Elektroenkefalografia

Elektroenkefalografia, commonly known as electroencefalografia (EEG), is a non-invasive method for recording the electrical activity of the brain by placing electrodes on the scalp or skull. It measures the summed electrical potentials arising from cortical neurons, providing very high temporal resolution but relatively limited spatial detail.

Recordings are obtained with an array of electrodes arranged according to systems such as the 10-20 convention. Electrodes are referenced to a common contact or to an average reference, and skin preparation with conductive gel or paste helps reduce impedance. Typical recordings include periods of rest with eyes closed and eyes open, sometimes complemented by provocative procedures such as hyperventilation or photic stimulation to evoke responses.

The data are displayed as waveforms across frequency bands: delta (>4 Hz), theta (4–7 Hz), alpha (8–13 Hz), beta (13–30 Hz), and gamma (>30 Hz). Normal patterns vary by age and state; for example, the alpha rhythm is often prominent in relaxed adults with eyes closed. Abnormal findings may include epileptiform discharges, spikes or sharp waves, slowing, or periodic patterns.

Applications encompass diagnosis and monitoring of epilepsy, assessment of coma and prognosis after brain injury, evaluation of sleep disorders, encephalopathies, and research. EEG can also be used to record event-related potentials (ERPs) that reflect cognitive processing in response to stimuli.

Limitations include limited spatial localization and vulnerability to artifacts from eye movements, muscle activity, or environmental noise. Safety is high, with minimal risk beyond rare skin irritation from electrode paste. The technique has a long history dating to early 20th century work, notably by Hans Berger in 1929, and continues to evolve with advanced signal processing and ambulatory monitoring.