Last update: September 16, 2022
By BrainMatters

The EEG signal generated by the brain is amplified before it reaches the computer. In the computer, a software is programmed that knows exactly when a stimulus is offered. The activity that is visible immediately behind this stimulus presentation is associated with the stimulus.  However, a lot of other things are also visible in the EEG. These are things that have nothing to do with responding to a stimulus, such as blinking one's eyes or activating muscles in the neck. To counteract this, the same stimuli can be presented very often in succession. After the examination, the pieces that belong to the stimuli are laid on top of each other and averaged. After averaging, a smoother line comes out that has been purified for noise. Such an averaged piece is called an Event-related Potential (ERP).

There are several components to a 'standard ERP', these are also called peaks. The first components of the ERP are automatic reactions of the brain associated with the detection of a stimulus. The later components are caused by the need to make a response. A component is described in a certain way in the literature. This makes it easier to understand exactly what is meant, but of course you have to know the names.

  • Polarity; is the component positive or negative
  • Latency; how long after the presentation of the stimulus does the component appear
  • Topography; on which electrode is the component mainly found

A positive component at 300 ms after stimulus delivery, in the parietal lobe for example, is indicated by P3-P300.

Now that we have this basic information, we can also look at the application of EEG. With the help of EEG we can distinguish different processes from each other. For example, when the stimulus is blurred, this can be seen in the EEG signal because the early components (P1, N1 and P2) have a longer latency, compared to a control condition. In the same way, you can change cognitive variables (for example, you can rotate the stimulus). You can then see exactly which components are affected by different processes.

Different 'special' components can also be found in an EEG signal. An example is the ERN, which stands for Error Related Negativity. As the name suggests, this is a negative component that is found after an error has been made in the task. This component is thus a reflection of becoming aware of the mistake that was made, and is also called the 'oops-reaction'.

Author: Myrthe Princen (translated by Thomas von Rein)

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