Which device records the electrical activity of the brain using electrodes placed on the scalp?

The device that records the electrical activity of the brain using electrodes placed on the scalp is the electroencephalogram, commonly known as EEG. EEG is a non-invasive technique that directly measures the electrical impulses produced by brain cells through a series of electrodes attached to the scalp. This allows for the monitoring of brain wave patterns and is particularly valuable in diagnosing conditions such as epilepsy, sleep disorders, and other neurological issues.

In contrast, other devices mentioned serve different purposes. Magnetic Resonance Imaging (MRI) provides detailed images of brain structures using magnetic fields and radio waves but does not measure electrical activity. A Computed Tomography (CT) scan combines X-ray images to create cross-sectional views of the brain, focusing on structural details rather than electrical signals. Positron Emission Tomography (PET) involves the use of radioactive tracers to visualize metabolic processes in the brain, which is also unrelated to direct electrical measurement. Consequently, EEG stands out as the preferred method for capturing the brain's electrical activity.