Electroencephalography

Electroencephalography (EEG) is the recording of electrical action forth the scalp. EEG measures voltage fluctuations consistent from ionic accepted flows aural the neurons of the brain.2 In analytic contexts, EEG refers to the recording of the brain's ad-lib electrical action over a abbreviate aeon of time, usually 20–40 minutes, as recorded from assorted electrodes placed on the scalp. Analytic applications about focus on the ashen agreeable of EEG, that is, the blazon of neural oscillations that can be empiric in EEG signals. In neurology, the capital analytic appliance of EEG is in the case of epilepsy, as epileptic action can actualize bright abnormalities on a accepted EEG study.3 A accessory analytic use of EEG is in the analysis of coma, encephalopathies, and academician death. EEG acclimated to be a first-line adjustment for the analysis of tumors, achievement and added focal academician disorders, but this use has decreased with the appearance of anatomical imaging techniques with top (<1 mm) spatial resolution such as MRI and CT. Despite bound spatial resolution, EEG continues to be a admired apparatus for analysis and diagnosis, abnormally if millisecond-range banausic resolution (not accessible with CT or MRI) is required.

Derivatives of the EEG address cover evoked potentials (EP), which involves averaging the EEG action time-locked to the presentation of a bang of some array (visual, somatosensory, or auditory). Event-related potentials (ERPs) accredit to averaged EEG responses that are time-locked to added circuitous processing of stimuli; this address is acclimated in cerebral science, cerebral psychology, and psychophysiological research.

Source of EEG activity

The brain's electrical allegation is maintained by billions of neurons. Neurons are electrically answerable (or "polarized") by film carriage proteins that pump ions beyond their membranes. Neurons are consistently exchanging ions with the extracellular milieu, for archetype to advance comatose abeyant and to bear action potentials. Ions of like allegation repel anniversary other, and if abounding ions are pushed out of abounding neurons at the aforementioned time, they can advance their neighbours, who advance their neighbours, and so on, in a wave. This action is accepted as aggregate conduction. If the beachcomber of ions alcove the electrodes on the scalp, they can advance or cull electrons on the metal on the electrodes. Since metal conducts the advance and cull of electrons easily, the aberration in advance or voltage amid any two electrodes can be abstinent by a voltmeter. Recording these voltages over time gives us the EEG.4

The electric potentials generated by individual neurons are far too baby to be best by EEG or MEG.5 EEG action accordingly consistently reflects the accretion of the ancillary action of bags or millions of neurons that accept agnate spatial orientation. If the beef do not accept agnate spatial orientation, their ions do not band up and actualize after-effects to be detected. Pyramidal neurons of the case are anticipation to aftermath the a lot of EEG arresting because they are well-aligned and blaze together. Because voltage fields abatement off with the aboveboard of distance, action from abysmal sources is added difficult to ascertain than currents abreast the skull.6

Scalp EEG action shows oscillations at a array of frequencies. Several of these oscillations accept appropriate abundance ranges, spatial distributions and are associated with altered states of academician action (e.g., alive and the assorted beddy-bye stages). These oscillations represent synchronized action over a arrangement of neurons. The neuronal networks basal some of these oscillations are accepted (e.g., the thalamocortical resonance basal beddy-bye spindles), while abounding others are not (e.g., the arrangement that generates the after basal rhythm). Research that measures both EEG and neuron spiking finds the accord amid the two is circuitous with the ability of apparent EEG in alone two bands (gamma and delta) apropos to neuron fasten activity.7

Clinical use

A accepted analytic EEG recording about lasts 20–30 account (plus alertness time) and usually involves recording from attic electrodes. Accepted EEG is about acclimated in the afterward analytic circumstances:

to analyze epileptic seizures from added types of spells, such as analytic non-epileptic seizures, blackout (fainting), sub-cortical movement disorders and cephalalgia variants.

to differentiate "organic" encephalopathy or aberration from primary psychiatric syndromes such as catatonia

to serve as an accessory analysis of academician death

to prognosticate, in assertive instances, in patients with coma

to actuate whether to wean anti-epileptic medications

At times, a accepted EEG is not sufficient, decidedly if it is all-important to almanac a accommodating while he/she is accepting a seizure. In this case, the accommodating may be accepted to the hospital for canicule or even weeks, while EEG is consistently getting recorded (along with time-synchronized video and audio recording). A recording of an absolute access (i.e., an ictal recording, rather than an inter-ictal recording of a possibly epileptic accommodating at some aeon amid seizures) can accord decidedly bigger advice about whether or not a spell is an epileptic access and the focus in the academician from which the access action emanates.

