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Before you start

The groundwork that makes the rest of the path make sense: where the EEG signal comes from, where electrodes go, how to read a line of MATLAB, and what a spectrum shows.

5 lessons: 4 core, 1 optional

After this station you can:

  • Explain why EEG reflects large synchronized populations, not single cells
  • Locate any electrode from its 10-20 name
  • Run a MATLAB line and read a variable
  • Read a simple spectrum

Lessons

  1. Where the EEG signal comes fromCore10 min
  2. The 10-20 system & electrodesCore10 min
  3. MATLAB basics for EEGLABCore15 min
  4. Signals & frequenciesCore15 min
  5. Designing EEG experimentsOptional15 min

Test yourself

5 questions. Your score stays with you and isn't sent anywhere.

1. What mainly reaches a scalp electrode from brain activity?
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The correct answer: Postsynaptic potentials from millions of parallel pyramidal cells active at the same time

Postsynaptic potentials last tens of milliseconds, so they overlap across many cells. Pyramidal cells are parallel and point toward the surface, so their currents add up instead of canceling. Action potentials are very short, about 1 ms, so they rarely line up across many cells.

Review the lesson: Where the EEG signal comes from

2. Which of these are non-brain sources that can appear in an EEG recording? (Select all that apply)
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The correct answer: Eye blinks and eye movements, Jaw, neck and forehead muscles, The power line in the building

Blinks, muscles and the power line are all artifacts: non-brain signals mixed into the recording, sometimes larger than the brain signal itself. Postsynaptic potentials in the cortex are the main brain signal. You learn to remove artifacts in stations 3 and 4.

Review the lesson: Where the EEG signal comes from

3. The head in the drawing is seen from above, nose up, as in EEGLAB plots. What is the name of the highlighted electrode?A head seen from above with the nose at the top and ears at the sides, with 21 dots for the 10-20 electrodes and no names. One dot is filled in a different color in the middle row from front to back, in the right half of the drawing, between the midline and the ear.
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The correct answer: C4

The electrode is in the central C row, in the right half, and an even number means right, so it is C4. C3 is its mirror on the left, Cz is exactly on the midline, and T8 is farther out at the edge near the ear. The left of an EEGLAB plot is the participant's left, because the head is drawn from above.

Review the lesson: The 10-20 system & electrodes

4. The matrix demo.data has 3 rows and 1280 columns: channels in rows, samples in columns. Which command gives you samples 1 to 5 of the second channel?
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The correct answer: demo.data(2, 1:5)

The first number selects the row (channel) and the second the columns (samples). MATLAB counts from 1, not 0, so 0:4 gives an error. Curly braces are for cell arrays, not matrices. EEG.data in EEGLAB uses the same order: channels first, then samples.

Review the lesson: MATLAB basics for EEGLAB

5. A dataset was recorded at a sampling rate of 128 Hz. What is the highest frequency it can represent?
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The correct answer: 64 Hz

The highest frequency that can be represented is the Nyquist frequency, half the sampling rate: 128 ÷ 2 = 64 Hz. A faster frequency does not disappear; it shows up disguised as a lower one (aliasing).

Review the lesson: Signals & frequencies