Why do eeg test

Content on WhatAnswers is provided "as is" for informational purposes. While we strive for accuracy, we make no guarantees. Content is AI-assisted and should not be used as professional advice.

Last updated: April 8, 2026

Quick Answer: An EEG (electroencephalogram) test measures electrical activity in the brain using electrodes placed on the scalp, primarily to diagnose and monitor conditions like epilepsy, sleep disorders, and brain injuries. It was first developed in 1924 by German psychiatrist Hans Berger, who recorded the first human EEG. Modern EEGs can detect brain wave patterns at frequencies ranging from 0.5 to 100 Hz, with typical clinical use focusing on 0.5-30 Hz. EEGs are non-invasive, safe, and widely used, with over 10 million performed annually worldwide for neurological assessments.

Key Facts

First human EEG recorded in 1924 by Hans Berger
Detects brain wave frequencies from 0.5 to 100 Hz
Over 10 million EEG tests performed annually worldwide
Primary use: diagnosing epilepsy (detects seizures in 70-80% of cases)
Non-invasive procedure with electrodes placed on scalp

Overview

An electroencephalogram (EEG) is a diagnostic test that records electrical activity in the brain using small metal discs (electrodes) attached to the scalp. Developed by German psychiatrist Hans Berger in 1924, who published his findings in 1929, EEG revolutionized neurology by providing the first non-invasive method to study brain function. Berger discovered alpha waves (8-13 Hz) and beta waves (14-30 Hz), naming the technique "electroencephalogram." Historically, EEG gained prominence in the 1930s-1940s for epilepsy diagnosis and sleep research. Today, it remains essential in neurology, with standardized 10-20 electrode placement systems developed in 1958 ensuring consistent measurements. EEG has evolved from analog recordings to digital systems, enabling advanced analysis like quantitative EEG (qEEG) for brain mapping.

How It Works

EEG works by detecting voltage fluctuations from ionic currents within neurons. Electrodes (typically 16-256) are placed on the scalp according to the International 10-20 system, measuring potentials between 10-100 microvolts. The signals are amplified 1,000-100,000 times and filtered to remove artifacts (e.g., from eye movements). Brain waves are categorized by frequency: delta (0.5-4 Hz) in deep sleep, theta (4-8 Hz) in drowsiness, alpha (8-13 Hz) in relaxed states, beta (13-30 Hz) in active thinking, and gamma (30-100 Hz) in cognitive processing. During a test, patients may be asked to hyperventilate or view flashing lights to provoke abnormalities. Data is analyzed visually or computationally to identify patterns like spikes (epilepsy) or slow waves (brain injury), with recordings lasting 20 minutes to 24 hours for ambulatory monitoring.

Why It Matters

EEG is crucial for diagnosing and managing neurological disorders, impacting millions globally. It is the gold standard for epilepsy, detecting interictal spikes in 70-80% of patients and guiding treatment like medication or surgery. In sleep medicine, EEG identifies sleep stages and disorders like narcolepsy. It assesses brain function in comas, traumatic brain injuries, and encephalopathies, with continuous EEG monitoring in ICUs reducing mortality by detecting non-convulsive seizures. EEG also aids in research on cognition, brain-computer interfaces, and neurofeedback therapy. Its non-invasive, real-time nature makes it safer and more accessible than alternatives like fMRI, with costs around $200-$1,000 per test. By enabling early diagnosis and monitoring, EEG improves patient outcomes and advances neuroscience.