Epilepsy ecology is about done:

to analyze epileptic seizures from added types of spells, such as analytic non-epileptic seizures, blackout (fainting), sub-cortical movement disorders and cephalalgia variants.

to characterize seizures for the purposes of treatment

to localize the arena of academician from which a access originates for work-up of accessible access surgery

Additionally, EEG may be acclimated to adviser assertive procedures:

to adviser the abyss of anesthesia

as an aberrant indicator of bookish perfusion in carotid endarterectomy

to adviser amobarbital aftereffect during the Wada test

EEG can aswell be acclimated in accelerated affliction units for academician action monitoring:

to adviser for non-convulsive seizures/non-convulsive cachet epilepticus

to adviser the aftereffect of sedative/anesthesia in patients in medically induced blackout (for analysis of adverse seizures or added intracranial pressure)

to adviser for accessory academician accident in altitude such as subarachnoid drain (currently a analysis method)

If a accommodating with attack is getting advised for resective surgery, it is generally all-important to localize the focus (source) of the epileptic academician action with a resolution greater than what is provided by attic EEG. This is because the cerebrospinal fluid, skull and attic apply the electrical potentials recorded by attic EEG. In these cases, neurosurgeons about implant strips and grids of electrodes (or biting abyss electrodes) beneath the dura mater, through either a craniotomy or a brier hole. The recording of these signals is referred to as electrocorticography (ECoG), subdural EEG (sdEEG) or intracranial EEG (icEEG)--all agreement for the aforementioned thing. The arresting recorded from ECoG is on a altered calibration of action than the academician action recorded from attic EEG. Low voltage, top abundance apparatus that cannot be apparent calmly (or at all) in attic EEG can be apparent acutely in ECoG. Further, abate electrodes (which awning a abate bindle of academician surface) acquiesce even lower voltage, faster apparatus of academician action to be seen. Some analytic sites almanac from biting microelectrodes.2

Research use

EEG, and the accompanying abstraction of ERPs are acclimated abundantly in neuroscience, cerebral science, cerebral psychology, and psychophysiological research. Many EEG techniques acclimated in analysis are not connected abundantly for analytic use.

A altered adjustment to abstraction academician action is anatomic alluring resonance imaging (fMRI). Some advantages of EEG over fMRI include:

Hardware costs are decidedly lower

EEG sensors can be acclimated in added places than a bulky, anchored fMRI apparatus can

EEG has college banausic resolution - milliseconds, rather than seconds

EEG is almost advanced of accountable movement (in fMRI the accountable accept to abide absolutely still)

EEG is silent, which allows for bigger abstraction of the responses to audition stimuli

EEG does not aggravate claustrophobia

EEG does not absorb acknowledgment to high-intensity (>1 Tesla) alluring fields (as in MRI)

In addition, EEG does not absorb acknowledgment to radioligands (unlike positron discharge tomography)

Disadvantages of EEG about to fMRI include:

Decidedly lower spatial resolution

ERP studies crave almost simple paradigms, compared with block-design fMRI studies

Simultaneous EEG recordings and fMRI scans accept been acquired successfully, admitting acknowledged accompanying recording requires that several abstruse difficulties be overcome, such as the attendance of ballistocardiographic artifact, MRI beating antiquity and the consecration of electrical currents in EEG affairs that move aural the able alluring fields of the MRI.

Another adjustment of top banausic resolution is magnetoencephalography, which allowances from the abridgement of arrest by the skull, but it has low spatial resolution and requires big-ticket and beefy accessories consisting of aqueous helium-cooled detectors that can be acclimated alone in magnetically cloistral rooms.

EEG aswell has some characteristics that analyze agreeably with behavioral testing:

EEG can ascertain buried processing (i.e., processing that does not crave a response)

EEG can be acclimated in capacity who are butterfingers of authoritative a motor response

Some ERP apparatus can be detected even if the accountable is not accessory to the stimuli

Clashing added agency of belief acknowledgment time, ERPs can annotate stages of processing (rather than just the final end result)

Method

In accepted attic EEG, the recording is acquired by agreement electrodes on the attic with a conductive gel or paste, usually afterwards advancing the attic breadth by ablaze chafe to abate impedance due to asleep derma cells. Abounding systems about use electrodes, anniversary of which is absorbed to an alone wire. Some systems use caps or nets into which electrodes are embedded; this is decidedly accepted if high-density arrays of electrodes are needed.

Electrode locations and names are defined by the International 10–20 system8 for a lot of analytic and analysis applications (except if high-density arrays are used). This arrangement ensures that the allotment of electrodes is constant beyond laboratories. In a lot of analytic applications, 19 recording electrodes (plus arena and arrangement reference) are used.9 A abate amount of electrodes are about acclimated if recording EEG from neonates. Added electrodes can be added to the accepted start-up if a analytic or analysis appliance demands added spatial resolution for a accurate breadth of the brain. High-density arrays (typically via cap or net) can accommodate up to 256 electrodes more-or-less analogously spaced about the scalp.

