What is an electroencephalogram (EEG). How is an EEG performed. When is an EEG used. What are the different types of EEG tests. What conditions can an EEG help diagnose. How should you prepare for an EEG test. What happens during an EEG procedure.

What is an Electroencephalogram (EEG)?

An electroencephalogram, commonly known as EEG, is a non-invasive medical test that records electrical activity in the brain. This sophisticated diagnostic tool provides valuable insights into brain function and helps medical professionals diagnose various neurological conditions.

During an EEG, small sensors called electrodes are attached to the scalp using a special adhesive. These sensors detect the electrical signals produced by brain cells (neurons) as they communicate with each other. The signals are then amplified and recorded by a machine, producing a detailed map of brain activity that can be analyzed by a specialist.

How does an EEG work?

The human brain consists of billions of neurons that constantly transmit electrical impulses to communicate. An EEG captures these electrical signals and translates them into wave patterns. Different wave patterns can indicate various brain states or potential abnormalities.

• Delta waves: Slow waves associated with deep sleep
• Theta waves: Often seen during light sleep or drowsiness
• Alpha waves: Present during relaxed wakefulness
• Beta waves: Observed during active thinking and concentration
• Gamma waves: Linked to higher cognitive functions and information processing

Applications and Uses of EEG Testing

EEG is a versatile diagnostic tool used in various medical scenarios. Its primary application is in the diagnosis and management of epilepsy, but it has numerous other uses as well.

Diagnosing and Monitoring Epilepsy

Epilepsy is a neurological disorder characterized by recurrent seizures. An EEG can help doctors:

• Confirm a diagnosis of epilepsy
• Identify the type of epilepsy
• Locate the origin of seizures in the brain
• Determine appropriate treatment options
• Monitor the effectiveness of anti-epileptic medications

Other Conditions Evaluated with EEG

Beyond epilepsy, EEG can assist in the diagnosis and management of various neurological conditions:

1. Sleep disorders (e.g., sleep apnea, narcolepsy)
2. Brain tumors
3. Stroke
4. Dementia and Alzheimer’s disease
5. Head injuries and concussions
6. Encephalitis (brain inflammation)
7. Attention deficit hyperactivity disorder (ADHD)
8. Disorders of consciousness (e.g., coma, vegetative state)

Types of EEG Tests and Their Purposes

There are several types of EEG tests, each designed to capture specific information about brain activity. The choice of test depends on the patient’s symptoms and the suspected condition.

Routine EEG

A routine EEG is the most common type of test, typically lasting 20 to 40 minutes. During this procedure, patients are asked to relax and may be instructed to perform simple tasks such as opening and closing their eyes or breathing deeply (hyperventilation). In some cases, a flashing light test (photic stimulation) may be used to provoke certain brain responses.

Sleep EEG

A sleep EEG is performed while the patient is asleep. This test can provide valuable information about sleep disorders and may reveal abnormalities not apparent during waking hours. In some cases, patients may be asked to stay awake the night before the test to ensure they can sleep during the procedure. This variation is called a sleep-deprived EEG.

Ambulatory EEG

An ambulatory EEG involves continuous recording of brain activity over an extended period, typically 24 to 72 hours. Patients wear a portable EEG device and can go about their daily activities while the test is in progress. This type of EEG is particularly useful for capturing infrequent events or examining how brain activity changes throughout the day and night.

Video EEG Monitoring

Video EEG monitoring combines continuous EEG recording with simultaneous video recording of the patient. This test is often used to diagnose epilepsy and to characterize seizures. It allows doctors to correlate observed behaviors with specific EEG patterns, providing a comprehensive understanding of seizure activity.

