The Introductory Guide to EEG (Electroencephalography)

6 min readMar 17, 2022

EEG Definition

EEG stands for “electroencephalography” which is an electrophysiological process to record the electrical activity of the brain. EEG measures changes in the electrical activity produced by the brain. Voltage changes come from ionic current within and between some brain cells called neurons. For more background on the science and history behind EEG, refer to the Emotiv Introductory Guide to EEG below:

Types of Brainwaves that EEG Measures

The electrodes of an EEG device capture electrical activity expressed in various EEG frequencies. Using an algorithm called a Fast Fourier Transform (FFT), these raw EEG signals can be identified as distinct waves with different frequencies. Frequency, which refers to the speed of the electrical oscillations, is measured in cycles per second — one Hertz (Hz) is equal to one cycle per second. Brainwaves are categorized by frequency into four main types: Beta, Alpha, Theta and Delta.

EEG Waves in modern brain visualizer time series graph

The following paragraphs discuss some of the functions associated with the four main brain frequencies. These functions have simply been found to be associated with different brain frequencies — there is no one-to-one linear correspondence between a frequency band and a given function of the brain.

Beta Waves (frequency range from 14 Hz to about 30 Hz)

Beta waves are most closely associated with being conscious or in an awake, attentive and alert state. Low-amplitude beta waves are associated with active concentration, or with a busy or anxious state of mind. Beta waves are also associated with motor decisions (suppression of movement and sensory feedback of motion). When measured by an EEG device, the signals are often referred to as EEG beta waves.

Alpha Waves (frequency range from 7 Hz to 13 Hz)

Alpha waves are often associated with a relaxed, calm and lucid state of mind. They can be found in the occipital lobe or the posterior regions of the brain. Alpha waves can be induced by closing one’s eyes and relaxing, and they are rarely present during intense cognitive processes like thinking, mental calculus and problem-solving. In most adults, alpha waves range in frequency from 9 to 11 Hz. When measured by an EEG device, these are often referred to as EEG alpha waves.

Theta Waves (frequency range from 4 Hz to 7 Hz)

Brain activity within a frequency range comprised between 4 and 7 Hz is referred to as theta activity. Theta rhythm detected in EEG measurement is often found in young adults, particularly over the temporal regions and during hyperventilation. In older individuals, theta activity with an amplitude greater than about 30 millivolts (mV) is seen less commonly, except during drowsiness. When measured by an EEG device, these are often referred to as EEG theta waves.

Delta Waves (frequency range up to 4 Hz)

Delta activity is predominantly found in infants. Delta waves are associated with deep stages of sleep in older subjects. Delta waves have been documented interictally (between seizures) in patients with absence seizures, which involve brief, sudden lapses in attention.

Delta waves are characterized by low-frequency (about 3 Hz), high amplitude waves. Delta rhythms can be present during wakefulness — they are responsive to eye-opening and may be enhanced by hyperventilation as well. When measured by an EEG device, these are often referred to as EEG delta waves.

EEG Testing Process

Preparing for an EEG Procedure

The best way to prepare for an EEG test is always to ask the test administrators for specific preparation instructions. These instructions can vary by use case — for example, EEG recordings for consumer research, academic research or performance and wellness may require subjects to be active instead of lying down.

Companies like EMOTIV have pioneered advances in EEG technology that make conducting, processing and interpreting tests faster and more convenient. EMOTIV’s mobile and wireless EEG headsets can be set up in less than five minutes, and they enable the participant to move freely instead of confining them to a testing facility.

In advance of an EEG test, its important to tell the professional administering the test — whether that’s a doctor, employer or researcher — about any regular medications you take. It’s recommended that you wash your hair the night before the procedure and leave it free of any products. Avoid drinking or eating any caffeine at least 8 hours before the test. If you have to sleep during the EEG procedure, you may be instructed to limit your sleep the night before to ensure your brain can relax properly during the test.

EEG Monitoring

You’ll feel no pain or discomfort during an EEG procedure. During a clinical EEG procedure, you’ll be lying on a bed or a reclining chair and instructed to close your eyes. An EEG technician measures your head and marks where to apply the leads.

When the test begins, the electrodes record your brainwaves and sends the activity to a recording machine. The EEG machine then converts the data into a wave pattern for interpretation. After the recording is finished, the technician will remove the electrodes from your scalp.

Routine EEG tests in scientific or clinical settings take 30–60 minutes to complete, including around 20 minutes for initial set-up time. EEG tests conducted for consumer, individual performance and workplace research can be shorter or longer in duration depending on the testing purposes. EMOTIV’s wireless EEG headsets support quicker set up for these use cases (less than five minutes).

There should be no recovery time needed after a procedure. If you’ve taken a medication that has caused drowsiness in order to sleep during the test, the test administrator may recommend waiting at the facility until the effects have worn off or have someone drive you home.

EEG test side effects are rare. The electrodes don’t produce any sensations; they only record brain activity. Persons with epilepsy may experience a seizure from stimuli such as flashing lights during the procedure. A seizure during an EEG test is nothing to be scared of — it can actually help doctors diagnose the type of epilepsy and tailor the treatment accordingly.

EEG Interpretation and Procedure Results

If you’ve been recommended to have an EEG test for clinical reasons, your test results will be interpreted by a doctor who specializes in the nervous system. The neurologist will study the recording for normal and abnormal brain patterns. Brain wave patterns are very recognizable by the characteristics of their waveforms. For example, a burst suppression pattern, which is often observed in patients with inactive brain states such as from coma or general anesthesia, will show brief spikes (the burst) alternating with periods of flatness (the suppression).

Different types of epilepsy are characterized by distinct EEG patterns. A spike-wave pattern — a generalized, symmetrical EEG pattern — is often observed during an absence seizure, where a person experiences a brief loss of consciousness. A partial focal seizure, in which seizure activity only affects one area of the brain, is characterized by a low-voltage, fast rhythm pattern that appears in the EEGs data channel associated with that area.

The neurologist then sends the EEG measurement back to the doctor who ordered the test. Your doctor may schedule an appointment to review the EEG images and discuss the results with you. Depending on your condition, you may be recommended to a service called EEG neurofeedback or biofeedback as a follow-up. For example, people looking to strengthen brainwave patterns associated with focus might engage in neurofeedback therapy for ADHD.

Biofeedback therapy helps subjects control involuntary bodily processes. A subject experiencing, for example, high blood pressure, can view their bodily measurements on a monitor that’s receiving data from electrodes on their skin. Monitoring this activity helps teach relaxation and mental exercises that can alleviate symptoms.

Similarly, Neurofeedback relies on EEG to train the brain to function better. During this training, the patient is hooked up to an EEG machine and is viewing their brain activity in action. This often resembles a type of video game where the patient is “playing” the game with their brain to control their brain activity. The patient tries to improve the brain frequencies associated with brain dysfunction, the same way an athlete works on a weak muscle. EEG neurofeedback is often recommended for conditions such as epilepsy, bipolar disorder, ADHD and autism. While it can help these disorders, it cannot cure them.

Note: This is just general information about EEG. EMOTIV products are intended to be used for research applications and personal use only. Our products are not sold as Medical Devices as defined in EU directive 93/42/EEC. Our products are not designed or intended to be used for diagnosis or treatment of disease.




EMOTIV is a neuroinformatics company advancing understanding of the human brain using electroencephalography (EEG).