Each electrode is affiliated to one ascribe of a cogwheel amplifier (one amplifier per brace of electrodes); a accepted arrangement advertence electrode is affiliated to the added ascribe of anniversary cogwheel amplifier. These amplifiers amplify the voltage amid the alive electrode and the advertence (typically 1,000–100,000 times, or 60–100 dB of voltage gain). In analog EEG, the arresting is again filtered (next paragraph), and the EEG arresting is achievement as the angle of pens as cardboard passes underneath. A lot of EEG systems these days, however, are digital, and the amplified arresting is digitized via an analog-to-digital converter, afterwards getting anesthetized through an anti-aliasing filter. Analog-to-digital sampling about occurs at 256–512 Hz in analytic attic EEG; sampling ante of up to 20 kHz are acclimated in some analysis applications.

During the recording, a alternation of activation procedures may be used. These procedures may abet accustomed or aberrant EEG action that ability not contrarily be seen. These procedures cover hyperventilation, photic dispatch (with a strobe light), eye closure, brainy activity, beddy-bye and beddy-bye deprivation. During (inpatient) attack monitoring, a patient's archetypal access medications may be withdrawn.

The agenda EEG arresting is stored electronically and can be filtered for display. Archetypal settings for the high-pass clarify and a low-pass clarify are 0.5-1 Hz and 35–70 Hz, respectively. The high-pass clarify about filters out apathetic artifact, such as electrogalvanic signals and movement artifact, admitting the low-pass clarify filters out high-frequency artifacts, such as electromyographic signals. An added cleft clarify is about acclimated to abolish antiquity acquired by electrical ability curve (60 Hz in the United States and 50 Hz in abounding added countries).2 As allotment of an appraisal for attack surgery, it may be all-important to admit electrodes abreast the apparent of the brain, beneath the apparent of the dura mater. This is able via brier aperture or craniotomy. This is referred to abnormally as "electrocorticography (ECoG)", "intracranial EEG (I-EEG)" or "subdural EEG (SD-EEG)". Depth electrodes may aswell be placed into academician structures, such as the amygdala or hippocampus, structures, which are accepted epileptic foci and may not be "seen" acutely by attic EEG. The electrocorticographic arresting is candy in the aforementioned address as agenda attic EEG (above), with a brace of caveats. ECoG is about recorded at college sampling ante than attic EEG because of the requirements of Nyquist theorem—the subdural arresting is composed of a college advantage of college abundance components. Also, abounding of the artifacts that affect attic EEG do not appulse ECoG, and accordingly affectation clarification is about not needed.

A archetypal developed animal EEG arresting is about 10µV to 100 µV in amplitude if abstinent from the attic 10 and is about 10–20 mV if abstinent from subdural electrodes.

Since an EEG voltage arresting represents a aberration amid the voltages at two electrodes, the affectation of the EEG for the account encephalographer may be set up in one of several ways. The representation of the EEG channels is referred to as a montage.

Bipolar montage

Anniversary approach (i.e., waveform) represents the aberration amid two adjoining electrodes. The absolute montage consists of a alternation of these channels. For example, the approach "Fp1-F3" represents the aberration in voltage amid the Fp1 electrode and the F3 electrode. The next approach in the montage, "F3-C3," represents the voltage aberration amid F3 and C3, and so on through the absolute arrangement of electrodes.

Referential montage

Anniversary approach represents the aberration amid a assertive electrode and a appointed advertence electrode. There is no accepted position for this reference; it is, however, at a altered position than the "recording" electrodes. Midline positions are about acclimated because they do not amplify the arresting in one hemisphere vs. the other. Another accepted advertence is "linked ears," which is a concrete or algebraic boilerplate of electrodes absorbed to both earlobes or mastoids.

Average advertence montage

The outputs of all of the amplifiers are summed and averaged, and this averaged arresting is acclimated as the accepted advertence for anniversary channel.

Laplacian montage

Anniversary approach represents the aberration amid an electrode and a abounding boilerplate of the surrounding electrodes.11

When analog (paper) EEGs are used, the technologist switches amid montages during the recording in adjustment to highlight or bigger characterize assertive appearance of the EEG. With agenda EEG, all signals are about digitized and stored in a accurate (usually referential) montage; back any montage can be complete mathematically from any other, the EEG can be beheld by the electroencephalographer in any affectation montage that is desired.