Preparing for an EEG Test: What You Need to Know

Proper preparation can help ensure accurate EEG results and a comfortable experience for the patient. Here are some key points to consider when preparing for an EEG:

• Follow any specific instructions provided by your healthcare provider
• Wash your hair the night before or the morning of the test, avoiding hair products like gels or sprays
• Eat normally and take your regular medications unless instructed otherwise
• Avoid caffeine and other stimulants for several hours before the test
• Bring a list of all medications you’re currently taking
• Wear comfortable clothing that’s easy to remove or adjust
• Consider bringing a hat or scarf to cover your hair after the test, as it may be messy from the electrode paste

Is it necessary to shave your head for an EEG? In most cases, no. Modern EEG electrodes can be applied without shaving the scalp. However, in rare instances where long-term monitoring is required, small areas might need to be shaved to ensure proper electrode contact.

The EEG Procedure: What to Expect During the Test

Understanding what happens during an EEG can help alleviate anxiety and ensure a smooth testing experience. Here’s a step-by-step breakdown of a typical EEG procedure:

1. You’ll be asked to lie down on a bed or recline in a comfortable chair
2. A technician will measure your head and mark the positions for electrode placement
3. The marked areas will be cleaned to ensure good contact
4. Electrodes (usually 16 to 25) will be attached to your scalp using a special adhesive paste
5. The electrodes will be connected to the EEG machine via wires
6. You’ll be asked to relax and remain still to minimize muscle movement artifacts
7. The technician may ask you to perform simple tasks like opening/closing your eyes or breathing deeply
8. In some cases, a flashing light test may be conducted
9. The entire procedure typically lasts 60 to 90 minutes, including setup and cleanup

Are there any risks associated with an EEG test? EEG is generally considered a safe procedure with no significant risks. Some patients may experience mild discomfort from the electrode adhesive or develop a temporary headache from the pressure of the electrodes. In rare cases, the flashing light test may trigger a seizure in patients with photosensitive epilepsy, but this is closely monitored and managed by the medical team.

Interpreting EEG Results: What Do They Mean?

After the EEG test, a neurologist or clinical neurophysiologist will analyze the recorded brain wave patterns. The interpretation of EEG results requires specialized expertise, as the patterns can be complex and subtle.

Normal EEG Results

A normal EEG shows brain wave patterns that are appropriate for the patient’s age and state of consciousness. However, it’s important to note that a normal EEG does not necessarily rule out all neurological conditions, as some abnormalities may not be present during the testing period.

Abnormal EEG Results

Abnormal EEG patterns can indicate various conditions, including:

• Epilepsy: Characterized by specific spike and wave patterns
• Sleep disorders: Abnormal sleep stage transitions or unusual patterns during sleep
• Brain tumors: Focal slowing or abnormal rhythms in specific brain areas
• Encephalitis: Generalized slowing of brain activity
• Stroke: Asymmetrical activity between brain hemispheres
• Dementia: Generalized slowing and loss of normal rhythms

How long does it take to get EEG results? The time frame for receiving EEG results can vary depending on the healthcare facility and the complexity of the test. In some cases, preliminary results may be available within a few days, while more detailed analysis can take up to two weeks.

Advances in EEG Technology and Future Applications

The field of EEG is continually evolving, with new technologies and applications emerging. Some exciting developments include:

High-Density EEG

High-density EEG systems use a larger number of electrodes (64 to 256) to provide more detailed spatial resolution of brain activity. This technology allows for more precise localization of brain functions and abnormalities.

Wireless and Wearable EEG Devices

Advances in miniaturization and wireless technology have led to the development of portable, wearable EEG devices. These systems offer the potential for long-term monitoring in natural environments, which could revolutionize the diagnosis and management of neurological conditions.

EEG in Brain-Computer Interfaces

EEG is playing a crucial role in the development of brain-computer interfaces (BCIs). These systems allow direct communication between the brain and external devices, offering hope for individuals with severe motor disabilities.

AI and Machine Learning in EEG Analysis

Artificial intelligence and machine learning algorithms are being developed to assist in the interpretation of EEG data. These tools have the potential to improve the accuracy and speed of EEG analysis, leading to faster and more precise diagnoses.

