What is EEG study?
Electroencephalogram (EEG) is a recording of the electrical activity emitted by the brain through a different number of electrodes (small metal disks) that are attached to the scalp at particular places, using contact paste. The emitted by the brain electrical activity is led to an amplifier through electrodes and then to a computer system where the recording is processed and analyzed. The survey is completely painless and safe.
Electroencephalography examines the functional brain activity and is one of the neurophysiological methods suitable for the examination of pathophysiological changes when having diseases of the central nervous system as well as to evaluate the therapeutic effect of the applied medicines. The methods are non-invasive, non-traumatic, painless and reliable for detection of functional changes.
Electroencephalogram (EEG) is a record of the total brain electrical activity through electrodes attached to the scalp. The locations of the electrodes are strictly defined according to the international system 10-20, unified for all laboratories worldwide.
The number of registering electrodes varies from 2 to 256 units. Depending on their location on the scalp they may be prefrontal, frontal, central, parietal, occipital, temporal, ear and sagittal. Each electrode is connected through wire cable to a differential amplifier that amplifies the potential difference between two electrodes to 100 000 times. The electrodes record mainly summed electrical charges of the underlying cortex (cortex), but can capture also potentials generated elsewhere in the brain or different structures outside the brain.
The normal electrical brain activity is composed of repetitive rhythmic fluctuations. Several basic rhythms can be distinguished depending on the frequency of fluctuations per second are divided:
Delta rhythm – 0,5-3,5 Hz fluctuations per second. There are normal in childhood and in phases of deep sleep when talking about adults.
Theta rhythm – 4-7,5Hz fluctuations per second. There are normal in childhood and in some of phases of sleep when talking about adults. Their occurrence is associated with pathological processes in the brain.
Alpha rhythm – 8-13 Hz fluctuations per second. Best is being registered when the patient closes his/her eyes.
Beta rhythm – 3-30 Hz oscillations per second.
After analog-to-digital conversion and the corresponding frequency filtering of 0.5-70 Hz (hertz), the fluctuations of brain potential are recorded in computer system. The record is subject to computer processing and analysis.
Normal EEG activity
Normal rhythms are different for different age groups and they are changing with the age. Usually there is one dominant frequency for each age. With infants it is in Delta-Theta range (3,5-5 Hz), with children it is Theta-Alpha range (5-8 Hz), and with adults the frequency is in the Alpha range (8-10 Hz). The main rhythms are accelerated with age advancement and Alpha rhythm prevails in the age of 18-20 years. Delay occurs most often during sleep and with elderly people.
Abnormal EEG activity
Abnormal EEG is characterized by specific rhythms / waves (findings). EEG findings are used to assist the diagnosis of neurological disorders, such as trauma of the central nervous system, brain tumors, cerebrovascular diseases, inflammatory diseases, impaired consciousness, epilepsy.
The existence of findings in the EEG which cannot be associated with already known clinical condition is alarming and requires urgent clarification of its origin. Up to 60% of brain tumors are registered even before the onset of clinical symptoms.