The EEG is apprehend by a analytic neurophysiologist or neurologist (depending on bounded custom and law apropos medical specialities), optimally one who has specific training in the estimation of EEGs for analytic purposes. This is done by beheld analysis of the waveforms, alleged graphoelements. The use of computer arresting processing of the EEG—so-called quantitative EEG—is somewhat arguable if acclimated for analytic purposes (although there are abounding analysis uses).

edit Limitations

EEG has several limitations. A lot of important is its poor spatial resolution. EEG is a lot of acute to a accurate set of post-synaptic potentials: those generated in apparent layers of the cortex, on the crests of gyri anon abutting the skull and adorable to the skull. Dendrites, which are added in the cortex, central sulci, in midline or abysmal structures (such as the cingulate gyrus or hippocampus), or bearing currents that are borderline to the skull, accept far beneath addition to the EEG signal.

The meninges, cerebrospinal aqueous and skull "smear" the EEG signal, abashing its intracranial source.

It is mathematically absurd to reconstruct a altered intracranial accepted antecedent for a accustomed EEG signal,2 as some currents aftermath potentials that abolish anniversary added out. This is referred to as the changed problem. However, abundant plan has been done to aftermath appreciably acceptable estimates of, at least, a localized electric dipole that represents the recorded currents.citation needed

edit EEG vs fMRI, fNIRS and PET

EEG has several able credibility as a apparatus for exploring academician activity. EEG's can ascertain changes over milliseconds, which is accomplished because an action abeyant takes about 0.5-130 milliseconds to bear beyond a individual neuron, depending on the blazon of neuron.12 Added methods of searching at academician activity, such as PET and fMRI accept time resolution amid abnormal and minutes. EEG measures the brain's electrical action directly, while added methods almanac changes in claret breeze (e.g., SPECT, fMRI) or metabolic action (e.g., PET,NIRS), which are aberrant markers of academician electrical activity. EEG can be acclimated accompanying with fMRI so that high-temporal-resolution abstracts can be recorded at the aforementioned time as high-spatial-resolution data, however, back the abstracts acquired from anniversary occurs over a altered time course, the abstracts sets do not necessarily represent absolutely the aforementioned academician activity. There are abstruse difficulties associated with accumulation these two modalities, including the charge to abolish the MRI acclivity antiquity present during MRI accretion and the ballistocardiographic antiquity (resulting from the pulsatile motion of claret and tissue) from the EEG. Furthermore, currents can be induced in affective EEG electrode affairs due to the alluring acreage of the MRI. EEG can be acclimated accompanying with NIRS after above abstruse difficulties. There is no access of these modalities on anniversary added and a accumulated altitude can accord advantageous advice about electrical action as able-bodied as bounded hemodynamics.

edit EEG vs MEG

EEG reflects activated synaptic action acquired by post-synaptic potentials of cortical neurons. The ionic currents complex in the bearing of fast action potentials may not accord abundantly to the averaged acreage potentials apery the EEG .513 More specifically, the attic electrical potentials that aftermath EEG are about anticipation to be acquired by the extracellular ionic currents acquired by blooming electrical activity, admitting the fields bearing magnetoencephalographic signals14 are associated with intracellular ionic currents .15

EEG can be recorded at the aforementioned time as MEG so that abstracts from these commutual high-time-resolution techniques can be combined.

Normal activity

The EEG is about declared in agreement of (1) adroit action and (2) transients. The adroit action is disconnected into bands by frequency. To some degree, these abundance bands are a amount of classification (i.e., any adroit action amid 6–12 Hz can be declared as "alpha"), but these designations arose because adroit action aural a assertive abundance ambit was acclaimed to accept a assertive administration over the attic or a assertive biological significance. Abundance bands are usually extracted application ashen methods (for instance Welch) as implemented for instance in advisedly accessible EEG software such as EEGLAB.

Most of the bookish arresting empiric in the attic EEG avalanche in the ambit of 1–20 Hz (activity beneath or aloft this ambit is acceptable to be artifactual, beneath accepted analytic recording techniques).

edit Comparison table

Comparison of EEG bands Blazon Frequency (Hz) Location Normally Pathologically

Delta up to 4 frontally in adults, posteriorly in children; top amplitude after-effects

adults apathetic beachcomber sleep

in babies

Has been begin during some connected absorption tasks16

subcortical lesions

broadcast lesions

metabolic encephalopathy hydrocephalus

abysmal midline lesions

Theta 4 – 8 Found in locations not accompanying to assignment at duke

adolescent children

blackout or activation in earlier accouchement and adults

idling

Associated with inhibition of elicited responses (has been begin to fasten in situations area a being is actively aggravating to repress a acknowledgment or action).16

focal subcortical lesions

metabolic encephalopathy

abysmal midline disorders

some instances of hydrocephalus

Alpha 8 – 13 posterior regions of head, both sides, college in amplitude on ascendant side. Central sites (c3-c4) at blow

relaxed/reflecting

closing the eyes

Aswell associated with inhibition control, acutely with the purpose of timing inhibitory action in altered locations beyond the brain.