What potential applications might EEG have in the future? Some exciting possibilities include:

• Early detection of neurodegenerative diseases like Alzheimer’s
• Personalized treatment plans for psychiatric disorders
• Enhanced neurorehabilitation techniques for stroke patients
• Improved monitoring of anesthesia depth during surgery
• Advanced neurofeedback therapies for various conditions

EEG in Clinical Practice: Challenges and Considerations

While EEG is a valuable diagnostic tool, it’s important to understand its limitations and the challenges faced in clinical practice.

Interpretation Challenges

EEG interpretation requires significant expertise and experience. The complexity of brain wave patterns and the potential for artifacts (non-brain electrical signals) can make accurate interpretation challenging.

Variability in Results

EEG results can vary based on factors such as the patient’s state of alertness, medications, and even the time of day. This variability means that multiple EEG tests may sometimes be necessary for a definitive diagnosis.

Limited Spatial Resolution

While EEG provides excellent temporal resolution (ability to detect rapid changes in brain activity), its spatial resolution is limited compared to imaging techniques like MRI. This can make it difficult to precisely localize the source of abnormal activity within the brain.

Access to Specialized Equipment and Expertise

High-quality EEG testing requires specialized equipment and trained personnel, which may not be readily available in all healthcare settings, particularly in rural or underserved areas.

How can these challenges be addressed? Some potential solutions include:

• Continued professional education and training for EEG technicians and interpreters
• Development of standardized protocols for EEG acquisition and interpretation
• Integration of EEG with other diagnostic modalities for a more comprehensive assessment
• Telemedicine initiatives to improve access to EEG expertise in remote areas
• Ongoing research to enhance EEG technology and analysis techniques

In conclusion, electroencephalography (EEG) remains a cornerstone of neurological diagnosis and research. Its non-invasive nature, relatively low cost, and ability to provide real-time information about brain function make it an invaluable tool in modern medicine. As technology continues to advance, we can expect EEG to play an even more significant role in understanding and treating neurological disorders, potentially opening new avenues for personalized medicine and brain-computer interaction.

Electroencephalogram (EEG) – NHS

An electroencephalogram (EEG) is a recording of brain activity.

During this painless test, small sensors are attached to the scalp to pick up the electrical signals produced by the brain.

These signals are recorded by a machine and are looked at by a doctor.

The EEG procedure is usually carried out by a highly trained specialist, called a clinical neurophysiologist, during a short visit to hospital.

When an EEG is used

An EEG can be used to help diagnose and monitor a number of conditions affecting the brain.

It may help identify the cause of certain symptoms – such as seizures (fits) or memory problems – or find out more about a condition you’ve already been diagnosed with.

The main use of an EEG is to detect and investigate epilepsy, a condition that causes repeated seizures. An EEG will help your doctor identify the type of epilepsy you have, what may be triggering your seizures and how best to treat you.

Less often, an EEG may be used to investigate other problems, such as:

• dementia
• head injury and concussion
• brain tumours
• encephalitis (brain inflammation)
• sleep disorders, such as sleep apnoea.

Preparing for an EEG

Your appointment letter will mention anything you need to do to prepare for the test.

Unless told otherwise, you can usually eat and drink beforehand and continue to take all your normal medication.

To help the sensors stick to your scalp more easily, you should make sure your hair is clean and dry before arriving for your appointment, and avoid using products such as hair gel and wax.

You might want to bring a hairbrush or comb with you, as your hair may be a bit messy when the test is finished. Some people bring a hat to cover their hair until they can wash it at home afterwards.

How an EEG is carried out

There are several different ways an EEG recording can be taken. The clinical neurophysiologist will explain the procedure to you and can answer any questions you have. 

You’ll also be asked whether you consent to treatment for the various parts of the test to be carried out. This may include video consent for some EEGs.

Before the test starts, your scalp will be cleaned and about 20 small sensors called electrodes will be attached using a special glue or paste. These are connected by wires to an EEG recording machine.

Sensors called electrodes are attached to the head (usually with glue or paste) and connect to an EEG recording machine. You’ll sit or lie down for an EEG.

