International 10-20 System
F - Frontal C - Central T - Temporal P - Parietal O - Occipital Z - Mid-line
Fp - Frontal Polar L - Odd R - Even Mid-line to Lateral Numbers Increase; C1 medial to C3, C2 medial to C4
Prime / ' - 2-3mm posterior placement CP3 means 1/2 way in between proportional CPi - ipsilateral to site CPc - central lateral
The international 10-20 system is a internationally recognized measurement system that provides a uniform map to cover the entire of the surface of the scalp into regions that are measured into ratios of 10 to 20 percent recommended anatomical landmarks measurements that allows one to map the head with precision to determine electrode placement for stimulating and recording of neuroelectric potentials. Specific anatomical landmarks are identified and then approximations of 10 to 20 percent distances between the landmarks determine intervals of electrode placement. This allows for replication and modification to be consistent over time. It also allows for generation of lines The American Clinical Neurophysiology Society recommends a minimum of 21 electrodes in the International 10-20 system however approximatey 75 electrode sites at five anterior/posterior planesare mapped.
Odd numbered electrodes are placed on the left side of the head and even numbered electrodes are placed on the right side of the head. Specific letters designate the lobes and nomenclature of the brain: "F" is frontal, "C" is central, "T" is temporal, "P" is parietal, "O" is occipital, "Z" is midline or zero, "Fp" is frontal polar, "A" is auricular. A numbering system is used where odd numbers are placed on the left and even numbers are placed on the right which increase in value from midline to lateral; C1 is medial to C3 is medial to C5, C2 is medial to C4 is medial to C6.
flexible system can help localize abnormalities by further subdividing the distances asymmetrical reproducible electrode placement allowing for accurate examination and comparison of EEG 10 - 20 percent intervals.
Exact measurements are needed to precisely determine the placement of each recording electrode however, in the operating room, quick approximations and modified placement are often used using ones hands. Measurements that are best made with a flexible measuring tape are modified by visual and hand measured approximations.
EEG measurements are made in a sequence of five steps however the full gamut of electrode placement for intraoperative neuromonitoring is not as extensive and approximated.
The measurements refer to three bony landmarks of the skull: (1) the inion, or the bony protuberance in the middle of the back of the head or the projecting part of the occipital bone at the base of the skull or the nape of the neck or the external occipital protuberance, (2) the nasion, or the bridge of the nose directly under the forehead or the depression of the skull in between the eyes, and (3) the preauricular point, or the depression of bone in front of the ear canal.
Step 1: The distance between nasion and inion is measured along the midline. Along this line, the frontopolar point, Fp, is marked at 10% above the nasion. Frontal (Fz), central (Cz), parietal (Pz) and occipital (O) points are marked at intervals of 20% of the entire distance leaving 10% for the interval between O and inion. The midline points Fpz and Oz are used only for intermediate measurements but routinely receive no electrode.
For IOM electrodes are typically placed at FPz, Cz, CP3, CP4 and CS5 for Somatosensory Evoked Potentials, at C3, C4 for Motor Evoked Potentials and C3', C3 and C4', C4 for linked quadripolar stimulation. A1 & A2 are used for ABR and XXXXXXXXXX for 8 Channels of EEG.
Step 2: The distance between the two pre-auricular points across Cz is measured, Along this line, the transverse position for the central points C3 and C4 and the temporal points T3 and T4 are marked 20 and 40% respectively from the midline.
Cz is a midline electrode that is used for Somatosensory evoked potentials and C3 and C4 are used to be marked for tcMEP electrode placement
Step 4: The circumference of the head is measured from the occipital point (O) through the temporal points T3 and T4 and the frontopolar points Fp. The longitudinal measurement for Fp1 is located on the circumference, 5% of the total length of the circumference to the left of Fpz. The longitudinal measurements for F7, T3, T5, O1, O2, T6, T4, F8, Fp2 are at distances of 10% of the circumference.
