Quiz 02: Neurons and electricity: where the EEG signal comes from

8 questions on lesson 2. Nothing is timed. Pick one answer for each, then check them.

1. Which electrical events make most of the scalp EEG signal? Single neurons firing on their own Action potentials (spikes) Postsynaptic potentials of many neurons The heartbeat

2. Why do action potentials hardly show up in scalp EEG? They last about 1 ms, so spikes from different cells rarely overlap The skull blocks them completely They are too large for the amplifier They only happen during sleep

3. Which cells are the main source of the EEG signal? Cells whose branches point in all directions Pyramidal neurons in the cortex Cells in the cerebellum Red blood cells

4. In this lesson, what is a dipole? Two electrodes placed next to each other A pair of opposite charges, like the two ends of a battery A neuron with two branches A signal that repeats twice a second

5. How much cortex usually has to be active together for a spike to show on the scalp? About 1 cm² About 200 cm² About 0.1 cm² About 10 to 20 cm²

6. About how many neurons are in the human cortex? About 16 billion About 16 million About 860 billion About 86 billion

7. Which dipoles does EEG pick up best? Ones that lie sideways, in the grooves between folds Ones that point straight out towards the scalp Ones that point in random directions Ones deep in the brainstem

8. 100 equal signals are added up. About how much bigger is the sum when they are in step, compared with random timing? About 100 times bigger About 10 times bigger About 2 times bigger The same size

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