Credit:

Phanie / Alamy Stock Photo https://www.alamy.com/stock-photo-woman-undergoing-an-electroencephalogram-eeg-limoges-hospital-france-72431574.html?pv=1&stamp=2&imageid=7AA22C91-664F-4D38-8619-582AA92C0168&p=218158&n=0&orientation=0&pn=1&searchtype=0&IsFromSearch=1&srch=foo%3dbar%26st%3d0%26pn%3d1%26ps%3d100%26sortby%3d2%26resultview%3dsortbyPopular%26npgs%3d0%26qt%3dE5RF5X%26qt_raw%3dE5RF5X%26lic%3d3%26mr%3d0%26pr%3d0%26ot%3d0%26creative%3d%26ag%3d0%26hc%3d0%26pc%3d%26blackwhite%3d%26cutout%3d%26tbar%3d1%26et%3d0x000000000000000000000%26vp%3d0%26loc%3d0%26imgt%3d0%26dtfr%3d%26dtto%3d%26size%3d0xFF%26archive%3d1%26groupid%3d%26pseudoid%3d%7bA883FDE5-7F3D-4472-81F5-B61111916852%7d%26a%3d%26cdid%3d%26cdsrt%3d%26name%3d%26qn%3d%26apalib%3d%26apalic%3d%26lightbox%3d%26gname%3d%26gtype%3d%26xstx%3d0%26simid%3d%26saveQry%3d%26editorial%3d1%26nu%3d%26t%3d%26edoptin%3d%26customgeoip%3d%26cap%3d1%26cbstore%3d1%26vd%3d0%26lb%3d%26fi%3d2%26edrf%3d0%26ispremium%3d1%26flip%3d0%26pl%3d

Routine EEG recordings usually take 20 to 40 minutes, although a typical appointment will last about an hour, including some preparation time at the beginning and some time at the end.

Other types of EEG recording may take longer.

Types of EEG

Routine EEG

A routine EEG recording lasts for about 20 to 40 minutes.

During the test, you’ll be asked to rest quietly. You will usually be asked to open or close your eyes from time to time. In most cases, you’ll also be asked to breathe in and out deeply (called hyperventilation) for a few minutes.

A flashing light may also be used to see if this affects your brain activity.

Sleep EEG or sleep-deprived EEG

A sleep EEG is carried out while you’re asleep. It may be used if a routine EEG does not give enough information, or to test for sleep disorders.

In some cases, you may be asked to stay awake the night before the test to help ensure you can sleep while it’s carried out. This is called a sleep-deprived EEG.

Ambulatory EEG

An ambulatory EEG is where brain activity is recorded throughout the day and night over a period of one or more days. The electrodes will be attached to a small portable EEG recorder that can be clipped onto your clothing.

You can continue with most of your normal daily activities while the recording is being taken, although you’ll need to avoid getting the equipment wet.

Video telemetry

Video telemetry, also called video EEG, is a special type of EEG where you’re filmed while an EEG recording is taken. This can help provide more information about your brain activity.

The test is usually carried out over a few days while staying in a purpose-built hospital suite.

The EEG signals are transmitted wirelessly to a computer. The video is also recorded by the computer and kept under regular surveillance by trained staff.

Invasive EEG-telemetry

This EEG is not common, but it may be used to check if surgery is possible for some people with more complex epilepsy.

It involves surgery to place electrodes directly on the brain to find out exactly where the seizures are coming from.

What happens after an EEG

When the test is finished, the electrodes will be removed and your scalp will be cleaned. Your hair will probably still be a bit sticky and messy afterwards, so you may want to wash it when you get home.

You can usually go home soon after the test is finished and return to your normal activities. You might feel tired after the test, particularly if you had a sleep or sleep-deprived EEG, so you may want someone to pick you up from hospital.

You normally will not get your results on the same day. The recordings will need to be analysed first and will be sent to the doctor who requested the test. They can discuss the results with you a few days or weeks later.

Are there any risks or side effects?

The EEG procedure is painless, comfortable and generally very safe. No electricity is put into your body while it’s carried out. Apart from having messy hair and possibly feeling a bit tired, you normally will not experience any side effects.