Step 4: The longitudinal distance from Fp1 and Fp through C3 and C4 to O1 and O2 is measured on each side. The midpoints of these distances ive the longitudinal coordinates of C3 and C4. The midpoints between Fp1 and C3 on the left, and Fp2 and C4 on the right give the longitudinal coordinates for F3 and F4. the midpoints between C3 and O1 on the left, and C4 and O2 on the right give the longitudinal coordinates for P3 and P4.
Step 5: Measurements from F7 to F8 through Fz define the transverse coordinates for F3 midway between F3 and Fz and for F4 miday between Fz and F8; measurements from midway between T5 and Pz and for P4 midway between Pz and T6.
International Federation of Societies for Electroencephalograpy and Clinical Neurophysiology (IFSECN) recommended a specific system of electrode placement order standard conditions for use in all laboratories. This is the system now known as the international 10-20 system. Specific measurements from these bony landmarks are used to determine the placement of electrodes. From these anatomical landmarks, speific measurements are made, and then 10% to 20% of a specified distance is used as the electrode interval. This enables replication consistently over time and between laboratories. The American Clinical Neurophysiology Society (formerly the American Electroencephalographic Society) has recommended using a minimum of 21 electrodes in the international 10-20 system.
Odd numbered electrodes are placed on the left side of the head, and even numbered electrodes on the right side of the head. Specific letters designate the anatomical area: for example "F" means frontal.
In 1991, the American Electroencephalographic Society added nomenclature guidelines that designate specific identifications and locations of 75 electrode positions along five anterior-posterior planes, lateral to the mid-line of 11 specific sites. In addition, four coronal chains lie anterior and four posterior, to the chain of 13 electrode sites between the earlobe electrodes along the midline at the Cz electrodes. Several electrodes have different names in the 10-20 system and the extended nomenclature. The electrodes T3 and T4 in the 10-20 system are referred to as T7 and T8 in the expanded system and T5 and T6 are referred to as P7 and P8 under the new nomenclature.
CY's book
Notes
Internationally recognized map of the surface of the scalp separated into regions that can be measured with ratios of 10 and 20 percent,
Electrode Placement; fisch & spehlmann's EEG Primer
The International 10-20 system of electrode placement provides for uniform coverage of the entire scalp. It uses the distances between bony landmarks of the head to generate a system of lines which run across the head and intersect at intervals of 10 or 20% of their total length. Electrodes are placed at the intersections. The uses of the 10-20 system assures symmetrical, reproducible electrode placement and allows a more accurate comparison of EEGs from the same patient and from different patients, recorded in the same or different laboratories. The system is flexible: additional electrodes which may be needed to accurately localize an abnormality can be incorporated by further subdividing the distances between intersections using the nomenclature of the modified 10-20 system.
The standard set of electrodes for adults consists of 21 recording electrodes and one ground electrode; 22 electrodes. The recording electrodes are named with a letter and a subscript. The letter is an abbreviation of the underlaying region: prefrontal or frontopolar (Fp), frontal (F), central (C), parietal (P), occipital (O) and auricular (A). The subscript is either the letter z, indicating zero or midline sagittal placement, or a number, indicating lateral placement. Odd numbers refer to electrodes on the left, even numbers refer to electrodes on the right side of the head. The numbers increase with increasing distance from the anterior posterior midline of the head. The inferior frontal electrodes F7 & F8 are often called "anterior temporal" electrodes because they fairly fatithfully record activity from the anterior temporal area.
Exact measurements are needed to precisely determine the placement of each recording electrode. Measurements are best made with a metric measuring tape of cloth or plastic. A grease pencil is used to mark electrode locations and the intermediate measurements needed to determine them. The measurements refer to three bony landmarks of the skull: (1) the inion, or the bony protuberance in the middle of the back of the head, (2) the nasion, or the bridge of the nose directly under the forehead, and (3) the preauricular point, or the depression of bone in front of the ear canal. Measurements are made in a sequence of five steps. Although the older nomenclature of the 10-20 system is used in the following description, readers are encouraged to adopt the newer terminology of the modified 10-20 system in which T3 and T4 are renamed T7 and T8 and T5 and T6 are renamed P7 and P8.
