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The method of electroencephalography is an accurate and objective method of recording the bioelectrical activity of the brain, used both in scientific research and in clinical practice. However, achieving a high-quality result requires a lot of preparatory work. This chapter describes the technology for conducting electroencephalographic studies, their subsequent analysis, and presentation of results that are understandable to both a specialist neurophysiologist and a practicing neurologist. You will also find a description of the organization of the EEG study, the choice of scenario, functional tests, and the basics of forming a medical report. We will also consider individual issues of organizing an EEG study in people who have had a stroke, and multichannel and functional EEG studies.
National Research Nuclear University (MEPHI) Engineering Physics Institute of Biomedicine, Moscow, Russia
*Address all correspondence to: sergruss@yandex.ru
1. Introduction
Electroencephalography is an accessible method for objective diagnosis of the functional activity of the brain, widely used in modern neurology. The main reason for the modern use of electroencephalography in clinical diagnostics is the fact that there is no time delay between the level of nutrient supply to the nerve cell and changes in the total postsynaptic potential recorded using the electroencephalographic system, which is due to the absence of organelles in nerve cells that ensure the deposition of nutrients. This makes it possible to use the EEG for diagnosing brain processes with fast dynamics that are inaccessible to other technologies, in particular, fMRI. In practice, this makes it possible to observe the features of changes in cerebral hemoperfusion in the cortical regions of the cerebral hemispheres in real time. And taking into account the peculiarities of the EEG—technology to implement an economically accessible system of functional observation / control without significant risks of adverse effects on the subject.
However, the most significant issues limiting the use of EEG at present are the training of specialists who use in their daily work either primitive diagnostic technologies in the form of visualization-phenomenological analysis or controversial mathematical methods introduced into the EEG technique back in the era of analog devices, thanks to their accessibility and ease of implementation, but lacking a convincing scientific justification [1].
To understand the place of EEG in modern neurological diagnostics, these issues need to be considered in more detail. The issue of localization of the EEG signal source and its connection with brain structures were solved as early as by Penfield in the 1940s of the last century [2], using the “10-20” system of electrode placement on the scalp, which is still used today, which made it possible to create a triangulation model for determining the basic signal, as which W. Penfield used a focal epileptic discharge. Currently, these ideas are actively used in the photogrammetric localization system, actively promoted by Magstim Corporation (USA) [3].
But due to a lack of understanding of the need to build a triangulation model, as well as attempts to revise the technology from the standpoint of other functional methods, a significant simplification of the EEG methodology was formed and the further development of electroencephalography went in two ways: The first was the use of a routine study in outpatient practice, the purpose of which was diagnostic search and active detection of epilepsy in workers of certain specialties and industries, and the purpose of the second was to scientifically search for the relationship between functional and behavioral reactions caused by various objective factors (especially those associated with the development of intracranial volumetric formations) and changes in the general nature of the EEG signal. These studies made it possible to make a number of significant observations about the nature of slow-wave rhythmic phenomena and from the connection with processes accompanied by swelling of the nervous tissue and disorders of cerebral hemoperfusion processes; however, the lack of localization technology and the search for alternative solutions led to a loss of interest in EEG in the late 1990s of the last century, with the advent of affordable radiological diagnostic systems that made it possible to obtain a two-dimensional image understandable to most specialists, comparable to traditional anatomical drawings and postmortem examination data.
At present, the creation of systems for accurate localization of the position of EEG electrodes in space [4, 5, 6], as well as the development of the latest EEG diagnostic systems with a large number of active electrodes presented in the developments (3), has revived interest in electroencephalography as an accessible a method that makes it possible to study the processes of brain activity that have fast dynamics, which are inaccessible to systems using technologies for recording the dynamics of changes in cerebral microcirculation (MRI, near-infrared spectroscopy), and the development of software products for combining the results of a spatial representation of the EEG potential distribution on the scalp with radio imaging data methods [7] made it possible to obtain information on functional changes, comparable in accuracy to the methods of X-ray neuroimaging.
