Electroencephalography

Electroencephalography is the neurophysiologic exploration of the electrical activity of the brain by the application of electrodes to the scalp. The resulting traces are known as an electroencephalogram (EEG) and represent so-called brain waves. This device is used to assess brain damage, epilepsy and other problems, such as brain death. EEG can also be used in conjunction with other types of brain imaging.

Neuroscientists and biological psychiatrists use EEGs to study the function of the brain by recording brain waves during controlled behavior of human volunteers and animals in lab experiments. Theories to explain sleep often rely on EEG patterns recorded during sleep sessions. In addition, the procedure is used clinically to assist in the diagnosis of epilepsy.

Contents

1 Methods 2 Wave types 3 Training the brain 3.1 Rhythmic stimuli 3.2 Neurofeedback 4 History 5 Notes 6 See also 7 External links

Methods

The recording is obtained by placing electrodes on the scalp, usually after preparing the scalp area by light abrasion and application of a conductive gel to reduce impedance. Each electrode is connected to an input of a differential amplifier (one amplifier per pair of electrodes), which amplifies the voltage between them (typically 1,000–100,000 times, or 60–100 dB of voltage gain), and then displays it on a screen or inputs it to a computer. The amplitude of the EEG is about 100 µV when measured on the scalp, and about 1-2 mV when measured on the surface of the brain.

The electrode-amplifier relationships are typically arranged in one of three ways:

Common reference derivation 

One terminal of each amplifier is connected to the same electrode, and all other electrodes are measured relative to this single point. It is typical to use a reference electrode placed somewhere along the scalp midline, or a reference that links both earlobe electrodes.

Average reference derivation 

The outputs of all of the amplifiers are summed and averaged, and this averaged signal is used as the common reference for each amplifier.

Bipolar derivation 

The electrodes are connected in series to an equal number of amplifiers. For example, amplifier 1 measures the difference between electrodes A and B, amplifier 2 measures the difference between B and C, and so on.

Wave types

Historically four major types of continuous rhythmic sinusoidal EEG waves are recognized (alpha, beta, delta and theta). There is no precise agreement on the frequency ranges for each type.

• Alpha (Berger's wave) is the frequency range from 8.5 Hz to 12 Hz. It is characteristic of a relaxed, alert state of consciousness and is present by the age of two years. Alpha rhythms are best detected with the eyes closed. Alpha attenuates with drowsiness and open eyes, and is best seen over the occipital (visual) cortex. An alpha-like normal variant called mu is sometimes seen over the motor cortex (central scalp) and attenuates with movement, or rather with the intention to move.
• Beta is the frequency range above 12 Hz. Disorganized, low amplitude beta is often associated with active, busy or anxious thinking and active concentration. Rhythmic beta is associated with various pathologies and drug effects.
• Delta is the frequency range up to 4 Hz and is often associated with the very young and certain encephalopathies and underlying lesions. It is seen in deep sleep.
• Gamma is the frequency range above 40 Hz (approximately 30-80 Hz to be precise). Gamma rhythms appear to be involved in higher mental activity, including perception and consciousness. It seems to be associated with consciousness, e.g. it disappears with general anesthesia. ^[1][2]
• Theta is the frequency range from 4.5 Hz to 8 Hz and is associated with drowsiness, childhood, adolescence and young adulthood. This EEG frequency can sometimes be produced by hyperventilation. Theta waves can be seen during hypnagogic states such as trances, hypnosis, deep day dreams, lucid dreaming and light sleep and the preconscious state just upon waking, and just before falling asleep. Controlled meditation or yogic meditation and/or breathing also produces theta waves. Mystics and Yogis are said to remain conscious and in control at this and at the Delta state.
• sensorimotor rhythm (SMR) is a middle frequency (about 12-16Hz) associated with physical stillness and body presence. SMR-Beta or SMR/LoBeta neurofeedback training is used to address the symptomatology and possible mechanisms of ADHD and epilepsy. ^[3][4]

Rhythmic slow activity in wakefulness is common in young children, but is abnormal in adults. In addition to the above types of rhythmic activity, individual transient waveforms such as sharp waves, spikes, spike-and-wave complexes occur in epilepsy, and other types of transients occur during sleep.

