Electroencephalography, or EEG, is a noninvasive method to record the brain’s electrical activity using electrodes placed on the scalp. It measures voltage fluctuations produced by large groups of neurons, especially in the cerebral cortex. EEG is widely used in both clinical practice and research because it offers excellent temporal resolution in the millisecond range, allowing scientists to follow brain processes as they unfold in real time.

In research, EEG helps investigate perception, attention, memory, language, decision making, and motor control. By averaging signals across many trials, researchers obtain event related potentials, which are characteristic waveforms time locked to sensory, cognitive, or motor events. These components, such as early sensory responses or later decision related waves, reveal how information is processed step by step in the brain.

Different frequency bands in EEG signals, like delta, theta, alpha, beta, and gamma, are linked to distinct brain states and functions. For example, alpha rhythms are prominent during relaxed wakefulness with eyes closed, while beta and gamma activity increase during active concentration and sensory processing. Changes in these rhythms help track mental workload, arousal, and cognitive engagement.

Clinically, EEG is essential in diagnosing and monitoring epilepsy, sleep disorders, coma, and encephalopathies. It can identify abnormal rhythmic discharges and characterize sleep stages. Advanced methods use dense electrode arrays, source localization techniques, and machine learning to infer where in the brain signals originate and to decode patterns related to specific mental states or intentions. As technology improves, EEG is increasingly used in brain computer interfaces and in monitoring brain function in real world environments.