This led the International Federation of the Clinical Neurophysiology (IFCN) guidelines in 2017 to adopt official recommendations for the use of advanced lead localization systems and also recommended a gradual transition from using the “10-20” system to the “10-10” system [8]. This approach makes it possible to develop new ideas for creating a system of brain mapping (brain mapping), which allows recording various functional changes in cerebral activity in real time and making their direct connection with anatomical data [9].
The development of such systems will improve the quality of life and stroke patients and accelerate their return to an active social life, which has already been shown by a number of authors [10, 11, 12].
2. Registration of bioelectrical activity in a routine study
Important!
EEG registration begins with the procedure for checking the device for electrical safety!
Make sure that the instrument is connected to the network (control computer). Wires (especially mains power wires) do not have visible damage, which are not located near water or heat sources.
Carrying out functional stress tests may be associated with the risk of developing an epileptic seizure or other paroxysmal condition. Therefore, the specialist conducting the study must have the skills to provide resuscitation and also be able to call the resuscitation team.
2.1 Patient preparation
The patient comes to the study in a calm state with a clean head. Best of all, in the first half of the day, in order to avoid the consequences of psycho-emotional impact.
2.2 Start of the study
The patient is connected using an electrode interface (cap). It is necessary to make sure that the cap is clean and dry, and the helmet material and wires do not have visible damage.
Installation of electrodes is carried out by means of the international layout of electrodes “10-20.”
Installation of reference (ear) electrodes is carried out on the earlobes A1—left lobe and A2—right lobe using electrodes—clothespins.
If it is impossible to install ear electrodes (there are no clothespins in the packing or otherwise), reference electrodes are installed on the mastoid processes A1—left mastoid process and A2—right mastoid process.
After connecting the patient to the device, the photostimulator is installed at a distance of 20 cm from the eyes and the direction of the light flux is checked.
2.3 Next, we move on to working with the program
Fill out the patient card
We enter data into the card, including full name, age, and gender
Checking the installation of the current installation
Most often, the current editing of the recording is set automatically, but before examining, you need to make sure that the program settings have not changed.
Check the write speed
Write speed should be set to 30 mm per 1 second
Checking the amplitude sweep
Amplitude sweep set to 7 μV
Checking the settings of filtering values
The low-frequency limit is set to 0.5 Hz
The high end is set to 35 for normal exploration and 70 for advanced.
After checking the recording parameters, we start monitoring—a mode in which the device is turned on, but no data are written to the disk.
In monitoring mode, we check the characteristics of the curves and proceed to the impedance test.
Impedance test
The subelectrode resistance (impedance) shows the correct installation of the electrode and characterizes the contact of the electrode with the scalp. The impedance value must not exceed 10 kOm. At high impedance values, it is necessary to check the contact of the electrodes with the scalp, if necessary, remove the hair that has fallen under the electrode, add an electrically conductive gel, or thoroughly degrease the skin with an alcohol-containing solution and a cotton swab.
After stabilization of the impedance values (should be equal under all electrodes), we start recording with research.
Study recording
The study recording mode differs from monitoring in that the data are saved to the computer’s hard drive. Recording is the main survey mode!
During the study, the patient is presented with various functional tests, which, for ease of understanding, are combined into a single-study scenario.
The study is carried out for at least 20 minutes and includes the following procedures:
Background recording 3–5 minutes (but not less than 3 minutes)
Opening eyes—1 min. Closing eyes—1 min.
Background recording—3 min.
Test with photostimulation (rhythmic light flashes are presented with the help of a photostimulator):
Hz—10 sec.
Break 5 sec
2 Hz—10 sec.
Break 5 sec
3 Hz—10 sec.
Break 5 sec
4 Hz—10 sec.
Break 5 sec
5 Hz—10 sec.
Break 5 sec
25 Hz—10 sec.
Background recording—3 min.
Opening eyes—1 min. Closing eyes—1 min.
Background recording 1 min.
Hyperventilation—3 min.
Background recording—5 min.
Opening eyes—1 min. Closing eyes—1 min.