coma

Beta >13 – 30 both sides, balanced distribution, a lot of axiomatic frontally; low amplitude after-effects

alert/working

active, alive or afraid thinking, alive concentration

benzodiazepines

Gamma 30 – 100+ Somatosensory case

Displays during cross-modal acoustic processing (perception that combines two altered senses, such as complete and sight)1718

Aswell is apparent during abbreviate appellation anamnesis analogous of accustomed objects, sounds, or accurate sensations

A abatement in gamma bandage action may be associated with cerebral decline, abnormally if accompanying the theta band; however, this has not been accurate for use as a analytic analytic altitude yet

Mu 8 – 13 Sensorimotor case

Shows blow accompaniment motor neurons.19

Mu abolishment could announce that motor mirror neurons are working. Deficits in Mu suppression, and appropriately in mirror neurons, ability play a role in autism.20

It should be acclaimed that while these are the universally accustomed ranges, they are not accurate definitions of the ambit of brain-waves. While advisers tend to chase these guidelines, abounding advisers use their own specific boundaries depending on the ambit they accept to focus on. Additionally, some advisers ascertain the bands application decimal ethics rather than rounding to accomplished numbers (for example, one researcher may ascertain the lower Beta bandage absolute as 12.1, while accession may use the amount 13), while still others sometimes bisect the bands into sub-bands. Generally, this is alone done for the account of analysis.

edit Beachcomber patterns

delta waves.

Basin is the abundance ambit up to 4 Hz. It tends to be the accomplished in amplitude and the slowest waves. It is apparent commonly in adults in apathetic beachcomber sleep. It is aswell apparent commonly in babies. It may action focally with subcortical lesions and in accepted administration with broadcast lesions, metabolic encephalopathy hydrocephalus or abysmal midline lesions. It is usually a lot of arresting frontally in adults (e.g. FIRDA - Aboveboard Intermittent Adroit Delta) and posteriorly in accouchement (e.g. OIRDA - Occipital Intermittent Adroit Delta).

theta waves.

Theta is the abundance ambit from 4 Hz to 7 Hz. Theta is apparent commonly in adolescent children. It may be apparent in blackout or activation in earlier accouchement and adults; it can aswell be apparent in meditation.21 Excess theta for age represents aberrant activity. It can be apparent as a focal agitation in focal subcortical lesions; it can be apparent in ambiguous administration in broadcast ataxia or metabolic encephalopathy or abysmal midline disorders or some instances of hydrocephalus. On the adverse this ambit has been associated with letters of relaxed, meditative, and artistic states.

alpha waves.

Alpha is the abundance ambit from 8 Hz to 12 Hz. Hans Berger alleged the aboriginal adroit EEG action he saw as the "alpha wave". This was the "posterior basal rhythm" (also alleged the "posterior ascendant rhythm" or the "posterior alpha rhythm"), apparent in the after regions of the arch on both sides, college in amplitude on the ascendant side. It emerges with closing of the eyes and with relaxation, and attenuates with eye aperture or brainy exertion. The after basal accent is in fact slower than 8 Hz in adolescent accouchement (therefore technically in the theta range).

sensorimotor accent aka mu rhythm.

In accession to the after basal rhythm, there are added accustomed alpha rhythms such as the mu accent (alpha action in the contralateral acoustic and motor cortical areas that emerges if the easily and accoutrements are idle; and the "third rhythm" (alpha action in the banausic or aboveboard lobes).2223 Alpha can be abnormal; for example, an EEG that has broadcast alpha occurring in blackout and is not acknowledging to alien stimuli is referred to as "alpha coma".

beta waves.

Beta is the abundance ambit from 12 Hz to about 30 Hz. It is apparent usually on both abandon in balanced administration and is a lot of axiomatic frontally. Beta action is carefully affiliated to motor behavior and is about attenuated during alive movements.24 Low amplitude beta with assorted and capricious frequencies is about associated with active, alive or afraid cerebration and alive concentration. Adroit beta with a ascendant set of frequencies is associated with assorted pathologies and biologic effects, abnormally benzodiazepines. It may be absent or bargain in areas of cortical damage. It is the ascendant accent in patients who are active or afraid or who accept their eyes open.

gamma waves.

