Which method records electrical activity of the brain via scalp electrodes?

• A. Angiography
• B. PET Scan
• C. EEG
• D. MRI

Answer: (C)

Recording electrical activity of the brain via scalp electrodes is done with electroencephalography. This technique measures the summed electrical potentials produced by neurons, especially the synchronized activity of cortical pyramidal neurons, as signals pass through the skull and scalp. The resulting brain waves reflect different states: slow delta waves in deep sleep, theta in drowsiness or certain tasks, alpha during relaxed wakefulness with eyes closed, and beta or gamma during active thinking. EEG offers excellent temporal resolution, capturing changes on the millisecond scale, but has limited spatial resolution because the signals blur as they traverse head tissues. This stands in contrast to imaging methods like angiography (which visualizes blood vessels with contrast), PET scans (which map metabolic activity with radioactive tracers), and MRI (which images structure and, in functional forms, brain activity through magnetic signals). EEG's noninvasive nature and ability to track rapid changes over time make it especially useful for evaluating seizures, sleep disorders, and monitoring anesthesia.