BME355 Lab Listing EEG
Top navigation banner.



Lab Outline


Learning more


Study the EEG and understand the associated signal analysis.



In order to get an electrical signal from the body, suitable electrodes, amplification and appropriate display are required. Electroencephalography (EEG) uses amplified signals from electrodes placed on the scalp to measure microvolt potentials which show patterns of electrical activity representing neural activity in the brain.

The EEG can determine the relative strengths and positions of electrical activity in different brain regions. Changes in electrical activity due to stimulus, task or condition can help in the understanding of associated brain function. The EEG can help diagnose seizure disorders (epilepsy), head injuries, brain tumors, encephalitis, some kinds of infections, metabolic disturbances, and sleep disorders. While the EEG allows high temporal resolution, the spatial resolution is much less than in functional brain imaging (fMRI, PET).

EEG reading involves the interpretation of wave forms by their frequency and also by the shape of the wave. Artifacts and normal variants must be distiguished from abnormalities. The frequencies of the EEG waves run from 0.5Hz to hundreds of Hz. EEG machines usually show frequencies of up to 26Hz. Waves are usually defined by their frequency and are divided on this basis into alpha, beta, gamma and delta waves.

Certain waves are recognizable by their shape such as spikes or slow waves; in other instances pair or groups of waves have typical appearences. Spikes imply synchronous neural firing, such as in seizures.


Artifacts are transitory disturbances in the signal caused by technical defects, usually due to, for example, electrode movement, loss of contact, muscle activity obscuring the EEG, movements of the head, scratching the scalp, and sweating (can cause unwanted shorting). There can also be 60Hz artifacts, EKG artifacts and pulse artifacts (caused by the periodic movement of an electrode due to a pulse).


Alpha waves are those between 8 and 13Hz. Alpha is usually best seen in the posterior regions of the head on each side, being higher in amplitude on the dominant side. It is brought out by closing the eyes and by relaxation, and diminished by eye opening or alerting by any mechanism (thinking, calculating). It is the major rhythm in normal relaxed adults.


Beta ('fast’) activity has a frequency of 14Hz and higher. It is usually seen on both sides in symmetrical distribution and is most evident frontally. It is accentuated by sedatives especially benzodiazepines and barbiturates. It may be absent or reduced in areas of cortical damage. It is a normal rhythm and is the dominant rhythm in subjects who are alert or anxious or who have their eyes open.


Theta ('slow’) activity has a frequency of 4 to 7 Hz. It is abnormal in awake adults but is normal in children (up to 13 years old) and in sleep. It may be associated with confusion, stupor or coma; the cause may be structural e.g. hydrocephalus, brain swelling (cerebral edema), or toxic/metabolic e.g. liver or kidney failure, drug overdose, low thyroid, etc.


Delta activity is 3 Hz or below. It tends to be the highest in amplitude. In infants under one year and in sleep (stages 3 and 4), it is normal and is the dominant rhythm. It may occur focally with subcortical lesions and in general distribution with diffuse lesions, metabolic encephalopathy, hydrocephalus or deep midline lesions. Typically, it is most prominent frontally in adults and posteriorly in children.


Brain waves were discovered by Hans Berger in Germany in the 1920's.

EEG Signal Averaging Background material

Bottom navigation banner.