However, you may feel lightheaded and notice a tingling in your lips and fingers for a few minutes during the hyperventilation part of the test. Some people develop a mild rash where the electrodes were attached.

If you have epilepsy, there’s a very small risk you could have a seizure while the test is carried out, but you’ll be closely monitored and help will be on hand in case this happens.

Video: epilepsy research – EEG

This video covers the benefits of participating in EEG research.

Media last reviewed: 5 August 2022
Media review due: 5 August 2025

Page last reviewed: 05 January 2022
Next review due: 05 January 2025

EEG test – Better Health Channel

The electroencephalogram (EEG) is a medical test used to measure the electrical activity of the brain, via electrodes applied to your scalp. This procedure is completely painless and can be performed without shaving any of your hair. EEG can help diagnose a number of conditions, including epilepsy, sleep disorders and brain tumours. Another name for EEG is brain wave test.

Conditions diagnosed by EEG

Normal brain waves occur at a rate of up to 30 per second, but in someone with epilepsy, for example, the EEG may show bursts of abnormal discharges in the form of spikes and sharp wave patterns. Suspected epilepsy is the most common reason for an EEG.

Other conditions that may be diagnosed with the aid of an EEG include:

• Sleep disorders (such as narcolepsy)
• Head injuries
• Brain infection
• Brain haemorrhage
• Alzheimer’s disease
• Degeneration of brain tissue
• Metabolic conditions that affect brain tissue
• Hormonal conditions that affect brain tissue
• Certain disorders of the central nervous system
• Stroke
• Brain tumour
• Brain death.

Medical issues to consider

An abnormal EEG doesn’t automatically mean that you, for example, have epilepsy. The EEGs of babies and young children can often record irregular patterns that don’t mean anything, or the irregularities may flag previously diagnosed neurological conditions such as cerebral palsy. On the other hand, a normal EEG doesn’t rule out epilepsy either. Sometimes, a person with epilepsy will only display abnormal brain waves during a seizure.

EEG procedure

Your hair must be thoroughly clean, but most importantly dry. A number of electrodes are applied to your scalp (generally between 8 and 23, depending on the condition under investigation). A gel may be applied to help the electrodes to stick firmly in place and improve recordings.

You will need to lie quietly to avoid any electrical interference from muscle contractions. Sometimes, you may be asked by the doctor to open and close your eyes and to breathe heavily. Lights may be flashed before your eyes. An EEG usually takes from 30 to 60 minutes to complete. Sometimes, a sleep recording is also required. If the patient is a baby or young child, it helps if the parents delay the child’s nap until the time of the EEG.

Sedatives (medications to help sleep) may be needed if sleep won’t come naturally during the test. Some EEG testing centres may record a video of your tests to help with diagnosis.

Immediately after the EEG

Once the test is complete, the electrodes are removed and you are allowed to get up. The results need to be analysed at a later stage by a neurologist (a doctor who specialises in brain disorders).

Generally, if there is no abnormality to the brain’s electrical activity, the pattern of ‘peaks and valleys’ charted by the EEG should be fairly regular. If excited, the pattern will show considerable variation, and any departure from the regular pattern can indicate abnormalities.

Complications of EEG

EEG is a safe test with no side effects. However, a person with epilepsy may experience a seizure, triggered by the various stimuli used in the procedure, including the flashing lights. (This is not seen as a ‘complication’ by medical staff, because a seizure during an EEG can greatly help in diagnosis.)

Taking care of yourself at home

EEG is a safe procedure. Be advised by your doctor, but generally, there are no special instructions for after-care. However, you will need to wash your hair thoroughly to remove all traces of gel and other fluids.

Long-term outlook

The EEG technologist can’t interpret the test results on the spot. The EEG recording must be analysed by a neurologist, who then sends the results to your doctor. It is important to make a follow-up appointment with your doctor. In many cases, the test results are sent to your doctor within 48 hours of the test. Treatment depends on the diagnosis.

