|
|
The electrodes are placed on the scalp by an EEG technician according to internationally agreed-upon criteria. In order to locate the exact electrode position, this system uses four anatomical landmarks from which measurements can be made. The nasion is the indentation between the forehead and the nose, the inion is a ridge that can be felt at the midline of the back of the skull, over the occipital area, and the preauricular points are defined as the indentations just above the cartilage that covers the external ear openings. The electrode locations and distances between the electrodes are then defined as 10% or 20% of these anatomical distances. Occasionally, additional electrodes (sphenoidal and suboccipital, for instance) are placed to enhance the likelihood of detecting and determining the location of EEG waves that may be too small or too deep in the brain to be detected by routinely placed electrodes.
The names of the electrode sites use alphabetical abbreviations that identify the lobe or area of the brain to which each electrode refers:
F = frontal
Fp = frontopolar
T = temporal
C = central
P = parietal
O = occipital
A = auricular (ear electrode).
The localization of the brain waves within the brain regions or lobes is further narrowed by adding electrodes, which are given numbers such as T3, T4, P3, P4. Even numbers identify electrode positions on the right side of the head, and odd numbers refer to the left side. The label "z" points to electrode sites in the midline of the head. For example, Cz refers to the midline central region of the head.
Often an EKG (electrocardiogram), a record of the heartbeat, also appears on the EEG printout.
The EEG records brain waves from different amplifiers using various combinations of electrodes called montages. In bipolar montages, consecutive pairs of electrodes are linked by connecting the electrode input 2 of one channel to input 1 of the subsequent channel, so that adjacent channels have one electrode in common. The bipolar chains of electrodes may be connected going from front to back (longitudinal) or from left to right (transverse).
Another type of montage is the referential montage. In this type, various electrodes are connected to input 1 of each amplifier and a reference electrode is connected to input 2 of each amplifier. Ideally, inactive electrodes (ones that are uninvolved in the electrical field being studied) are chosen as references.
What does the doctor learn from looking at the EEG?Being able to locate the origin of electrical activity ("localization") is critical to being able to interpret the EEG tracings meaningfully. Localization of normal or abnormal brain waves in bipolar montages is usually accomplished by identifying "phase reversal," a deflection of the two channels within a chain pointing to opposite directions. (See sample.) In a referential montage, all channels may show deflections in the same direction. If the electrical activity at the active electrodes is positive when compared to the activity at the reference electrode, the deflection will be downward. Electrodes where the electrical activity is the same as at the reference electrode will not show any deflection. In general, the electrode with the largest upward deflection represents the maximum negative activity in a referential montage.
Topic Editor: Steven C. Schachter, M.D.
Last Reviewed: 12/15/06
This content is user-generated. Content is not monitored nor consistently reviewed by the epilepsy.com Editorial Board. Epilepsy.com therefore cannot guarantee the accuracy of any content edited with the Wiki sections. While epilepsy.com, the Epilepsy Therapy Project, and its partners encourage visitor interaction and publishing within these sections, users should use caution when exploring content, especially as it pertains to health concerns. No content on epilepsy.com is intended to replace the care of a doctor. We encourage you to contact your own health care provider for individual medical advice. We cannot provide second opinions or make specific recommendations regarding therapy, nor does this Wiki content constitute a recommendation for any diagnosis or treatment options.
The electrodes are placed on the scalp by an EEG technician according to internationally agreed-upon criteria. In order to locate the exact electrode position, this system uses four anatomical landmarks from which measurements can be made. The nasion is the indentation between the forehead and the nose, the inion is a ridge that can be felt at the midline of the back of the skull, over the occipital area, and the preauricular points are defined as the indentations just above the cartilage that covers the external ear openings. The electrode locations and distances between the electrodes are then defined as 10% or 20% of these anatomical distances. Occasionally, additional electrodes (sphenoidal and suboccipital, for instance) are placed to enhance the likelihood of detecting and determining the location of EEG waves that may be too small or too deep in the brain to be detected by routinely placed electrodes.
The names of the electrode sites use alphabetical abbreviations that identify the lobe or area of the brain to which each electrode refers:
F = frontal
Fp = frontopolar
T = temporal
C = central
P = parietal
O = occipital
A = auricular (ear electrode).
The localization of the brain waves within the brain regions or lobes is further narrowed by adding electrodes, which are given numbers such as T3, T4, P3, P4. Even numbers identify electrode positions on the right side of the head, and odd numbers refer to the left side. The label "z" points to electrode sites in the midline of the head. For example, Cz refers to the midline central region of the head.
Often an EKG (electrocardiogram), a record of the heartbeat, also appears on the EEG printout.
