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 During (inpatient) attack monitoring, a patient's archetypal access medications may be withdrawn.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.
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.
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