Step 1: The distance between nasion and inoin is measured along the midline. Along this line, the frontopolar point, Fp, is marked at 10% above the nasion. Frontal (Fz), central (Cz), parietal (Pz) and occipital (O) points are marked at intervals of 20% of the entire distance leaving 10% for the interval between O and inion. The midline points Fpz and Oz are used only for intermediate measurements but routinely receive no electrode.
Step 2: The distance betwen the two preauricular points across Cz is meassured, Along this line, the transverse position for the central points C3 and C4 and the temporal points T3 and T4 are mareked 20 and 40% respectively from the midline.
Step 4: The circumferance of the head is measured from the occipital point (O) through the temporal points T3 and T4 and the frontopoar points Fp. The longitudinal measurement for Fp1 is located on the circumferance, 5% of the total lengt of the circumferance to the left of Fpz. The longitudinal measurements for F7, T3, T5, O1, O2, T6, T4, F8, Fp2 are at distances of 10% of the circumferance.
Step 4: The longitudinal distance from Fp1 and Fp throgh C3 and C4 to O1 and O2 is measured on each side. The midpoints of these distances ive the longitudinal coodinates of C3 and C4. The midpoints between Fp1 and C3 on the left, and Fp2 and C4 on the right give the longitudinal coordinates for F3 and F4. the midpoints between C3 and O1 on the left, and C4 and O2 on the right give the longitudinal coordinates for P3 and P4.
Step 5: Measurements from F7 to F8 through Fz define the transverse corrdinates for F3 midway between F3 and Fz and for F4 miday bewtween Fz and F8; measurments from midway betwen T5 and Pz and for P4 midway between Pz and T6.
electrodes placed at Fz, Cz. and Pz, at all lateral points designated above on or near both ears in positions called A1 and A2 or non the mandibular angles in positions called M1 and M2, and on the point chosen for the ground electrode usually in the middle of the head or over one of the mastoids. The use of a smaller number of electrodes in routine EEG is now considered substandard. If needed, additional electrodes may be placed midway between these recording electrodes. In some cases, scalp lesions, skull asymmetries or other abnoralities may make it impossible to place electrodes in the positions of the 10-20 system. In these cases, electrodes should be placed as closely as possible to these positions and as symemetrically as possible on the two sides using the modified 10-20 systme of plaement. The eviations from standar placement should be indicated in a diagram on the EEG record. Other electrode placements may be use for EEG recordings from smal infants and for monitoring of extraceerebral activity such as eye movments, heart beat, respiratiory or other movements
True anterior temporal electrodes. Because interictal epileptiform activity frequenaly emanates from the anterior temporal lobe, some laboratories occasionally use addtional electrode placements that are closer to the anterior temporal region than F7 and F8. Often these are pladed according to the recommendation by Silverman and are referred to as true anterior templral electrods. lthough these electrodes are often labeled as T1 and T1, Aaccording to the internation 10-20 system. T1 and T2 would be placed between F7 and T3, and F8 and T4 respectvely. The positions for so-called true anterior temporal electrodes are located by first finding and imaginary line between the external auditory canal and the lateral canthus of the eye. The point along that line ithat is anterior to the external audtory canal by 1/3 the distance of the total line is then located. The lelectrode is placed 1 cm directly above that point.
modified 10-20 system. The placement of additional electrodes to those routinely emplyed in the 10-20 system may be indicated to : 1 improve the localization of ictal or interictal epileptiform activyt 2 increase spatial resolution for special studies using computerized EEG signal analysis or 3 detect highly localized evoked potentials. Ther american clinical neurophysiology society has developed new guidelines for extedning the 1020 system of electroe placement. In order to create a logincal nomenclature, four electrodes, T3, T4, T5 and T6 have been renaved T7, T8, P7 and P8 respectively . The american Cinical Neurophysiology Society guidelnines that explain renaming of these electrodes and the placement of the addtiional electrodes have been reproduced in Appendix iI.
