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1. Understanding the EEG Signal:  Distance

    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.

Introduction

Jake Cardwell

Created by

Maggie Smith (art)

1. Understanding the EEG Signal:  Distance

Return to Simulation

Maria Vennikov (art)

Eliz Akin

C3

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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T8

Dipoles

T7

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.

C4

EEG Recording

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. 

Scalp Distribution

Electrodes

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.  

Middle

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Drag your cursor along the scale to scroll through the timeline of the simulation.

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Instructions

PAUSE

Instructions

Conclusion

TIME (ms)

Introduction

Start by selecting the distance of the dipole

PLAY

RESET

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.

Conclusion

Simulation