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General explaining about
EEG
Mehran Ahmadlou 86133001
‫تاريخچه‪ :‬در سال ‪ 1924‬براي اولين بار توسط فيزيولوژيست آلماني «هانس برگر» ثبت و نامگذاري شد‪.‬‬
Why neocortex ?
•
First, the activity of one neuron is too small to be recorded. To be visible on
the scalp, electrical activity must involve thousands of neurons acting
synchronously. The neocortex has a high density of neurons, which
facilitates their synchronous activation.
•
Second, it is not enough to act synchronously. Electrical activity is visible
only if the activity of the underlying neurons adds up. To add up the activity
must be generated by parallel neurons. The neocortex is composed of
pyramidal cells aligned in parallel.
•
Third, the electric and magnetic field decrease with the distance from the
source. The neocortex is closer to recording sensors.
the 10-20 international system
•
It is based on anatomical location and on percentage of distance among
these points giving the 10 or 20% in the system name. The original 10-20
system has only nineteen electrodes but has been extended to
accommodate more than 200 electrodes.
128 channels
•
In this system the electrodes' locations are related to specific brain areas.
For example, electrodes C3 and C4 are above the motor cortex
F (frontal), C (central), T (temporal), P
(posterior), and O (occipital).
•
Each EEG signal can therefore be correlated to an underlying brain area.
•
A better correlation can be obtained by registering the electrode's locations
with MRI of the subject's head.
•
Electrical Recording with Differential Amplifiers :
Reference and “ Active ” Electrodes
Bipolar and “ Monopolar ” Montages
Bias of the Average Reference
‫‪ .B‬اندازهگيري تکقطبي (‪)Unipolar‬‬
‫‪ .A‬اندازهگيري دوقطبي (‪)Bipolar‬‬
Characterization of EEG Activity
 General EEG frequencies :
 eta: 13-30 Hz (desynchronized)
 alpha: 8-12 Hz (synchronized)
 theta: 3.5-7.5 Hz (synchronized)
 delta: < 3.5 Hz (synchronized)
 Lower frequencies are usually higher amplitude
(“synchronized”) activity
‫‪DELTA‬فرکانسهاي مختلف ‪:‬‬
‫‪ 0.5‬تا ‪ 3‬هرتز‬
‫خواب بسيار عميق‬
‫در شيرخوارگان کمتر از ‪ 6‬ماه موج غالب است‬
‫هنگام حل مسائل دشوار‬
‫دلتاي با دامنهي زياد‪:‬‬
‫ناتواناييهاي يادگيري‬
‫صدمات مغزي‬
‫‪THETA‬فرکانسهاي مختلف ‪:‬‬
‫هرتز‪ 7‬تا ‪4‬‬
‫بيهوشي‪ ،‬هيپنوتيزم‪ ،‬روياي عميق‬
‫شهود و خلق‬
‫کودکان و نوجوانان‬
‫تتا با دامنهي زياد‪:‬‬
‫ناتواناييهاي يادگيري‬
‫پاسخ متقابل کند‬
‫افسردگي و اضطراب‬
‫کمبود اکسيژن در خون‬
‫‪ALPHA‬فرکانسهاي مختلف ‪:‬‬
‫‪ 8‬تا ‪ 12‬هرتز‬
‫هشياري کامل‬
‫‪Meditation‬مطالعه و تعمق‬
‫) با چشم بسته بهتر آشکار ميشوند (‬
‫آلفا با دامنهي زياد‪:‬‬
‫‪Daydreamers‬‬
‫مصرف ماريجوانا‬
‫بيخوابي‬
‫‪BETA‬فرکانسهاي مختلف ‪:‬‬
‫هرتز‪ 22‬تا ‪15‬‬
‫تفکر‬
‫تمرکز‬
‫حل مساله‬
‫آلفا با دامنهي زياد‪:‬‬
‫)‪Obsessive-Compulsive Disorder (OCD‬‬
‫‪Anxiety Disorders‬‬
‫‪GAMMA‬فرکانسهاي مختلف ‪:‬‬
‫هرتز‪ 42‬تا ‪35‬‬
‫فعاليتهاي ذهني زياد )ادراک‪ ،‬ترس‪ ،‬حل مسائل و ‪(...‬‬
‫تجارب متعالي‬
•
The amplitude of the normal EEG
can vary between approximately
-100 and +100 µV, and
its
frequency ranges up to about 40
Hz.
‫کاربردها‬
‫•‬
‫•‬
‫•‬
‫•‬
‫•‬
‫•‬
‫تشخيص صرع )‪(epilepsy‬‬
‫کمک به تشخيص آسيبهاي مغزي‬
‫– ضربات‪ ،‬تومورها‪ ،‬ورم مغز )‪،mental retardation ،(encephalitis‬‬
‫تشخيصهاي روانشناسي‬
‫– ‪ ،paranoia ،schizophrenia‬افسردگيهاي ناشي از اختالالت مغزي مانند پارکينسون و‬
‫آلزايمر‬
‫بررسي فعاليت مغز هنگام بيهوشي در اعمال جراحي‬
‫بررسي خواب و ناهنجاريهاي خواب‬
‫تشخيص مرگ مغزي‬
Figure 7.5 (a) Four types of
EEG waves.
Figure 7.5 (b) When the eyes
are opened, alpha waves
disappear.
Figure 7.5 (c) Different types of epilepsy yield abnormal waveforms. (From Guyton, A. C.
Structure and Function of the Nervous System, 2nd. Ed. Copyright  1972 by W. B. Saunders. Reprinted by
permission of W. B. Saunders.)