Study Termination
3.2 Children
In children and adolescents, it is sometimes difficult to make a full-fledged recording, according to the “10-20” system due to the small size of the head, and it is also difficult for children to remain still for a long time. At the same time, due to the functional immaturity of the structures of the child’s brain, the desired phenomena manifest themselves better than in adults. Thus, an EEG study in children takes at least 15 minutes and includes the following tests:
3.3 Scenario “Children”
Background recording 3 min
Eye opening—1 min. Eye closing—1 minute
Background recording—1 min.
Test with photostimulation (rhythmic light flashes are presented with the help of a photostimulator)
1 Hz—10 sec.
Break 5 sec
2 Hz—10 sec.
Break 5 sec
3 Hz—10 sec.
Break 5 sec
4 Hz—10 sec.
Break 5 sec
5 Hz—10 sec.
Break 5 sec
25 Hz—10 sec.
Background recording—1 min.
Opening eyes—1 min. Closing eyes—1 min.
Background recording—1 min.
Hyperventilation—3 min.
Background recording—3 min.
Opening eyes—1 min. Closing eyes—1 min.
Study termination
3.4 Epilepsy
When the diagnosis of “Epilepsy” is established, the study is carried out for 25 minutes, but not less than 20 minutes and includes the following procedures:
3.5 Scenario “Epilepsy”
Background recording 5 min
Opening eyes—1 min. Closing eyes—1 min.
Background recording—3 min.
Test with photostimulation (rhythmic light flashes are presented with the help of a photostimulator)
1 Hz—10 sec.
Break 5 sec
2 Hz—10 sec.
Break 5 sec
3 Hz—10 sec.
Break 5 sec
4 Hz—10 sec.
Break 5 sec
5 Hz—10 sec.
Break 5 sec
25 Hz—10 sec.
Continuous photo stimulation from 1 to 50 Hz
40 Hz—10 sec.
Break 5 sec
30 Hz—10 sec.
Break 5 sec
20 Hz—10 sec.
Background recording—3 min.
Opening eyes—1 min. Closing eyes—1 min.
Background recording—1 min.
Hyperventilation—3 min.
Background recording—3 min.
Hyperventilation—2 min
Background recording—3 min.
Opening eyes—1 min. Closing eyes—1 min.
Background recording—3 min.
Study termination
In patients who have had a cerebral stroke, of particular interest is the reaction of the bioelectrical activity of the brain to physical activity, which occurs as a result of impaired cerebral hemoperfusion and defective functioning of the collateral blood supply system.
3.6 Scenario “Stroke”
Background recording (passive relaxed wakefulness with closed eyes)—3 min
Opening eyes—1 min. Closing eyes—1 min.
Test with photostimulation (rhythmic light flashes are presented with the help of a photostimulator)
1 Hz—10 sec.
Break 5 sec
2 Hz—10 sec.
Break 5 sec
3 Hz—10 sec.
Break 5 sec
4 Hz—10 sec.
Break 5 sec
5 Hz—10 sec.
Break 5 sec
25 Hz—10 sec.
Background recording—1 min
Opening eyes—1 min. Closing eyes—1 min.
Motion test
Squeeze—unclench the right hand—3 min
Background recording—1 min
Opening eyes—1 min. Closing eyes—1 min.
Motion test
Squeezing—unclenching the left hand—3 min
Background recording—1 min
Opening eyes—1 min. Closing eyes—1 min.
Motion test
Squeeze—unclench both hands—3 min
Background recording—1 min
Opening eyes—1 min. Closing eyes—1 min.
Test with hyperventilation
Deep breathing—3 min
Opening eyes—1 min. Closing eyes—1 min.
Background recording (passive relaxed wakefulness with closed eyes)—3 min
Important!
With the appearance of paroxysmal epileptiform activity, the development of a seizure, the study stops!
4. Conducting standard functional stress tests in the study
4.1 Photostimulation
Photostimulation is carried out using a special device combined with an electroencephalograph, which makes it possible to produce rhythmic light flashes at a given frequency.
The color of the flash may be white or red, depending on the design of the device. The light source can be a gas discharge lamp or high-power LEDs.
4.2 Contraindications for the test
Pregnancy is a relative contraindication to a photostimulation test, as there is a risk of adverse effects on the fetus in the event of an epileptic seizure.
Important!
When using a photostimulator with a gas discharge lamp as a light source, never test with open eyes, due to the risk of eye damage from the powerful light flux of the gas discharge lamp!!!
