Native record and provoking tests

Creating Native Record

What is meant by that? However the term describes the creation of an electroencephalogram using the method of electroencephalography. First observed over 80 years ago it measures and records electrical signals, created by the neurons of the cortex, using small disks of silver chloride as electrodes attached to the scalp. In routine examination 16 channels are measured using unipolar electrode connection, with the reference electrode usually attached to the ear

EEG signals are very low, between 5 to 100 µV. Recording them on an electroencephalogram, not only voltage amplitude is to be seen but also the frequencies, which lead to the term brainwaves, both of them dependent on the mental activity of the brain examined. A normal EEG can look like this:

You can distinguish 4 main types of waves:

Beta F: 15-20Hz, A: 5-10 µV (subject in alert state)

Alpha F: 8-13 Hz, A: > 50 µV (subject in relaxed state)

Theta F: 4-7 Hz, A: < 50 µV (subject in deep sleep, children)

Delta F: 0.5-4 Hz, A: 100 µV (pathological)

Why is this method of such a great importance? Even though the synchronicity between the actual brain activity and the measured signals on the surface is still of unknown extent it allows the diagnosis of various malfunctions of the cortex, such as epilepsy, brain tumors, parkinson, learning disabilities, migrane and to determine the brain activity (death) during coma. Besides that, you can measure the signals that result from the brain receiving external stimuli, evoked potentials. Thus is performed by

Provoking Tests

By placing a strobe light in the vision of the subject during brainwave measurements a change in the EEG can be seen, made possible by simple computer programs which extract only the visually evoked potential. The stimulations happens in primary visual cortices and secondary areas, usually recorded from occipital scalp overlying the calcarine fissure.