In the transition from wakefulness, through Stage I sleep (drowsiness), Stage II (light) sleep, to Stage III and IV (deep) sleep, first the alpha becomes intermittent and attenuated, then disappears. Stage II sleep is marked by brief bursts of highly rhythmic beta activity (sleep spindles) and K complexes (transient slow waves associated with spindles, often triggered by an auditory stimulus). Stage III and IV are characterized by slow wave activity. After a period of deep sleep, the sleeper cycles back to stage II sleep and/or rapid eye movement (REM) sleep, associated with dreaming. These cycles may occur many times during the night.

EEG under general anesthesia depends on the type of anesthetic employed. With halogenated anesthetics and intravenous agents such as propofol, a rapid (alpha or low beta), nonreactive EEG pattern is seen over most of the scalp, especially anteriorly; in some older terminology this was known as a WAR (widespread anterior rapid) pattern, contrasted with a WAIS (widespread slow) pattern associated with high doses of opiates.

Training the brain

There is some debate over whether one can entrain one’s own brain to achieve a specific brainwave frequency by using various techniques including sound stimuli and neurofeedback. According to brain training companies, altering the brain's electrical activity can be useful for lucid dreaming, encouraging alertness, astral projection, balancing the cerebral hemispheres, or simply in order to relax. On the other hand, there is considerable evidence that abnormal EEG patterns are significantly associated with functional problems^[5]. Clinical neurofeedback generally focusses on remediating those problems by normalizing the EEG; the result is sometimes improved function. One line of research concludes that there is no evidence to indicate that alpha or theta state is beneficial in any way, including for the purposes of thinking, balancing mental activity relaxation, or creativity. Sala et al^[6] suggest that brainwave training is based on mind myths and hype for the sale of expensive brainwave machines. This compilation of published research in addition to other systematic and coordinated research^[7] indicates that neurofeedback is generally not consistently effective, although certain mental and physical activities are associated with certain brain waves (eg, closing the eyes tends to result in a higher perportion of alpha rythms). Brain function is highly complex and specific to various locations within the brain, so general entrainment to a single frequency or state will always be unsatisfactory. Indeed, there have been successful legal action concerning companies who claim that brain training machines will increase IQ, extrasensory abilities, and learning^[8].

Rhythmic stimuli

One method proposed for attempting to entrain EEG rhythms is through sensory prompting. Medical EEG testing commonly includes intense light stimulation at various frequencies (to test for seizures). It has been suggested that indigenous peoples for centuries have used drumming to enter specific states and that these may be beneficial in some way. Some research indicates that computer programs or hardware that generate various frequencies are able to stimulate the brain and alter the brain's frequency via a much more gentle audio or visual stimulus^[9]. Other research counters these claims^[10]. Probably the best summary at this time is that entrainment, or "following" does occur in many but not all individuals, and that the result may have a transitory influence on the dominant subjective state reported by that person. There is some small-group study research to suggest that light-sound stimulation is clinically useful^[11], however, this will not always induce relaxation, and no evidence of paranormal activity has ever been found.

For example, if a person is in beta stage (purportedly highly alert) and an auditory stimulus of 10 Hz is applied to his or her brain for some time, the brain frequency is supposed to change towards the applied stimulus. It is claimed that the effect will be relaxing to the person. This phenomenon has been referred to as the frequency following response. This process is purported to work more efficiently if the stimulus applied to the brain begins at the brain's current frequency, then sweeps to the desired frequency. This will not be the case in all individuals.

Audio, binaural beat frequencies has also been suggested as a method by mind machine manufacturers, since the ears cannot hear sounds low enough to be useful for brain stimulation. They claim that if the left ear is presented with a steady tone of 500 Hz (21 cents sharp of B4) and the right ear a steady tone of 510 Hz (44 cents flat of C5), these two tones will combine in the brain. It is claimed that the difference, 10 Hz, is perceived by the brain and is an effective stimulus for brainwave entrainment.

Neurofeedback

Another method for possibly entraining the mind, or training for improved function, is through neurofeedback, a process in which the subject is given real-time biofeedback of their EEG rhythms. This technique has been proposed for the treatment of epilepsy, attention deficit disorder(ADHD), and other diseases and disorders. Some research has suggested that the operant conditioning of EEG ("neurofeedback") may produce lasting positive functional changes with a limited number of cases and individuals (For a current bibloigraphy see www.isnr.org/nfbarch/nbiblio.htm.) However, many ADHD researchers, most notably Russell Barkley, state that it is not true. Barkley claims that there is no evidence that neurofeedback works in any way. He, and the neurology research community, maintain that the supporting research is sloppy and, to date, has not managed to successfully prove anything.