Other diagnostic tests

Other diagnostic tests depend on the condition under investigation. For example, magnetic resonance imaging (MRI) scans and computed tomography (CT) scans may be used in the case of suspected brain tumour.

Where to get help

• Your doctor
• Neurologist

Things to remember

• The electroencephalogram (EEG) is a medical test used to measure the electrical activity of the brain.
• A number of electrodes are applied to your scalp.
• EEG can help diagnose a number of conditions including epilepsy, sleep disorders and brain tumours.

Electroencephalography. Technical details

Electroencephalography (EEG) is a method of studying the brain based on recording its bioelectrical potentials. Specifically, in each channel, the potential difference between the active and reference electrodes is measured – i.e. between these electrodes flows a weak alternating electric current produced by the patient. Since the current is weak, there must be minimal resistance between the electrodes! (impedance).

With the help of EEG, it is possible to objectively study the functional state of the brain and identify the degree and localization of its damage. The method is most informative in the diagnosis of epilepsy. EEG data help to differentiate various forms of seizures, to establish the localization of the epileptic focus, as well as to monitor the effectiveness of drug therapy.

It should be remembered that the EEG records the total electrical activity from relatively large areas of the head surface. At the same time, in addition to the activity of the cerebral cortex, myographic activity of the muscles of the scalp and masticatory muscles, muscles of the eyeballs and eyelids, a rheogram and an ECG artifact can be recorded when the EEG electrode is located above the blood vessels.

So, for EEG recording, you need a number of electrodes on the head, installed at certain points, as well as a reference electrode (s) and a ground electrode.

Reference electrodes, classically located on the earlobes, designated Ref (R), but can also be placed in other places, for example, on the mastoid processes behind the ears, in the midline, between the Fz and Cz electrodes (electrodes located in the midline , are denoted by the index – “z”, from “zero”, i. e. Zero). Electrodes that are located in the left hemisphere are usually denoted by odd numbers, and those in the right hemisphere by even numbers. It is obligatory to have a ground electrode, which can be located anywhere on the head (most often it is installed between the Fp1 and Fp2 electrodes on the forehead, at the point Fpz).

A complete 10-20 standard circuit provides 21 electrodes (including 1 ground electrode and 1 reference).

The locations of the electrical activity of the brain are marked with letters, in accordance with the areas over which the electrodes are located:

0003

Frontal – F (frontalis)

Temporal – T (temporalis)

International electrode layout.

The International 10-20% Scheme, or simply the 10-20 Scheme, was developed by Jasper H. in 1958 to standardize terminology and describe the location of scalp electrodes so that EEG recordings can be comparable, regardless of the laboratory and physician analyzing the study . It is currently the international standard for electrode placement. It is used when sticking collodion electrodes, as well as in EEG caps, which appeared much later.

This scheme involves measuring the distance from the bony landmarks of the skull, followed by the calculation of the intervals between the electrodes in percent, to determine the location of the electrodes. The principle is as follows:

1) The distance between the points Nasion (bridge of the nose) and Inion (protrusion of the occiput) is measured.
At 10% of the obtained distance, above the occiput, there is a point Oz and a line of occipital electrodes (O1, O2). Anterior to this line, at a distance of 20% is the point Pz and the line of the parietal electrodes (P3, P4), after another 20% – the point Cz and the line of the central electrodes (C3, C4), and after another 20% – the point Fz and the line of the frontal electrodes (F3, F4). The frontal pole electrodes (Fp1 and Fp2) are located on a line 10% above the Nasion point and 20% from the line of the forehead electrodes. At the point of intersection of this line with the longitudinal one, there is a point Fpz.

2) The second main distance is measured between the parotid points (the indentation immediately above the tragus is taken as a reference), along a line that passes through the middle of the first distance. It is also divided into segments as a percentage: 10% above the ear canals, on each side, are the temporal electrodes (T3 and T4), 20% above the temporal electrodes are the aforementioned central electrodes (C3, C4).