The EEG records brain waves from different amplifiers using various combinations of electrodes called montages. In bipolar montages, consecutive pairs of electrodes are linked by connecting the electrode input 2 of one channel to input 1 of the subsequent channel, so that adjacent channels have one electrode in common. The bipolar chains of electrodes may be connected going from front to back (longitudinal) or from left to right (transverse).
Another type of montage is the referential montage. In this type, various electrodes are connected to input 1 of each amplifier and a reference electrode is connected to input 2 of each amplifier. Ideally, inactive electrodes (ones that are uninvolved in the electrical field being studied) are chosen as references.
What does the doctor learn from looking at the EEG?Being able to locate the origin of electrical activity ("localization") is critical to being able to interpret the EEG tracings meaningfully. Localization of normal or abnormal brain waves in bipolar montages is usually accomplished by identifying "phase reversal," a deflection of the two channels within a chain pointing to opposite directions. (See sample.) In a referential montage, all channels may show deflections in the same direction. If the electrical activity at the active electrodes is positive when compared to the activity at the reference electrode, the deflection will be downward. Electrodes where the electrical activity is the same as at the reference electrode will not show any deflection. In general, the electrode with the largest upward deflection represents the maximum negative activity in a referential montage.
| Title | Posted | |
|---|---|---|
| Normal EEG but continuing seizures | Aug 13, 2009 | |
| Amazon | ||
| I had a seizure during my EEG lights did it! | Aug 7, 2009 | |
| paigeg | ||
| Is this Epilepsy? | Oct 6, 2009 | |
| Black.Pearl | ||
| Is it epilepsy or not? | Aug 5, 2009 | |
| Lovebug | ||
| EEG impression differs from docs notes | Oct 26, 2009 | |
| redb0ne | ||
| What if you spend a week in video EEG monitoring and can't record a seizure? | Aug 6, 2009 | |
| celee | ||
| I am afraid they will take me off my meds | Aug 5, 2009 | |
| Lovebug | ||
| What in the world is happening to me? | Sep 23, 2009 | |
| hlogan911 | ||
| Seizures vs. Fainting | Oct 1, 2009 | |
| JenLake | ||
| View all Forums | ||
| Title | Posted | |
|---|---|---|
| Have I had a seizure? Any of these symptoms familiar? | Feb 9, 2010 | |
| scotchyscotch | ||
| TLE or PNES? | Feb 9, 2010 | |
| mel239 | ||
| Can bacteria be related to seizures? | Feb 9, 2010 | |
| larryz | ||
| Simple Partial Seizures and EEG/EKG | Feb 9, 2010 | |
| erkadrka | ||
| NyQuil | Feb 9, 2010 | |
| Eilliem | ||
| Can taking OTC medications for cold, flu and sinus infections result in seizures? | Feb 9, 2010 | |
| larryz | ||
| twitchy arm | Feb 9, 2010 | |
| emzclarinet | ||
| How long do your symptoms last (if they ever even go away) | Feb 9, 2010 | |
| jasssmit | ||
| Who is your personal hero? | Feb 9, 2010 | |
| phylisfjohnson | ||
| Causes of Underemployment. | Feb 9, 2010 | |
| Matthew Simington | ||
| View all Forums | ||
| Title | Page Views | |
|---|---|---|
| my.epilepsy.com Updates | 20,442 | |
| epi_help | ||
| topamax and weight loss | 18,960 | |
| alexia mom | ||
| kepra | 18,900 | |
| brian mattingly | ||
| Possible cure for absence seizures | 15,799 | |
| pdl1 | ||
| Epilepsy and marijuana | 15,559 | |
| cjad234 | ||
| Sexual Side Effects | 13,109 | |
| George R | ||
| How exactly do aura's feel | 13,010 | |
| WendyBendy | ||
| MEDICAL ALERT I.D.'s | 11,452 | |
| picnupthepcs | ||
| Over 40 Different Types Of Seizures - Revised | 10,070 | |
| spiz | ||
| electrical shock in head? | 9,454 | |
| Maggie | ||
| View all Forums | ||
| Title | Posted | |