All 21 electrodes and lpacements recommednding by the internation federation of societies for EEG and clinical neurophysiology should be used. The 10-20 system is the only one officially recommended by the International Federation of Socieites for EEG and Clinical Neurophyisiology. It is the moset commonly used existing system and it should be used universally. The use of the term modified 10-20 system is undesairable when it means that head measurements ave not been made and placements have been estimated. In this case, the term estimated 10-20 placement is more appropriate.
Lobes are abbreviated:
F- Frontal
P - Parietal
T - Temporal
O - Occiptial
Left side is odd numbers, the right side is even numbers, midline is Z
Nasion is top of nose, Inion is the bump at the back of the head; Nasion to Inion is 35 cm/or approximately 13.75 inches
Left pre-auricular to right pre-auricular is also 35 cm/ or approximately 13.75 inches
10% is 3.5 cm or approximately 1.5 inches 20% is 7 cm or approximately 3 inches
1. start at the nasion, this is 0/reference point
2. measure 3.5cm/10% toward the inion, (3.5) mark (Fpz)
3. add 7cm/20% (10.5 cm), mark (Fz)
4. add 7cm/20% (17.5cm), mark (Cz)
5. add 7cm/20% (24.5cm), mark (Pz)
6. add 7cm/20% (31.5cm), mark (Oz)
7. add 3.5cm/10% (35cm/inion), mark
Beginning at left pre-auricular (tragus), make similar measurements, using the intersection at Cz
1. start at the left pre-auricular (left tragus), measure 3.5cm/10% toward the right pre-auricular, mark
2. add 7cm/20% (3.5 cm), mark (T3)
3. add 7cm/20% (10.5 cm), mark (C3)
4. add 7cm/20% (17.5 cm), mark (Cz) should intersect with the previous measurement
5. add 7cm/20% (24..5 cm), mark (C4)
6. add 7cm/20% (31.5 cm), mark (T4)
7. add 3.5cm/20% (35 cm), mark (right tragus)
Practically, in the operating room before a case there isn't enough time to pull out a measuring tape and clearly define these areas so we must visually approximate and make general measurements with our hands.
Fz can be placed above posterior to the forehead/frontalis muscle where the hairline typically is in most adults. Cz can be approximating the intersection of the midline of the nasion/nose and perpendicular bisection of the tragi. Convention dictates that CP3 and CP4 are used for placement for SEP electrodes but in all practicality we are trying to get into negative space so anywhere behind the approximation of the central sulcus should yield well defined SEPs. your fingers can identify the left and right posterior "corners" of the skull with certainty. C3 and C4 are adjacent to Cz and the homunculus must be kept in mind for which muscle groups must be activated; lower limbs toward the midline and upper limbs more laterally. with the advent of quadripolar stimulation, a buffer/pocket zone around the motor cortex makes this easier to recruit with these electrodes placed anteriorly and laterally by 1-2 cm to the C3/C4 electrodes. CS5 is placed where the inion is and a ground/reference electrode can be placed in the contralateral mastoid.
The bulk of electrodes for each case can be placed this way allowing one to monitor SEPs, MEPs and 2 channels of EEG with faithful resolution. In some circumstances (each patient's anatomy is different) electrodes can be repositioned to optimize recordings.
In certain cases, (carotid endarterectomies, craniotomies, etcetera) 8 channels of EEG are used which can also be approximated with a fair degree of certainty, using left and right hemispheres in bespoke fashion catered to each surgery. General channels that can be used are:
8 electrodes per side would be ideal for maximum resolution but for practicality, ten electrodes can be used total with five placed on each side.
Odd numbered electrodes are placed on the left side of the head and even numbered electrodes are placed on the right side of the head. Specific letters designate the lobes and nomenclature of the brain: "F" is frontal, "C" is central, "T" is temporal, "P" is parietal, "O" is occipital, "Z" is midline or zero, "Fp" is frontal polar, "A" is auricular. A numbering system is used where odd numbers are placed on the left and even numbers are placed on the right which increase in value from midline to lateral; C1 is medial to C3 is medial to C5, C2 is medial to C4 is medial to C6.
flexible system can help localize abnormalities by further subdividing the distances asymmetrical reproducible electrode placement allowing for accurate examination and comparison of EEG 10 - 20 percent intervals.
