This simulation demonstrates how the distance of the neural source from the scalp impacts the distribution of electrical potential and the EEG waveforms recorded at different scalp locations.
Maggie Smith (art)
1. Understanding the EEG Signal:
Return to Simulation
Maria Vennikov (art)
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.
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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.
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.
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.
Use the blue buttons on the right to control the DISTANCE of the dipole from the top of the head.
Drag your cursor along the scale to scroll through the timeline of the simulation.
Start by selecting the distance of the dipole
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 neuralactivity contributing to the dipole. This simulation demonstrates how dipoles
close to the surface of the scalp have a stronger but more focused scalp voltage
distribution. This more focused scalp distribution will be measured by fewer
electrodes, and the amplitude of the signal from electrodes that are aligned with
the near end of the dipole will be very high.