From this page you can use a simplified viewer to get an idea of what EEGs look like.
There are two records available
An EEG record consists of a number of 'wiggly lines' (in
this case 8) representing the tiny fluctuating voltages which can
be detected on the scalp and which are related to the activity of
the brain within the skull.
The EEG is here displayed by an 'Applet' which takes some while to load and to prepare the display. The time taken will depend partly on the speed of your internet connection and partly on the particular computer and browser that you are using. It may be anything from a few seconds to a minute or more.
On the left at the top is a button 'Show Montage' which
when clicked causes a diagram to appear (looking down on the head
from above - nose at the top, ears on either side). The small
circles represent the positions of electrodes on the scalp.
Channels 1-8 are connected as shown - ch 1 shows voltages at the front on the right, 2 3 & 4 from progressively more posterior regions and then Ch 5,6,7 & 8 from corresponding regions on the left.
Click 'Hide Montage' to make it disappear.
The 'choice control' at the top on the right - 50
pixels/sec - allows you to contract or expand the timescale of the
For example 100 pixels/sec allows individual waves to be more clearly seen while 20 pixels/sec compresses them, often to a solid mass or with individual waves represented simply by up or down strokes.
The little ticks at the top and bottom of the display represent seconds. At 20 pixels/sec a complete page of 30 secs is shown while if the scale is expanded sub-pages of 10 or 5 seconds are indicated by vertical dotted lines.
The filled-in portion of the red bar at the bottom
indicates the relationship of the displayed portion to the whole
record. (Ordinary 'Clinical EEG' records have a typical duration of
10-20 minutes. The examples show only about 1 minute.)
Click on this bar to move the displayed portion to include the click position or drag the filled-in portion.
The three buttons at the bottom on the left allow you to scan through the record.
Note: A 'Page' is 30 seconds long. If a page is too large to be shown on the screen it is divided into sub-pages 10 seconds or 5 seconds long.