electroencephalogram
Summary
An electroencephalogram (EEG) records the brain's electrical activity through scalp electrodes, mainly from summed postsynaptic potentials in the cortex. Most testable: as sleep deepens, waves slow and grow taller (beta, alpha, theta, delta), while REM sleep looks like waking.
Detail
Meaning: An electroencephalogram (EEG) is a recording of the brain's electrical activity made with electrodes on the scalp. The signal reflects summed postsynaptic potentials of large groups of cortical neurons, not single action potentials. Synchronized activity produces slow, high-amplitude waves; desynchronized activity produces fast, low-amplitude waves.
On the MCAT: Questions link wave patterns to states of consciousness. Alert and awake: beta waves. Relaxed with eyes closed: alpha waves. Stage 1 sleep: theta waves. Stage 2: theta background with sleep spindles and K-complexes. Stage 3 (slow-wave sleep): delta waves, the slowest and largest. REM sleep: fast, irregular waves that resemble waking. From waking to deep sleep, frequency falls and amplitude rises. EEG also appears in method comparisons: it has good temporal resolution (changes within milliseconds) but poor spatial resolution, while fMRI localizes activity better but follows changes more slowly.
Common confusion: REM is not slow-wave sleep. Its EEG looks like wakefulness, which is why REM is called paradoxical sleep. Also, an EEG does not show brain structure and cannot localize deep activity well; it mainly samples cortical activity near the electrodes.
Sources
- Myers' Psychology
- Biological Psychology
Written for the MCAT and checked before it was published. For study reference only. Spotted an error? Let us know.