4.3 Hyperventilation
During hyperventilation, the subject takes a deep breath (trying to fill the lungs as best as possible and exhale through slightly closed lips).
4.4 Contraindications for the test
Relative contraindications to the hyperventilation test:
History of indications of cardiac arrhythmias
Intracranial tumors of subtentorial localization
Myocardial infarction
Diabetes mellitus in the stage of decompensation
Acute intoxications
Chronic obstructive pulmonary disease
Frequent series of generalized and secondary generalized seizures
4.5 Absolute contraindications
Trauma to the upper respiratory tract
Paroxysmal ventricular arrhythmias
Acute period of myocardial infarction
Pneumothorax
In addition to the contraindications listed above, the hyperventilation test should not be continued if true epileptiform activity is clearly presented in the record, since the main goal of the test has been achieved, and its continuation may lead to the development of a clinical seizure, or in an unfavorable case, status epilepticus.
Important!
When performing the test, frequent, shallow, and ineffective breathing should be avoided, since in this case, the state of hyperoxia is not achieved and the test becomes ineffective.
Important!
The main task of a routine examination is to ESTABLISH A DIRECT RELATIONSHIP between the development of a functional disorder and the type of functional load imposed, which is confirmed by the development of pathological activity in the EEG recording!!!
In the absence of a direct connection between the development of a functional disorder and a provoking factor, it is concluded that further examination is necessary using long-term EEG recording technologies.
The purpose of the study: to identify a possible pathological response to functional loads, if there is a suspicion of the likelihood of developing a seizure, but no pathology is detected on a routine examination, but there are suspicions of the development of such.
The main objective of the study is to exclude the possibility of developing a seizure in workers of complex industries.
The study is based on repeated functional stress tests for a long time (up to 3 hours)
5.2 Study scenario
Background recording 5 min
Opening eyes—1 min. Closing eyes – 1 min.
Background recording—3 min.
Test with photostimulation (rhythmic light flashes are presented with the help of a photostimulator):
1 Hz—10 sec.
Break 5 sec
2 Hz—10 sec.
Break 5 sec
3 Hz—10 sec.
Break 5 sec
4 Hz—10 sec.
Break 5 sec
5 Hz—10 sec.
Break 5 sec
25 Hz—10 sec.
Background recording—3 min.
Opening eyes—1 min. Closing eyes—1 min.
Background recording 1 min.
Hyperventilation—3 min.
Background recording—5 min.
Opening eyes—1 min. Closing eyes—1 min.
Background recording 20 min.
Study repetition (up to 6 times)
Study Termination
Important!
When pathological activity appears in the record, the study is terminated as the main goal is achieved and the task is completed.
After the studies, the recording stops and the data are saved, which are transferred for analysis to the doctor, who forms the medical report.
5.3 VideoEEG monitoring from 4 hours (in children) to 9–12 hours in adults)
Purpose of the study: to evaluate changes in bioelectrical activity under conditions of a decrease in external stimuli and changes in the characteristics of the bioelectrical activity of the brain caused by a change in the phases of physiological sleep).
5.4 Patient preparation
The patient comes to the study in a calm state with a clean head. It is best that he does not attend work on the day of the study.
With him, the patient has pajamas or a tracksuit to change into.
Before the study, the patient is explained that he will be filmed by a video camera throughout the study and he will be in bed without a blanket.
Important!
The patient should not take sleeping pills for the onset of sleep, but the patient does not stop taking basic drugs (especially antiepileptic ones!)!
Conducting research
The patient is connected to the device as well as for routine examination; however, the use of electrically conductive gels is inappropriate for studies lasting more than 4 hours. When planning a long study, it is better to use a special conductive paste.
Important!
There is no need to require the subject to be in a state of sleep. A person can be in a state of passive relaxed wakefulness or perform normal activities. The main condition is constant video recording!
Important!
Functional stress tests, including opening-closing of the eyes, rhythmic photostimulation, and hyperventilation during sleep monitoring are NOT PERFORMED! Due to the possible disruption of the process of falling asleep.