Exact measurements are needed to precisely determine the placement of each recording electrode however, in the operating room, quick approximations and modified placement are often used using ones hands. Measurements that are best made with a flexible measuring tape are modified by visual and hand measured approximations.
EEG measurements are made in a sequence of five steps however the full gamut of electrode placement for intraoperative neuromonitoring is not as extensive and approximated.
The measurements refer to three bony landmarks of the skull: (1) the inion, or the bony protuberance in the middle of the back of the head or the projecting part of the occipital bone at the base of the skull or the nape of the neck or the external occipital protuberance, (2) the nasion, or the bridge of the nose directly under the forehead or the depression of the skull in between the eyes, and (3) the preauricular point, or the depression of bone in front of the ear canal.
Step 1: The distance between nasion and inion is measured along the midline. Along this line, the frontopolar point, Fp, is marked at 10% above the nasion. Frontal (Fz), central (Cz), parietal (Pz) and occipital (O) points are marked at intervals of 20% of the entire distance leaving 10% for the interval between O and inion. The midline points Fpz and Oz are used only for intermediate measurements but routinely receive no electrode.
For IOM electrodes are typically placed at FPz, Cz, CP3, CP4 and CS5 for Somatosensory Evoked Potentials, at C3, C4 for Motor Evoked Potentials and C3', C3 and C4', C4 for linked quadripolar stimulation. A1 & A2 are used for ABR and XXXXXXXXXX for 8 Channels of EEG.
Step 2: The distance between the two pre-auricular points across Cz is measured, Along this line, the transverse position for the central points C3 and C4 and the temporal points T3 and T4 are marked 20 and 40% respectively from the midline.
Cz is a midline electrode that is used for Somatosensory evoked potentials and C3 and C4 are used to be marked for tcMEP electrode placement
Step 4: The circumference of the head is measured from the occipital point (O) through the temporal points T3 and T4 and the frontopolar points Fp. The longitudinal measurement for Fp1 is located on the circumference, 5% of the total length of the circumference to the left of Fpz. The longitudinal measurements for F7, T3, T5, O1, O2, T6, T4, F8, Fp2 are at distances of 10% of the circumference.
Step 4: The longitudinal distance from Fp1 and Fp through C3 and C4 to O1 and O2 is measured on each side. The midpoints of these distances ive the longitudinal coordinates of C3 and C4. The midpoints between Fp1 and C3 on the left, and Fp2 and C4 on the right give the longitudinal coordinates for F3 and F4. the midpoints between C3 and O1 on the left, and C4 and O2 on the right give the longitudinal coordinates for P3 and P4.
Step 5: Measurements from F7 to F8 through Fz define the transverse coordinates for F3 midway between F3 and Fz and for F4 miday between Fz and F8; measurements from midway between T5 and Pz and for P4 midway between Pz and T6.
International Federation of Societies for Electroencephalograpy and Clinical Neurophysiology (IFSECN) recommended a specific system of electrode placement order standard conditions for use in all laboratories. This is the system now known as the international 10-20 system. Specific measurements from these bony landmarks are used to determine the placement of electrodes. From these anatomical landmarks, speific measurements are made, and then 10% to 20% of a specified distance is used as the electrode interval. This enables replication consistently over time and between laboratories. The American Clinical Neurophysiology Society (formerly the American Electroencephalographic Society) has recommended using a minimum of 21 electrodes in the international 10-20 system.
Odd numbered electrodes are placed on the left side of the head, and even numbered electrodes on the right side of the head. Specific letters designate the anatomical area: for example "F" means frontal.
