What does an Electroencephalogram (EEG) primarily measure?

An Electroencephalogram (EEG) primarily measures the electrical activity of the brain. This technique involves placing electrodes on the scalp, which detect and record the electrical impulses produced by the brain's neurons. The resultant data allows clinicians and researchers to observe brain activity in real-time, identify patterns associated with different states of consciousness, diagnose conditions such as epilepsy, sleep disorders, and other neurological issues, as well as monitor the effects of treatments.

The other options, while important in their own right, do not relate to what an EEG measures. For instance, measuring blood flow in the brain would involve techniques like functional MRI or PET scans, which capture metabolic functions rather than direct electrical activity. Eye movement is typically assessed through methods like electrooculography, which tracks electrical potentials based on eye position. Heart rate is monitored by devices such as ECGs or pulse oximeters, which measure cardiac electrical activity and blood flow but have no relevance to cerebral electrical impulses. Thus, the primary and defining function of an EEG is its ability to capture the brain's electrical activity.