History

Richard Caton (1842–1926), a physician practicing in Liverpool, presented his findings about electrical phenomena of the exposed cerebral hemispheres of rabbits and monkeys in 1875.

German physiologist Hans Berger (1873–1941) began his studies of the human EEG in 1920. He gave the device its name and is sometimes credited with inventing the EEG, though others had performed similar experiments. His work was later expanded by Edgar Douglas Adrian.

In the 1950s, English physician Walter Grey Walter developed an adjunct to EEG called EEG topography which allowed for the mapping of electrical activity across the surface of the brain. This enjoyed a brief period of popularity in the 1980's and seemed especially promising for psychiatry. It was never accepted by neurologists and remains a primarily a research tool up to now.

Three professional societies in the USA and several in Europe and elsewhere include in their charter or are devoted to the scientific exploration of EEG research. They are the International Society for Neuronal Regulation (http://www.isnr.org), the Association for Applied Psychophysiology and Biofeedback (http://www.aapb.org), and the Electrophysiology and Clinical Neuroscience Society (http://www.ecnsweb.com). Their focus is mainly on the effects of various conditions on the formation of brainwaves, as there is still no conclusive evidence suggesting that actual brainwave training has any lasting benefits at all.

Notes

1. http://brain.web-us.com Brain Waves ("40Hz") Research.
2. ^  Entrez PubMed Abstract Are neocortical gamma waves related to consciousness? Vanderwolf CH. Brain Research, 14 Feb. 2000, 855(2):217-24.
3. ^  WashingtonPost.com Meditation Gives Brain a Charge, Study Finds
4. ^  EEG Spectrum International Efficacy of SMR-Beta Neurofeedback for Attentional Processes, David A. Kaiser and Siegfried Othmer.
5. ^  EEG Research EEG Training for ADHD and Learning Disorders, Othmer, S & Othmer, S.F.
6. ^  Hughes JR, John ER. Conventional and quantitative electroencephalography in psychiatry. J Neuropsychiatry Clin Neurosci 1999;11:190-208. PMID 10333991.
7. ^  Sala, Sergio Della, editor. 1999. Mind myths: Exploring popular assumptions about the mind and brain. J. Wiley & Sons, New York. ISBN 0471983039
8. ^  International Society for Neuronal Regulation Comprehensive Neurofeedback Bibliography, D. Corydon Hammond.
9. ^  Federal Trade Commission Compaint In the Matter of ZYGON INTERNATIONAL, INC., a corporation, and DANE SPOTTS, individually and as an officer of said corporation.
10. ^  Lane JD, Kasian SJ, Owens JE, Marsh GR. Binaural auditory beats affect vigilance performance and mood. Physiol Behav 1998;63:249-52. PMID 9423966.
11. ^  Le Scouarnec RP, Poirier RM, Owens JE, Gauthier J, Taylor AG, Foresman PA. Use of binaural beat tapes for treatment of anxiety: a pilot study of tape preference and outcomes. Altern Ther Health Med 2001;7:58-63. PMID 11191043.
12. ^  See for example this commercial site reporting university research.

See also

• Electroencephalophone
• Bioelectromagnetism
• Dreamachine

External links

• EEG Spectrum International, Inc. is a corporation whose pledge is to "promote the achievement of full human potential through brain-based self-regulation techniques, and to help evolve human consciousness through the exploration and development of advanced technologies for self-regulation, self-awareness and self-knowledge".[12]
• OpenEEG - An open source hardware and software project to enable hobbyists to build personal EEG machines for biofeedback.
• BioEra - A shareware digital signal processing toolbox that supports the analysis of real time bio-signals for any biofeedback device, and can run on Windows XP, Linux, Mac OS X, PDA Linux and possibly any other platform where Java is supported.
• BrainStorm - A shareware MATLAB software toolbox for electromagnetic functional brain imaging using EEG and Magnetoencephalography.
• Brainwave Generator - A shareware software program which produces binaural beat frequencies in order to entrain the brain into a specific state
• Curry - A commercial software package integrating EEG, MEG, MRI and fMRI for accurate functional brain imaging using realistic BEM volume conductor models.
• Introduction to EEG
• Pocket-Neurobics - A retail provider of personal neurofeedback hardware.
• Univ. Wisconsin Study on Tibetan monks in meditation practice, where scientists observed much greater activation of fast-moving and unusually powerful gamma waves in the monks over other subjects.