In 1991, the American Electroencephalographic Society added nomenclature guidelines that designate specific identifications and locations of 75 electrode positions along five anterior-posterior planes, lateral to the mid-line of 11 specific sites. In addition, four coronal chains lie anterior and four posterior, to the chain of 13 electrode sites between the earlobe electrodes along the midline at the Cz electrodes. Several electrodes have different names in the 10-20 system and the extended nomenclature. The electrodes T3 and T4 in the 10-20 system are referred to as T7 and T8 in the expanded system and T5 and T6 are referred to as P7 and P8 under the new nomenclature.
CY's book
Notes
Internationally recognized map of the surface of the scalp separated into regions that can be measured with ratios of 10 and 20 percent,
Electrode Placement; fisch & spehlmann's EEG Primer
The International 10-20 system of electrode placement provides for uniform coverage of the entire scalp. It uses the distances between bony landmarks of the head to generate a system of lines which run across the head and intersect at intervals of 10 or 20% of their total length. Electrodes are placed at the intersections. The uses of the 10-20 system assures symmetrical, reproducible electrode placement and allows a more accurate comparison of EEGs from the same patient and from different patients, recorded in the same or different laboratories. The system is flexible: additional electrodes which may be needed to accurately localize an abnormality can be incorporated by further subdividing the distances between intersections using the nomenclature of the modified 10-20 system.
The standard set of electrodes for adults consists of 21 recording electrodes and one ground electrode; 22 electrodes. The recording electrodes are named with a letter and a subscript. The letter is an abbreviation of the underlaying region: prefrontal or frontopolar (Fp), frontal (F), central (C), parietal (P), occipital (O) and auricular (A). The subscript is either the letter z, indicating zero or midline sagittal placement, or a number, indicating lateral placement. Odd numbers refer to electrodes on the left, even numbers refer to electrodes on the right side of the head. The numbers increase with increasing distance from the anterior posterior midline of the head. The inferior frontal electrodes F7 & F8 are often called "anterior temporal" electrodes because they fairly fatithfully record activity from the anterior temporal area.
Exact measurements are needed to precisely determine the placement of each recording electrode. Measurements are best made with a metric measuring tape of cloth or plastic. A grease pencil is used to mark electrode locations and the intermediate measurements needed to determine them. The measurements refer to three bony landmarks of the skull: (1) the inion, or the bony protuberance in the middle of the back of the head, (2) the nasion, or the bridge of the nose directly under the forehead, and (3) the preauricular point, or the depression of bone in front of the ear canal. Measurements are made in a sequence of five steps. Although the older nomenclature of the 10-20 system is used in the following description, readers are encouraged to adopt the newer terminology of the modified 10-20 system in which T3 and T4 are renamed T7 and T8 and T5 and T6 are renamed P7 and P8.
Step 1: The distance between nasion and inoin is measured along the midline. Along this line, the frontopolar point, Fp, is marked at 10% above the nasion. Frontal (Fz), central (Cz), parietal (Pz) and occipital (O) points are marked at intervals of 20% of the entire distance leaving 10% for the interval between O and inion. The midline points Fpz and Oz are used only for intermediate measurements but routinely receive no electrode.
Step 2: The distance betwen the two preauricular points across Cz is meassured, Along this line, the transverse position for the central points C3 and C4 and the temporal points T3 and T4 are mareked 20 and 40% respectively from the midline.
Step 4: The circumferance of the head is measured from the occipital point (O) through the temporal points T3 and T4 and the frontopoar points Fp. The longitudinal measurement for Fp1 is located on the circumferance, 5% of the total lengt of the circumferance to the left of Fpz. The longitudinal measurements for F7, T3, T5, O1, O2, T6, T4, F8, Fp2 are at distances of 10% of the circumferance.
Step 4: The longitudinal distance from Fp1 and Fp throgh C3 and C4 to O1 and O2 is measured on each side. The midpoints of these distances ive the longitudinal coodinates of C3 and C4. The midpoints between Fp1 and C3 on the left, and Fp2 and C4 on the right give the longitudinal coordinates for F3 and F4. the midpoints between C3 and O1 on the left, and C4 and O2 on the right give the longitudinal coordinates for P3 and P4.
