What is Electroencephalography (EEG)

EEG provides evidence of brain functions.

Electroencephalography (EEG) measures electrical brain waves. Brain cells communicate by producing tiny electrical impulses. In an EEG, electrodes are placed on the scalp over multiple areas of the brain to detect and record patterns of electrical activity. Measuring brain activity has many applications ranging from clinical use to research and even games.

Setting up electrodes

Setting up EEG electrodes for research.

Widely used in diagnosing neurological disorders.

An EEG can tell us if there is abnormal electrical activity in the brain and, in some cases, the types of seizures you might be going through. One of the most common EEG applications is to show the type and location of the activity in the brain during a seizure. This information can then be used for making the right diagnosis.

Beside seizures, an EEG is also used to evaluate people who have problems associated with brain functions. Problmes like these might include, for example, coma, problems with memory, tumors, or weakness of specific body parts (such as weakness causedby a stroke). An EEG can also be used to determine brain death.

“Routine EEG”

So called routine EEG recording typically lasts 20–30 minutes. This usually involves recording from many scalp electrodes. Routine EEG is normally used in clinical circumstances where short measurement is sufficient (for example, distinguishing epilectic seizure from other types of seizures or to evaluate coma).

“Long term EEG”

Sometimes a routine EEG is not enough. This most often happens when there’s need to record a patient while she’s having a seizure. In these cases Long term EEG is being used. It means, the patient stays in hospital for several days, while EEG is constantly being recorded. Normally EEG is synchronized with video and audio. A recording of an actual seizure offers valuable information about whether or not there is an epileptic seizure. Long term EEG also shows the focus in the brain from where the seizure activity emanates. Long term EEG can also be used in hospitals to evaluate the depth of anesthesia.

EEG in research

EEG is widely used in cognitive science, neuroscience and psychophysiological research. Many EEG techniques used in research are not standardized sufficiently for clinical use, which is the main difference between research EEG and clinical EEG.

fMRI vs. EEG

A widely used method for studying brain functions is fMRI (functional Magnetic Resonance Imaging). fMRI measures changes in brain blood flow during specific tasks or stimulations. When comparing EEG to fMRI there are several advantages of EEG over fMRI:

  • EEG hardware costs significantly less than fMRI hardware
  • EEG is more portable than large fMRI machine
  • EEG has higher resolution (12.5 microseconds in NeurOne EEG vs. seconds in fMRI)
  • EEG doesn’t expose patients to high-intensity magnetic fields
  • EEG is silent, which is important when studying responses to audio.

Simultaneous EEG recordings and fMRI scans have been obtained successfully with the latest devices. However, successful simultaneous recording requires that several technical difficulties are taken into account, such as the presence of many artifacts.

EEG devices

EEG devices setup for measurement.

EEG also has some characteristics that make it recommended method on behavioral testing:

  • EEG can detect processing that does not require a response
  • EEG can be used in subjects who aren’t capable of making motor responses
  • Some ERP components can be detected even when the subject is not attending to the stimuli
  • Unlike other means of studying reaction time, ERPs can explicate stages of processing (rather than only the final end result).


  1. EEG on Discovery Health
  2. EEG on eMedicine Health

Recommended readings

  1. M. H. Libenson (2009); Practical Approach to Electroencephalography
  2. A. James Rowan (2003); Primer of EEG: With Mini-Atlas

Related products

  1. NeurOne EEG System
  2. Mega Innovation
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