Brain-machine interface, Electronics, Instrumentation, Medicine

How electroencephalogram works?

In this post is shown what it is and how the device used in electroencephalogram works. This technique is important in research and medical diagnostic.

Brain waves

The brain emits brain waves. Are produced by electric pulses running through neurons and show the mental state.

  • Delta waves: Have frequency between 0.5 and 3 Hz. Are the ones of highest amplitude and lowest frequency. Are present in deep meditation and dreamless sleep.
  • Theta waves: Frequencies are between 4 and 7 Hz. Are waves of subconscious. Appear in meditation and lucid REM sleep.
  • Alfa waves: Have frequency from 8 to 12 Hz. Appear when the person is lucid, calm and relaxed.
  • Beta waves: Frequency from 13 to 37 Hz. Has significant presence in the normal state of conscious. When the person is alert, focus and solving problems.
  • Gamma waves: Frequencies are between 38 and 100 Hz. The brain waves of highest frequency. Are very present in processes of memory, learning and information processing.

  • Also exist the infralow waves or epsilon. Has frequency lower than 0.5 Hz. Little is know about these waves. Are hard to detect and are present in advanced state of meditation.

The electroencephalogram device

Metallic electrodes, made of tin, gold or silver and coated with silver chloride, in disc shape, are fixed in the scalp with a conductive gel.

Each electrode pair is a channel. The brain`s electrical signals are very weak with microvolts of amplitude, an electronic amplifier is necessary to amplify the channel`s signal, it is an circuit with operacional amplifiers, resistors and capacitors, like this example below.

Then, the signals pass through electronic filters to reduce interferences. This is a 32 channel amplifier with terminals to connect electrodes.

In the old days, the signals moved a galvanometer which had pointers writing in a paper surface moving in a constant speed.

Today electrical signals are digitalized, displayed and stored in a computer or oscilloscope.

This device can measure the quantity of brain waves. Some diagnostics are made measuring the quantity of brain wave types. The excess or lack of certain types of brain waves indicates disorders or mental states. A multichannel electroencephalogram can indicate a problem in a brain region.

Brain topography of EEG

The increase of capacity to process a great number of data allowed the brain topography. A bigger number of electrodes is used and a software creates a image showing topography of electrical activity.

With this technique, it is possible to take many images and obtain an animation in real time of brain`s electrical activity. Identifying brain parts responsible for determined activities.


About Pedro Ney Stroski

Leave a Reply

Your email address will not be published. Required fields are marked *