Step 5: Measurements from F7 to F8 through Fz define the transverse corrdinates for F3 midway between F3 and Fz and for F4 miday bewtween Fz and F8; measurments from midway betwen T5 and Pz and for P4 midway between Pz and T6.
electrodes placed at Fz, Cz. and Pz, at all lateral points designated above on or near both ears in positions called A1 and A2 or non the mandibular angles in positions called M1 and M2, and on the point chosen for the ground electrode usually in the middle of the head or over one of the mastoids. The use of a smaller number of electrodes in routine EEG is now considered substandard. If needed, additional electrodes may be placed midway between these recording electrodes. In some cases, scalp lesions, skull asymmetries or other abnoralities may make it impossible to place electrodes in the positions of the 10-20 system. In these cases, electrodes should be placed as closely as possible to these positions and as symemetrically as possible on the two sides using the modified 10-20 systme of plaement. The eviations from standar placement should be indicated in a diagram on the EEG record. Other electrode placements may be use for EEG recordings from smal infants and for monitoring of extraceerebral activity such as eye movments, heart beat, respiratiory or other movements
True anterior temporal electrodes. Because interictal epileptiform activity frequenaly emanates from the anterior temporal lobe, some laboratories occasionally use addtional electrode placements that are closer to the anterior temporal region than F7 and F8. Often these are pladed according to the recommendation by Silverman and are referred to as true anterior templral electrods. lthough these electrodes are often labeled as T1 and T1, Aaccording to the internation 10-20 system. T1 and T2 would be placed between F7 and T3, and F8 and T4 respectvely. The positions for so-called true anterior temporal electrodes are located by first finding and imaginary line between the external auditory canal and the lateral canthus of the eye. The point along that line ithat is anterior to the external audtory canal by 1/3 the distance of the total line is then located. The lelectrode is placed 1 cm directly above that point.
modified 10-20 system. The placement of additional electrodes to those routinely emplyed in the 10-20 system may be indicated to : 1 improve the localization of ictal or interictal epileptiform activyt 2 increase spatial resolution for special studies using computerized EEG signal analysis or 3 detect highly localized evoked potentials. Ther american clinical neurophysiology society has developed new guidelines for extedning the 1020 system of electroe placement. In order to create a logincal nomenclature, four electrodes, T3, T4, T5 and T6 have been renaved T7, T8, P7 and P8 respectively . The american Cinical Neurophysiology Society guidelnines that explain renaming of these electrodes and the placement of the addtiional electrodes have been reproduced in Appendix iI.
All 21 electrodes and lpacements recommednding by the internation federation of societies for EEG and clinical neurophysiology should be used. The 10-20 system is the only one officially recommended by the International Federation of Socieites for EEG and Clinical Neurophyisiology. It is the moset commonly used existing system and it should be used universally. The use of the term modified 10-20 system is undesairable when it means that head measurements ave not been made and placements have been estimated. In this case, the term estimated 10-20 placement is more appropriate.
Lobes are abbreviated:
F- Frontal
P - Parietal
T - Temporal
O - Occiptial
Left side is odd numbers, the right side is even numbers, midline is Z
Nasion is top of nose, Inion is the bump at the back of the head; Nasion to Inion is 35 cm/or approximately 13.75 inches
Left pre-auricular to right pre-auricular is also 35 cm/ or approximately 13.75 inches
10% is 3.5 cm or approximately 1.5 inches 20% is 7 cm or approximately 3 inches
1. start at the nasion, this is 0/reference point
2. measure 3.5cm/10% toward the inion, (3.5) mark (Fpz)
3. add 7cm/20% (10.5 cm), mark (Fz)
4. add 7cm/20% (17.5cm), mark (Cz)
5. add 7cm/20% (24.5cm), mark (Pz)
6. add 7cm/20% (31.5cm), mark (Oz)
7. add 3.5cm/10% (35cm/inion), mark
Beginning at left pre-auricular (tragus), make similar measurements, using the intersection at Cz
1. start at the left pre-auricular (left tragus), measure 3.5cm/10% toward the right pre-auricular, mark
2. add 7cm/20% (3.5 cm), mark (T3)
3. add 7cm/20% (10.5 cm), mark (C3)
4. add 7cm/20% (17.5 cm), mark (Cz) should intersect with the previous measurement
5. add 7cm/20% (24..5 cm), mark (C4)
6. add 7cm/20% (31.5 cm), mark (T4)
7. add 3.5cm/20% (35 cm), mark (right tragus)
Practically, in the operating room before a case there isn't enough time to pull out a measuring tape and clearly define these areas so we must visually approximate and make general measurements with our hands.
