. Sensitivity
The sensitivity of each channel refers to the amplitude of the
display produced by the received signal. The measurement
is expressed in voltage per deflection. Standard sensitivity
is 7 μV/mm.
The sensitivity is adjusted to see appropriate waveforms . If
waveforms are of high amplitude, sensitivity should be kept at 10
uV/mm. Higher numeric value of sensitivity mean lower
sensitivity and vice versa

25. AMPLIFICATION
the simple amplifier. Input from a single active
electrode is conducted to the amplifier and
compared with ground (earth). Thus, the output
consists of the potential difference between the
active electrode and ground. Electrocortical
potentials, as well as other environmental
potentials affecting the electrode (e.g., 60 Hz
interference), are displayed in the output.
In differential amplification, signals from two
active leads are conducted to the amplifier, thus
measuring the potential difference between the
two. In this case, any signal that affects both
inputs identically (say 60 Hz) will result in no
potential difference and thus will not be
displayed or be much reduced. This
phenomenon is termed in-phase cancellation.

28. Unipolar recording

29. Bipolar recording

36. Localization

37. Localization
T8

38. Localization
T8
Phase
reversal

49. P 8

50. Montages of EEG

54. N
11 channels due to small head size
Frontal and parietal channels are usually omitted.

56. How to benefit
from montages?

62. 1. Isopotential channels
can result from either
being equally uninvolved
by a focal discharge or
from being equally
involved.
2. Focal discharges that
occur at the end-of-chain
may show no phase reversal
on a longitudinal bipolar
montage.