EEG measures the summated electrical activity of neurons, primarily in the cerebral cortex.

Specifically:

  • EEG captures the postsynaptic potentials of large populations of neurons, particularly pyramidal neurons aligned perpendicularly to the cortical surface.
  • These signals reflect the summed synchronous activity of thousands or millions of neurons, as individual neuronal activity alone is too small to detect on the scalp.
  • The detected activity is categorized into different brain wave frequencies, such as:
    • Delta (0.5–4 Hz): Deep sleep.
    • Theta (4–8 Hz): Light sleep, relaxation.
    • Alpha (8–13 Hz): Relaxed wakefulness.
    • Beta (13–30 Hz): Active thinking, focus.
    • Gamma (30+ Hz): Higher-level cognitive functions.

Key Features of EEG:

Because EEG measures summated activity from the scalp, it has excellent temporal resolution (milliseconds) but limited spatial resolution. This makes it more suitable for tracking the timing of brain activity rather than pinpointing specific regions.