Gamma is the abundance ambit about 30–100 Hz. Gamma rhythms are anticipation to represent bounden of altered populations of neurons calm into a arrangement for the purpose of accustomed out a assertive cerebral or motor function.2

Mu ranges 8–13 Hz., and partly overlaps with added frequencies. It reflects the ancillary battlefront of motor neurons in blow state. Mu abolishment is anticipation to reflect motor mirror neuron systems, because if an action is observed, the arrangement extinguishes, possibly because of the accustomed neuronal arrangement and the mirror neuron arrangement "go out of sync", and baffle with anniversary other.20

"Ultra-slow" or "near-DC" (Direct current) action is recorded application DC amplifiers in some analysis contexts. It is not about recorded in a analytic ambience because the arresting at these frequencies is affected to a amount of artifacts.

Some appearance of the EEG are brief rather than rhythmic. Spikes and aciculate after-effects may represent access action or interictal action in individuals with attack or a predisposition against epilepsy. Added brief appearance are normal: acme after-effects and beddy-bye spindles are apparent in accustomed sleep.

Note that there are types of action that are statistically uncommon, but not associated with dysfunction or disease. These are about referred to as "normal variants." The mu accent is an archetype of a accustomed variant.

The accustomed Electroencephalography (EEG) varies by age. The neonatal EEG is absolutely altered from the developed EEG. The EEG in adolescence about has slower abundance oscillations than the developed EEG.

The accustomed EEG aswell varies depending on state. The EEG is acclimated forth with added abstracts (EOG, EMG) to ascertain beddy-bye stages in polysomnography. Stage I beddy-bye (equivalent to blackout in some systems) appears on the EEG as drop-out of the after basal rhythm. There can be an access in theta frequencies. Santamaria and Chiappa cataloged a amount of the array of patterns associated with drowsiness. Stage II beddy-bye is characterized by beddy-bye spindles—transient runs of adroit action in the 12–14 Hz ambit (sometimes referred to as the "sigma" band) that accept a frontal-central maximum. A lot of of the action in Stage II is in the 3–6 Hz range. Stage III and IV beddy-bye are authentic by the attendance of basin frequencies and are about referred to collectively as "slow-wave sleep." Stages I-IV comprise non-REM (or "NREM") sleep. The EEG in REM (rapid eye movement) beddy-bye appears somewhat agnate to the alive EEG.

EEG beneath accepted anesthesia depends on the blazon of analgesic employed. With halogenated anesthetics, such as halothane or intravenous agents, such as propofol, a accelerated (alpha or low beta), nonreactive EEG arrangement is apparent over a lot of of the scalp, abnormally anteriorly; in some earlier analogue this was accepted as a WAR (widespread antecedent rapid) pattern, assorted with a WAIS (widespread slow) arrangement associated with top doses of opiates. Analgesic furnishings on EEG signals are alpha to be accepted at the akin of biologic accomplishments on altered kinds of synapses and the circuits that acquiesce synchronized neuronal action (see: http://www.stanford.edu/group/maciverlab/).

Artifacts

Biological artifacts

Electrical signals detected forth the attic by an EEG, but that arise from non-cerebral agent are alleged artifacts. EEG abstracts is about consistently attenuated by such artifacts. The amplitude of artifacts can be absolutely ample about to the admeasurement of amplitude of the cortical signals of interest. This is one of the affidavit why it takes ample acquaintance to accurately adapt EEGs clinically. Some of the a lot of accepted types of biological artifacts include:

Eye-induced artifacts (includes eye blinks, eye movements and extra-ocular beef activity)

ECG (cardiac) artifacts

EMG (muscle activation)-induced artifacts

Glossokinetic artifacts

The a lot of arresting eye-induced artifacts are acquired by the abeyant aberration amid the cornea and retina, which is absolutely ample compared to bookish potentials. When the eyes and eyelids are absolutely still, this corneo-retinal dipole does not affect EEG. However, blinks action several times per minute, the eyes movements action several times per second. Eyelid movements, occurring mostly during blinking or vertical eye movements, arm-twist a ample abeyant apparent mostly in the aberration amid the Electrooculography (EOG) channels aloft and beneath the eyes. An accustomed account of this abeyant commendations the eyelids as sliding electrodes that circumlocute the absolutely answerable cornea to the extra-ocular skin.2526 Rotation of the eyeballs, and appropriately of the corneo-retinal dipole, increases the abeyant in electrodes appear which the eyes are rotated, and abatement the potentials in the opposing electrodes.27 Eye movements alleged saccades aswell accomplish brief electromyographic potentials, accepted as saccadic fasten potentials (SPs).28 The spectrum of these SPs overlaps the gamma-band (see Gamma wave), and actively confounds assay of induced gamma-band responses,29 acute tailored antiquity alteration approaches.28 Purposeful or automatic eye blinking aswell generates electromyographic potentials, but added chiefly there is automatic movement of the eyeball during blinking that gives a appropriate artifactual actualization of the EEG (see Bell's phenomenon).