All functional stress tests are carried out at the stage of a routine examination and an extended EEG examination!
During night sleep monitoring, the following events are noted:
Time of arrival of the patient in the ward
Bedtime
Light off time
Time of onset of sleep
Events (woke up, went to the toilet, etc.)
Main wake up time
Light on time
Time when the patient left the room.
After the studies, the recording stops and the data are saved, which are transferred for analysis to the doctor, who forms the medical report.
5.5 Ambulatory EEG monitoring (not always present in EEG laboratories!)
It is the longest version of the EEG—examination.
Purpose of the study: to establish how changes in the bioelectrical activity of the brain affect the daily life of the subject
The main task: to establish a direct relationship between the development of pathological bioelectrical activity and a violation of the quality of life of the subject.
Ambulatory EEG—monitoring is carried out using special mobile devices similar to ECG monitoring devices (Holter ECG).
The installation of electrodes should imply prolonged contact with the patient’s skin; therefore, special electrically conductive collodion-based adhesives are used as a contact medium. The use of standard gels for outpatient EEG monitoring is not suitable, and the use of conductive pastes is possible only within the daily study.
The time of the study is from 1 day to a week.
After installing the electrodes, they are connected to the device. The operator checks the charge of the power sources of the device, checks the fullness of the information storage, and controls the impedance. After these manipulations, the device is fixed on the patient’s body, eliminating tension and breakage of the conductors.
The subject is given a form of a diary of observations drawn up in a free form in which he must enter information about his current condition.
Important!
The main task of long-term EEG examinations is to PROVE THE DIRECT RELATIONSHIP of the functional disorders present in the subject with epileptic changes in bioelectrical activity or to prove the absence of this connection!
A successful examination is only one in which a functional disorder was recorded videographically, which forms the basis of the clinical picture of the disease and a clear connection was established between the fact of its occurrence and the registration of pathological paroxysmal activity on the electroencephalogram!!!
If there is no event registration or there is no direct connection between the clinical manifestations of the disease and changes in the electroencephalogram, the results of VideoEEG monitoring are not conclusive!
5.6 EEG examination in patients with stroke
Ischemic stroke is a disease that occurs as a result of cerebral infarction and is characterized by the development of persistent focal neurological syndromes of loss of functions, primarily motor.
Therefore, a functional study of the state of the bioelectrical activity of the brain under conditions of motor load is of great interest both in assessing the general condition and in developing rehabilitation measures.
The purpose of the study was to evaluate changes in the bioelectrical activity of the brain caused by violations of cerebral hemoperfusion and to identify the reactions of the microcirculatory vascular bed under conditions of physical exertion.
5.7 Periodization of ischemic stroke
the most acute period—the first 3 days (with regression of symptoms in the first 24 hours, a transient ischemic attack is diagnosed)
6. Mounting 25 active EEG electrodes (as element of “10-10” system)
Volumetric intracerebral processes are characterized by suppression of neuronal activity (especially in the early stages of development). On the EEG, this is reflected in the registration of slow-wave activity, which is poorly localized using the 10-20 system.
To address this issue, in 2017, the International Federation of Clinical Neurophysiology (IFCN) recommended a system of 25 active electrodes in a 10-10 electrode system as the research standard. This system includes 25 active electrodes, against 19 in the standard “10-20” system, which is achieved by introducing three pairs of additional electrodes F9–F10, T9–T10, P9–P10, which allow recording biopotentials from the basal parts of the brain.
6.1 Procedure for converting a “10-20” system to a “10-10” system
The procedure for converting the “10-20” system to the “10-10” system includes the introduction of six additional electrodes into the wiring diagram: F9 T9 P9 and F10 T10 P10, one row down (20% of the nasion-inion distance) from the F7 T3 T5 electrodes F8 T4 T6 (Table 1).
Device socket
Electrode
X1
F9
X2
F10
X3
T9
X4
T10
X5
P9
X6
P10
Table 1
Electrode connections accordingly, the device uses sockets.
Instrument socket Electrode X1 F9 X2 F10 X3 T9 X4 T10 X5 P9 X6 P10 For registration, an appropriate new mounting of electrodes is created (Figure 1).
Figure 1.
