GloNeuro

Virtual laboratory / Brain regions and the whole brain

EEG and event-related potentials

Brain responses to rare and frequent sounds, and the averaging that reveals the P300.

Guided experiment: Recording the P300 with EEG.

EEG and event-related potentials

EEG records electrical activity from the scalp. The response to a single event is small compared with the ongoing activity, so researchers average many trials aligned to the event to obtain an event-related potential, or ERP. In the oddball task, rare target sounds among frequent standard sounds evoke a large positive wave about 300 milliseconds after the sound, the P300 (Sutton et al., 1965; Polich, 2007).

Design the experiment

Questions to investigate

  1. Increase the number of trials. How does the noise in the average change as trials are added?
  2. Make the targets more frequent. What happens to the size of the P300?
  3. Switch artefact rejection off. How do eye blinks distort the average?
  4. Compare electrodes Fz, Cz and Pz. Where is the P300 largest?
  5. How many participants are needed to detect the difference between targets and standards reliably?

In a real laboratory

Participants wear a cap of electrodes, and the contact of each electrode with the scalp is checked before recording. The procedure is explained and written consent obtained. The analysis is planned in advance: how artefacts will be removed, which electrodes and time windows will be measured and how many participants will be tested. Research with people requires approval by an ethics committee (in India, an Institutional Ethics Committee following the ICMR National Ethical Guidelines of 2017; elsewhere, the equivalent body).

How the simulation works

Each trial contains components of fixed shape, distributed across the scalp, whose size and timing vary between participants and between trials. The P300 is larger for targets, smaller when targets are frequent and largest at parietal sites. Background EEG is random activity with more power at low frequencies and an alpha rhythm; eye blinks are added at random and are largest at frontal sites. The simulated difference between targets and standards is large and the data are idealised, so with the default settings the estimated power can reach about 100% with only four or so participants. Real P300 studies are more variable and usually need considerably more participants, planned from effect sizes reported in comparable published work.

  1. Sutton, S., Braren, M., Zubin, J., & John, E. R. (1965). Evoked-potential correlates of stimulus uncertainty. Science, 150(3700), 1187–1188. https://doi.org/10.1126/science.150.3700.1187
  2. Polich, J. (2007). Updating P300: an integrative theory of P3a and P3b. Clinical Neurophysiology, 118(10), 2128–2148. https://doi.org/10.1016/j.clinph.2007.04.019

About the simulations

Each simulator is a simplified version of a published model of cells, signals, instruments or behaviour, and runs in the web browser. The simulations show how the techniques work and how design choices change the results; they do not replace training in a laboratory.

All data are simulated and generated afresh on each run, so results vary between runs, as in real experiments. Nothing is stored or sent: designs and results are lost when the page is closed, unless the protocol is copied or the data file is downloaded.

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