|---|---|---|
| The Greatest Experience!!!! | Aug 9, 2009 | |
| rachgamboa | ||
| Some new random thoughts | Sep 14, 2009 | |
| MichaelK | ||
| View all Blogs | ||
| Title | Posted | |
|---|---|---|
| same dose for 6 years possible unidentified seizures | Feb 9, 2010 | |
| mash4077 | ||
| Well, I know.... (Question at bottom of blog.) | Feb 9, 2010 | |
| quesofresco | ||
| nightmares | Feb 9, 2010 | |
| becky89 | ||
| i need to vent... | Feb 8, 2010 | |
| jacky99 | ||
| michelle | Feb 8, 2010 | |
| michelle41 | ||
| Etiology of a Housebound Visionary | Feb 8, 2010 | |
| tigro65 | ||
| Anyone w/ temporal lobe epilepsy and not on medication? | Feb 8, 2010 | |
| hazel baum | ||
| MY 1ST BLOG :) | Feb 8, 2010 | |
| awalkingmiracle | ||
| I hate the hospital. | Feb 8, 2010 | |
| Shenoah | ||
| Visit to a doctor - February 2010 | Feb 8, 2010 | |
| MichaelK | ||
| View all Blogs | ||
| Title | Page Views | |
|---|---|---|
| Inspirational Quote - My Own Personal Inner Thoughts | 8,007 | |
| Butterflygrl | ||
| my partial complex seizures | 3,872 | |
| Zanna1211 | ||
| Topomax... The Dreaded......... | 3,654 | |
| Dr Jason | ||
| Brain Zaps, tics & twitches | 3,473 | |
| JudiS | ||
| side effects of phenobarb. | 3,073 | |
| pksmom | ||
| Feeling Sick | 2,929 | |
| JBJ1984 | ||
| How can you tell if a sleep seizure happens? | 2,891 | |
| epl_controller | ||
| Tegretol XR and ANXIETY meds | 2,811 | |
| Butterflygrl | ||
| TYLENOL, AEDs & SEIZURES | 2,732 | |
| cmscribbles | ||
| Nonepileptic "Events" vs. "Seizures" | 2,601 | |
| teft | ||
| View all Blogs | ||
| Title | Posted | |
|---|---|---|
| Treating Depression with Epilepsy | Feb 4, 2010 | |
| mypetitmal | ||
| Burm80 | Feb 1, 2010 | |
| burm80 | ||
| WHO NEEDS A SEIZURE ALERT DOG | Jan 19, 2010 | |
| MOMMY HOLLIE | ||
| surgery group | Dec 20, 2009 | |
| bobby chen | ||
| Parents of Adult Children with Epilepsy | Nov 22, 2009 | |
| askadis | ||
| Grandparents of grandchildren with Epilepsy | Nov 14, 2009 | |
| EmiliesGrandma | ||
| neeraj clinic, rishikesh,india | Nov 14, 2009 | |
| ankita gupta | ||
| Project Uplift | Nov 4, 2009 | |
| tamliniscute | ||
| SEIZURE FREE | Nov 3, 2009 | |
| gracie9933 | ||
| EPILEPSY SUPPORT GROUP NORTH CAROLINA | Oct 9, 2009 | |
| Roxanne D | ||
| View all Groups | ||
| Title | Posted | |
|---|---|---|
| My Epilepsy Story | Sep 11, 2009 | |
| Kelly G. | ||
| Sudden and Awful | Oct 13, 2009 | |
| kel7 | ||
| View all Stories | ||
| Title | Posted | |
|---|---|---|
| Do I really have seizures? | Feb 9, 2010 | |
| Elmwoody | ||
| Looking for answers... | Feb 9, 2010 | |
| BSimons | ||
| Finding myself through the years | Feb 8, 2010 | |
| starlitgemini | ||
| Too many times doing the fish!!! | Feb 8, 2010 | |
| Jeffrey Resetar | ||
| My First story | Feb 8, 2010 | |
| eggcoo | ||
| my beautiful 6yr old boy | Feb 8, 2010 | |
| kaiden | ||
| My son has Rolandic Epilepsy | Feb 8, 2010 | |
| klabiche | ||
| My mother's epilepsy | Feb 8, 2010 | |
| Raymond Loh | ||
| A married man with a sick wife | Feb 7, 2010 | |
| russell11 | ||
| Many changes I had and continue to have. | Feb 7, 2010 | |
| Its Me | ||
| View all Stories | ||
| Title | Page Views | |
|---|---|---|
| Jessica Roiz | 2,294 | |
| kroiz | ||
| (TLE) seizures, insurance company denies me for health care due to epilepsy | 888 | |
| wenko | ||
| my story | 473 | |
| snoby | ||
| Always Have On Clean Underwear | 449 | |
| crashllama | ||
| Kelly's Life With Epilepsy | 421 | |
| kjcanada1979 | ||
| my brain has died a thousand deaths........... | 401 | |
| banffgirl | ||
| What My Seizures Are Like...... | 382 | |
| javaman | ||
| Nocturnal grand mal seizures (primary generalized epilepsy) | 341 | |
| karalyeva | ||
| Temporal Lobe Epilepsy | 337 | |
| Life......... | 333 | |
| dizzygal | ||
| View all Stories | ||