Fz can be placed above posterior to the forehead/frontalis muscle where the hairline typically is in most adults. Cz can be approximating the intersection of the midline of the nasion/nose and perpendicular bisection of the tragi. Convention dictates that CP3 and CP4 are used for placement for SEP electrodes but in all practicality we are trying to get into negative space so anywhere behind the approximation of the central sulcus should yield well defined SEPs. your fingers can identify the left and right posterior "corners" of the skull with certainty. C3 and C4 are adjacent to Cz and the homunculus must be kept in mind for which muscle groups must be activated; lower limbs toward the midline and upper limbs more laterally. with the advent of quadripolar stimulation, a buffer/pocket zone around the motor cortex makes this easier to recruit with these electrodes placed anteriorly and laterally by 1-2 cm to the C3/C4 electrodes. CS5 is placed where the inion is and a ground/reference electrode can be placed in the contralateral mastoid.
The bulk of electrodes for each case can be placed this way allowing one to monitor SEPs, MEPs and 2 channels of EEG with faithful resolution. In some circumstances (each patient's anatomy is different) electrodes can be repositioned to optimize recordings.
In certain cases, (carotid endarterectomies, craniotomies, etcetera) 8 channels of EEG are used which can also be approximated with a fair degree of certainty, using left and right hemispheres in bespoke fashion catered to each surgery. General channels that can be used are:
8 electrodes per side would be ideal for maximum resolution but for practicality, ten electrodes can be used total with five placed on each side.
*Animation showing how lines/grid is determined and how one can visually discern how the grid is created
Placement of recording electrodes. (a) Electrode names and placements in the international 10-20 system. (b-f) Steps in determining electrode placement as described in the text. (F&S)
10-20 Runoff
Head & Neck
10-20 System for Placement of Head Electrodes for EEG, MEP, SEP, EMG
Frontalis
Temporalis
Parietal
Occipital
Trigeminal Nerve
Facial Nerve
Platysma
Mastoid
Sternocleidomastoid
Spinal Accessory CN XI
Vagus Nerve
Cranial Nerves
I - Olfactory
II - Optic
III - Oculomotor
IV - Trochlear
V - Trigeminal
VI - Abducens
VII - Facial Nerve
VIII - Auditory Nerve
IX - Glossopharyngial
X - Vestibulocochlear
XI - Spinal Accessory
XII - Hypoglossal
Although the older nomenclature of the 10-20 system is used in the following description, readers are encouraged to adopt the newer terminology of the modified 10-20 system in which T3 and T4 are renamed T7 and T8 and T5 and T6 are renamed P7 and P8.
Head & Neck
10-20 System for Placement of Head Electrodes for EEG, MEP, SEP, EMG
Frontalis
Temporalis
Parietal
Occipital
Trigeminal Nerve
Facial Nerve
Platysma
Mastoid
Sternocleidomastoid
Spinal Accessory CN XI
Vagus Nerve
Cranial Nerves
I - Olfactory
II - Optic
III - Oculomotor
IV - Trochlear
V - Trigeminal
VI - Abducens
VII - Facial Nerve
VIII - Auditory Nerve
IX - Glossopharyngial
X - Vestibulocochlear
XI - Spinal Accessory
XII - Hypoglossal
Although the older nomenclature of the 10-20 system is used in the following description, readers are encouraged to adopt the newer terminology of the modified 10-20 system in which T3 and T4 are renamed T7 and T8 and T5 and T6 are renamed P7 and P8.