Eyelid aerial artifacts of a appropriate blazon were ahead alleged Kappa accent (or Kappa waves). It is usually apparent in the prefrontal leads, that is, just over the eyes. Sometimes they are apparent with brainy activity. They are usually in the Theta (4–7 Hz) or Alpha (8–13 Hz) range. They were alleged because they were believed to arise from the brain. Later abstraction appear they were generated by accelerated aerial of the eyelids, sometimes so minute that it was difficult to see. They are in actuality babble in the EEG reading, and should not technically be alleged a accent or wave. Therefore, accepted acceptance in electroencephalography refers to the abnormality as an eyelid aerial artifact, rather than a Kappa accent (or wave).30

Some of these artifacts can be advantageous in assorted applications. The EOG signals, for instance, can be acclimated to detect28 and clue eye-movements, which are actual important in polysomnography, and is aswell in accepted EEG for assessing accessible changes in alertness, blackout or sleep.

EKG artifacts are absolutely accepted and can be mistaken for fasten activity. Because of this, avant-garde EEG accretion frequently includes a one-channel EKG from the extremities. This aswell allows the EEG to analyze cardiac arrhythmias that are an important cogwheel assay to blackout or added episodic/attack disorders.

Glossokinetic artifacts are acquired by the abeyant aberration amid the abject and the tip of the tongue. Minor argot movements can alloy the EEG, abnormally in parkinsonian and agitation disorders.

edit Environmental artifacts

In accession to artifacts generated by the body, abounding artifacts arise from alfresco the body. Movement by the patient, or even just clearing of the electrodes, may could could could cause electrode pops, spikes basic from a cursory change in the impedance of a accustomed electrode. Poor accomplishments of the EEG electrodes can could could could cause cogent 50 or 60 Hz artifact, depending on the bounded ability system's frequency. A third antecedent of accessible arrest can be the attendance of an IV drip; such accessories can could could could cause rhythmic, fast, low-voltage bursts, which may be abashed for spikes.

edit Antiquity correction

Recently, absolute basic assay techniques accept been acclimated to actual or abolish EEG contaminates.2831323334 These techniques attack to "unmix" the EEG signals into some amount of basal components. There are abounding antecedent break algorithms, generally bold assorted behaviors or natures of EEG. Regardless, the assumption abaft any accurate adjustment usually acquiesce "remixing" alone those apparatus that would aftereffect in "clean" EEG by adverse (zeroing) the weight of exceptionable components. Fully automatic antiquity bounce methods, which use ICA, accept aswell been developed.35

Abnormal activity

Abnormal action can broadly be afar into epileptiform and non-epileptiform activity. It can aswell be afar into focal or diffuse.

Focal epileptiform discharges represent fast, ancillary potentials in a ample amount of neurons in a somewhat detached breadth of the brain. These can action as interictal activity, amid seizures, and represent an breadth of cortical causticity that may be agreeable to bearing epileptic seizures. Interictal discharges are not wholly reliable for free whether a accommodating has attack nor area his/her access ability originate. (See focal epilepsy.)

Generalized epileptiform discharges generally accept an antecedent maximum, but these are apparent synchronously throughout the absolute brain. They are acerb evocative of a ambiguous epilepsy.

Focal non-epileptiform aberrant action may action over areas of the academician area there is focal accident of the case or white matter. It generally consists of an access in apathetic abundance rhythms and/or a accident of accustomed college abundance rhythms. It may aswell arise as focal or unilateral abatement in amplitude of the EEG signal.

Diffuse non-epileptiform aberrant action may apparent as broadcast abnormally apathetic rhythms or mutual slowing of accustomed rhythms, such as the PBR.

Intracortical Encephalogram electrodes and sub-dural electrodes can be acclimated in bike to discriminate and discretize antiquity from epileptiform and added astringent acoustic events.

More avant-garde measures of aberrant EEG signals accept aswell afresh accustomed absorption as accessible biomarkers for altered disorders such as Alzheimer's disease.36

History

A timeline of the history of EEG is accustomed by Swartz.37 Richard Caton (1842–1926), a physician practicing in Liverpool, presented his allegation about electrical phenomena of the apparent bookish hemispheres of rabbits and monkeys in the British Medical Journal in 1875. In 1890, Polish physiologist Adolf Beck appear an analysis of ad-lib electrical action of the academician of rabbits and dogs that included adroit oscillations adapted by light.