3) The third distance is measured as the circumference of the head, however, the tape is laid strictly through the already found points Fpz, T3, Oz and T4 (along the circumference). Half of the distance obtained is taken as 100% and, based on this, 10% to the left and right of Fpz are calculated to determine the pole frontal electrodes (Fp1 and Fp2, respectively) and 10% of Oz, to determine the occipital electrodes (O1 and O2) . Also on this line are:
– lower frontal electrodes (F7 and F8), at a distance of 20% from Fp1 (posteriorly) and T3 (anteriorly) and similarly on the other side.
– posterior temporal electrodes (T5 and T6), at a distance of 20% from T3 (posteriorly) and O1 (anteriorly) and similarly on the other side.

As already mentioned, sagittal electrodes are placed along the midline – frontal (Fz), central (Cz), parietal (Pz). Points Fpz and Oz are not used to install active electrodes in the 10-20 system.

By the size of segments of 10 and 20%, this scheme got its name.

Marking the head for installing collodion electrodes:

1. Laying the measuring tape from Nasion to Inion strictly along the midline, we measure the first distance, and on its half, to the right and left of the tape, we put intermediate marks.

2. Measure the distance between the parotid points, laying the edge of the tape through the above intermediate marks.
In the middle of this distance there will be a confirmed point Cz. Without releasing the tape, you can mark points T3, T4, C3 and C4,

Example: We got 35 cm. 10% of 35 = 3.5 cm.
From each round point, along the same line, we measure up 3.5 cm to the right and left – we find points T3 and T4.
Divide the distance from T3 to Cz in half, find C3
Divide the distance from T4 to Cz in half, find C4

3. Lay the tape again between the points Nasion and Inion, but this time laying the edge of the tape through the already confirmed
point Cz.

Example: 40 cm specified distance. 10% of 40 = 4 cm. So, from Nasion and Inion we measure 4 cm up along the midline and mark the conditional points Fpz and Oz.
We divide in half the distance from the point Cz and the point Oz, we get the point Pz. Similarly, we divide in half the distance from the point Cz to the point Fpz and find the point Fz.

4. As mentioned above, we measure the circumference of the head strictly through the already found points Fpz, T3, Oz and T4 (along the circumference). Half of the obtained distance is taken as 100%. Based on this, 10% to the left and right of Fpz ( along this circle ) are calculated to determine the pole frontal electrodes (Fp1 and Fp2, respectively) and 10% of Oz, to determine the occipital electrodes (O1 and O2).

Example: head circumference of 60 cm is 200%. Half of this = 30 cm. 10% of 30 = 3 cm.

5. Find F7 and F8; T5 and T6.

Divide the distance from Fp1 to T3 in half, find F7
Divide the distance from Fp2 to T4 in half, find F8
and
Divide the distance from T3 to O1 in half, find T5
Divide the distance from T4 to O2 in half, find T6

90 002 Test yourself: the above points should lie on your measured head circumference.

6. Find F3 and F4; P3 and P4.

If you lay the measuring tape in an arc through the points Fp1-C3-O1, you will get a “parallel” (see fig. 1), which intersects with the “meridian” going through the points F7-Fz-F8 (see fig. 2) at point F3 .
Similarly, the “parallel” Fp2-C4-O2 intersects with the same “meredian” at the point F4 .

1 Fig. 2 Fig. 3

In the same way, by laying the “meridian” through the points T5-Pz-T6 (see Fig. 3), you can calculate the points P3 and P4 .

In other words, point F3 is halfway between points Fp1-C3 and Fz-F7.
Similarly, point F4 is halfway between points Fp2-C4 and Fz-F8.
Same with electrodes P3 and P4.

In practice, in addition to the electrodes installed according to the 10-20 system, additional electrodes are used to locate which the same principle is used. We are talking about the electrodes of the zygomatic arch (F9, F10, T9, T10, P9 and P10). How to locate them?

