General explaining about

EEG

Mehran Ahmadlou 86133001

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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

Bقطبي گيري‌تک .‌اندازه‌(Unipolar‌‌)‌‌‌‌‌‌‌‌‌‌‌‌‌‌‌‌‌‌Aگيري‌دوقطبي‌ .‌اندازه(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

مختلف DELTA : فرکانس‌هاي

هرتز 3تا 0.5عميق بسيار خواب

از کمتر شيرخوارگان است 6در غالب موج ماهدشوار مسائل حل هنگام

زياد دامنه‌ي با :دلتاي

يادگيري ناتوانايي‌هايمغزي صدمات

مختلف THETA : فرکانس‌هاي

هرتز 7تا 4عميق روياي هيپنوتيزم، بي‌هوشي،

خلق و شهودنوجوانان و کودکان

زياد دامنه‌ي با :تتايادگيري ناتوانايي‌هايکند متقابل پاسخاضطراب و افسردگي

خون در اکسيژن کمبود

مختلف ALPHA : فرکانس‌هاي

هرتز 12تا 8کامل هشياري

تعمق و Meditation مطالعه

مي‌شوند ) آشکار بهتر بسته چشم ( با

زياد دامنه‌ي با :آلفاDaydreamers

ماري‌جوانا مصرفبي‌خوابي

مختلف BETA : فرکانس‌هاي

هرتز 22تا 15تفکر

تمرکزمساله حل

زياد دامنه‌ي با :آلفاObsessive-Compulsive Disorder (OCD)

Anxiety Disorders

مختلف GAMMA : فرکانس‌هاي

هرتز 42تا 35و ( ...) مسائل حل ترس، ادراک، زياد ذهني فعاليت‌هاي

متعالي تجارب

• The amplitude of the normal EEG can vary between approximately -100 and +100 µV, and its frequency ranges up to about 40 Hz.

کاربردها

صرع (• )epilepsyتشخيص

مغزي • آسيب‌هاي تشخيص به کمکمغز (– ورم تومورها، ، encephalitis (،mental retardationضربات،

روان‌شناسي • تشخيص‌هاي–schizophrenia ، paranoia مانند مغزي اختالالت از ناشي افسردگي‌هاي ،

آلزايمر و پارکينسونجراحي • اعمال در بيهوشي هنگام مغز فعاليت بررسيخواب • ناهنجاري‌هاي و خواب بررسيمغزي • مرگ تشخيص

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.)