Use the grouping of buttons to
select the angle of the dipole’s
Press “PLAY” in order to run through
the timeline and see the results
Drag your cursor along the scale
to scroll through the timeline of the
3. Understanding the EEG Signal:
This simulation demonstrates how orientation of the neural source in relation to the scalp impacts the distribution of electrical potentialand the EEG waveforms recorded at different scalp locations.
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As the dipole activates, the resulting EEG recording will display in the fields to the left of the head. This simulation demonstrates how changing the distance of the dipole from the scalp affects the scalp voltage distribution and EEG signal.
During post-synaptic potential activity, the change in ion concentration surrounding the cells result in a separation of charge in the extracellular fluid, creating a dipole. In the dipole symbol pictured on the right, the round end represents the source and the color represents polarity (blue = negative; red = positive). In this simulation, the dipole represents summed activity from a group of neurons that are functionally related and are simultaneously active.
As the dipole activates, the voltage at the scalp is represented by a series of concentric circles, with deeper colors representing stronger voltage. Similar to a flashlight shining on a surface, the scalp voltage is strongest at the scalp location that is aligned with the dipole, and its strength weakens as the signal is dispersed.
Electrodes placed on the scalp measure voltage changes with millisecond precision. In this demonstration, there are 5 electrodes, labeled T7, C3, CZ, C4, and T8, placed on the scalp from ear to ear.
Post-synaptic activity creates a difference in charge in the extracellular liquid,
resulting in a dipole that can be measured by electrodes placed on the scalp.
The strength and polarity (direction) of the signal recorded at each electrode
will depend on the electrode location with respect to the source of the neural activity
contributing to the dipole. This simulation demonstrates how the orientation of
the dipole in relation to different areas on the scalp affects the polarity of the signal
recorded at various electrode locations. As reflected in this simulation, one electrode
location can pick up a positive signal or a negative signal, depending on how the dipole
is oriented in relation to that specific electrode location.