Which test records the brain's electrical activity?

• A. Electroencephalography (EEG)
• B. Electromyography (EMG)
• C. Magnetic Resonance Imaging (MRI)
• D. Positron Emission Tomography (PET)

Answer: (A)

The main idea here is that EEG records the brain’s electrical activity. Electroencephalography uses electrodes placed on the scalp to pick up the small voltage changes generated by neuron firing in the brain. These signals are then spit out as brain waves, which change in frequency and amplitude depending on the state of consciousness, sleep, or neurological events. Because EEG measures electrical activity directly, it has excellent temporal resolution, capturing rapid changes on a millisecond scale. This makes it particularly useful for studying sleep stages, seizures, and other dynamic brain processes.

In contrast, electromyography measures electrical activity in muscles, so it can assess nerve or muscle function but not brain activity. MRI uses strong magnetic fields to create detailed images of brain structure, and functional MRI tracks blood flow changes to infer activity—not the electrical signals themselves. PET scans detect metabolic activity by using radioactive tracers, again providing a different kind of information than direct electrical recordings.