Remember the distance measured from the parotid points through Cz. Each of the listed electrodes is 10% lower than the corresponding electrodes lying on the circumference of the head:
– F9 and F10 are 10% lower than the F7 and F8 electrodes, respectively. That is, they lie on the zygomatic bone.
– T9 and T10 are 10% lower than the T3 and T4 electrodes, respectively. In fact, they lie on the parotid points.
– P9 and P10 are 10% lower than the electrodes T5 and T6, respectively. They lie on the mastoid processes of the skull (mastoideus).

The use of these electrodes can help localize interictal epileptiform activity and the EEG onset. In particular, anterior zygomatic electrodes, according to some authors, are non-invasive analogues of sphenoidal electrodes.

Mountings.

Recorded EEG data can be presented in different ways. For this, there are various wiring diagrams.

The most common way to monitor a recording is to use referential editing – this is how the amplifier perceives the data.

All other montages are reconstructions resulting from potential difference mathematical calculations based on reference montage data.

Features of wiring diagrams (from the point of view of a technician) :

– in referential installation it is convenient to control the quality of electrode application, judging by the interference in one or another lead.

– in bipolar mounting (longitudinal chain) so-called. “drenched electrodes” – i.e. electrodes, between which a path of electrically conductive gel was formed, therefore, they became a single electrode, inside which there is no potential difference, just as there is no potential difference between the different ends of the nail. On the EEG, in this case, in the lead, consisting of a pair of “filled” electrodes (for example, F3-C3), an isoline is recorded.

– transverse mounting. In fact – the same bipolar installation, only the chains of leads go in the transverse direction. Similarly, in a flooded pair of electrodes (for example, F7-F3), an isoline will be recorded. The peculiarity is that if you have F7-F3 filled in, then everything will be fine in the bipolar (previous) installation! (but the EEG data is incorrect).

Prepared by: EEG assistant Kozlova M.A. and head. laboratory of video-EEG monitoring Troitsky A.A.

Electroencephalography (EEG)

January 21, 2016

A complete and high-quality diagnosis of disorders that occur in the brain and have a psychoneurological nature is impossible without the use of hardware research methods, the main of which is EEG (electroencephalography).

Essence of the method

This method of examining brain activity is based on a comprehensive and in-depth analysis of electrical impulses that are generated by groups of neurons. These weak electrical discharges are captured using a group of electrodes fixed on the head of the person being examined, and after the necessary amplification, they are displayed on the electroencephalograph monitor. To save the data on the survey, information about it is recorded in the computer’s memory or visualized in the form of a graph on a paper tape, which is called an electroencephalogram of the brain.

Identifiable brain abnormalities

Electrical impulses generated by neurons have a certain frequency and amplitude. Depending on the psycho-emotional state of a person, these indicators may vary. Therefore, having studied a person’s electroencephalogram, specialists from a self-supporting polyclinic located at the “Youth Library” can find out the state of his brain, both in general and in certain departments.

Deciphering the results of the EEG of the brain makes it possible to identify:

– benign or malignant tumors;

– insufficient level of blood supply to the brain;

– pathological deviations in the work of the central nervous system, provoked by infectious diseases;

– epilepsy;

– developing neuroses of any etiology;

– the presence of deviations in mental development.

An analysis of the EEG of the brain allows the attending physician not only to clarify the final diagnosis, but also to identify positive changes in the patient’s condition, and also to carry out the necessary adjustment of the drugs used during the treatment.

Preparing and conducting a survey

In order for the data obtained during the examination to be reliable, before passing the EEG, it is necessary:

– exclude from the diet foods that stimulate the central nervous system;

– wash your hair well to remove the remnants of hair care products;

– eat well.

During the examination, the patient lies down on a couch or sits down in a chair, after which a special cap is put on his head, to which electrodes are attached in certain places. Now the person undergoing the examination needs to relax as much as possible and wait for the end of the procedure, which can last up to two hours.

Often, electroencephalography is accompanied by sound or light signals given in a chaotic manner. This is done to enhance the information content of the electroencephalogram or to identify some difficult-to-diagnose diseases. Sometimes it is required to determine the activity of the brain excited by an excess of oxygen.