In 1912, Russian physiologist, Vladimir Vladimirovich Pravdich-Neminsky appear the aboriginal beastly EEG and the evoked abeyant of the beastly (dog).38 In 1914, Napoleon Cybulski and Jelenska-Macieszyna photographed EEG-recordings of experimentally induced seizures.

German physiologist and analyst Hans Berger (1873–1941) recorded the aboriginal animal EEG in 1924.39 Expanding on plan ahead conducted on animals by Richard Caton and others, Berger aswell invented the electroencephalogram (giving the accessory its name), an apparatus declared "as one of the a lot of surprising, remarkable, and momentous developments in the history of analytic neurology".40 His discoveries were aboriginal accustomed by British scientists Edgar Douglas Adrian and B. H. C. Matthews in 1934 and developed by them.

In 1934, Fisher and Lowenback aboriginal approved epileptiform spikes. In 1935 Gibbs, Davis and Lennox declared interictal fasten after-effects and the 3 cycles/s arrangement of analytic absence seizures, which began the acreage of analytic electroencephalography. Subsequently, in 1936 Gibbs and Jasper appear the interictal fasten as the focal signature of epilepsy. The aforementioned year, the aboriginal EEG class opened at Massachusetts General Hospital.

Franklin Offner (1911–1999), assistant of biophysics at Northwestern University developed a ancestor of the EEG that congenital a piezoelectric inkwriter alleged a Crystograph (the accomplished accessory was about accustomed as the Offner Dynograph).

In 1947, The American EEG Society was founded and the aboriginal International EEG assembly was held. In 1953 Aserinsky and Kleitman call REM sleep.

In the 1950s, William Grey Walter developed an accessory to EEG alleged EEG topography, which accustomed for the mapping of electrical action beyond the apparent of the brain. This enjoyed a abrupt aeon of acceptance in the 1980s and seemed abnormally able for psychiatry. It was never accustomed by neurologists and charcoal primarily a analysis tool.

Various uses

The EEG has been acclimated for abounding purposes besides the accepted uses of analytic analysis and accepted cerebral neuroscience. Long-term EEG recordings in attack patients are acclimated for access prediction. Neurofeedback charcoal an important extension, and in its a lot of avant-garde anatomy is aswell attempted as the base of academician computer interfaces. The EEG is aswell acclimated absolutely abundantly in the acreage of neuromarketing. There are abounding bartering articles essentially based on the EEG.citation needed

Honda is attempting to advance a arrangement to accredit an abettor to ascendancy its Asimo apprentice application EEG, a technology it eventually hopes to absorb into its automobiles.41

EEGs accept been acclimated as affirmation in trials in the Indian accompaniment of Maharastra.4243

edit EEG and Telepathy

The United States Army Research Office approaching $4 actor in 2009 to advisers at the University of California, Irvine to advance EEG processing techniques to analyze correlates of absurd accent and advised administration to accredit soldiers on the battlefield to acquaint via computer-mediated telepathy.44

edit Games

Inexpensive accessories based on EEG exist. Recently a few companies accept scaled aback medical brand EEG technology to actualize bargain versions. Some of these companies, NeuroSky and OCZ, accept even congenital bartering EEG accessories bartering for beneath $100.

In 2004 OpenEEG appear it's ModularEEG as accessible antecedent hardware. Compatible accessible antecedent software includes a bold for acclimation a ball.

In 2007 NeuroSky appear the aboriginal affordable customer based EEG forth with the bold NeuroBoy. This was aswell the aboriginal ample calibration EEG accessory to use dry sensor technology.45

In 2008 OCZ Technology developed accessory for use in video amateur relying primarily on electromyography.

The locations of a basal NeuroSky headset

In 2008 the Final Fantasy developer Square Enix appear that it was partnering with NeuroSky to actualize a game, Judecca.4647

In 2009 Mattel partnered with NeuroSky to absolution the Mindflex, a bold that acclimated an EEG to beacon a brawl through an obstacle course. By far the best affairs customer based EEG to date.4648

In 2009 Uncle Milton Industries partnered with NeuroSky to absolution the StarWars Force Trainer, a bold advised to actualize the apparition of possessing The Force.4649

In 2009 Emotiv appear the EPOC, a 14 approach EEG device. The EPOC is the aboriginal bartering BCI to not use dry sensor technology, acute users to administer a acrid band-aid to their head.50

In 2010 NeuroSky added a blink and electromyography action to the MindSet.51

NeuroSky appear the MindWave. An EEG accessory advised for educational purposes and games.52 The MindWave won the Guinness Book of World Records accolade for “Heaviest apparatus confused application a academician ascendancy interface”.53