An example of creating a system 10-10 using additional channels of the device (Program “Neuron-Spectrum” LLC “Neurosoft,” Russia, author’s observation).
7. Features of the examination when using a multichannel EEG system
A traditional study with 21 scalp electrodes in a 10-20 system is carried out using simple electrode attachment systems, most often in the form of “caps” of intertwined elastic tubes or cords, and “bridge” electrodes, in which improved skin-electrode contact is achieved using physical solution. This is the so-called classical or “wet” EEG interface. Direct installation of electrodes on the scalp is also possible using needle electrodes or adhesive electrodes attached to the scalp with a paste or collodion gel. This system is used in cases of long recordings and sleep studies. In recent years, the “dry interface” system has been actively introduced, which does not require the use of conductive solutions, pastes, or gels. Each electrode of such a system has a chlorine-silver comb installed directly on the scalp, and the contact error is solved either by a larger electrode surface or by installing a signal microamplifier.
The classical EEG scenario represents a successive change in the recording of background activity and functional tests “on tape” or in one file, which allows the researcher to “scroll the record” to compare the characteristics of the bioelectrical activity of the brain under different conditions and under different external influences. Since the number of electrodes is small, and the distance between them is from 4 to 7 cm, then in such a system there are no strict requirements for determining the spatial location of each electrode.
However, the use of a multichannel system with more than 64 electrodes requires a more careful approach to creating a scalp-electrode system. A small distance between the electrodes of 1–2 cm requires careful use of solutions and gels, since with an overabundance of the latter, a common contact will occur between two adjacent electrodes and, accordingly, they will be “turned off” from the common recording system.
When using a 64-channel system, systems of ring electrodes pumped with an electrically conductive gel are more often used, but when using 128- and 256-channel systems, it is difficult to implement such a solution, since a large number of adjacent electrodes create the problem of forming “conductive bridges” and shorting adjacent electrodes to each other.
The next problem of the multichannel interface is the spatial localization of the electrodes. As mentioned earlier, the use of the 10-20 system and the use of visual-phenomenological analysis allow the researcher to do without this information or use the simplest methods of approximation by the area-electrode type. But the high-density system operates with a much larger number of electrodes located above the same zone, and the researcher uses various methods of analysis that require adequate consideration of differences and input data.
To solve this problem, both methods of a spherical model are currently used with the representation of the head as a sphere of a given radius with a uniform arrangement of electrodes on its surface, as well as more accurate methods of geodetic photogrammetry, which determines the position of the electrode from a series of spatial images with the construction of an individual three-dimensional model, or the method an electronic pointer that allows you to determine the position of the electrode and its connection with the brain structure obtained using the transformation of CT or MRI images (Figure 2).
Figure 2.
Spatial localization of 128 electrodes of a multichannel EEG system using a spherical head model (EEGLAB®, author’s observation).
8. Problems of visual representation of a multichannel EEG study
When trying to visually and phenomenologically analyze a multichannel EEG recording, it is difficult to identify individual diagnostically significant patterns, since a large amount of linear data is located in a limited space, so attempts to identify dynamic changes in bioelectrical activity under these conditions are doomed to failure in advance (Figure 3).
Figure 3.
Visual representation of native recording of 128 channels of EEG recording (EEGLAB®, author’s observation).
It is more rational to use mathematical processing of primary data with the presentation of results in the form of frequency graphs and amplitude-frequency maps (Figure 4) [13, 14].
Figure 4.
Mathematical analysis of the native recording, which allows to determine the area of desynchronization of the sensorimotor zone (EEGLAB®, author’s observation).
This approach makes it possible to identify functional changes in the bioelectrical activity of the brain by the type of potentials associated with the event, the use of a large number of electrodes that create a dense network allows not only to fix the response to the event, but also to see the reaction of adjacent cortical zones.
In the most acute and early recovery period, the patient’s condition is still unstable, because the cerebral blood supply system is being restructured, damaged as a result of occlusion of the cerebral arteries and the formation of a compensating collateral blood supply system.
Under these conditions, the determination of changes in the bioelectrical activity of the brain is directly related to disorders of cerebral microcirculation. Since the nerve cell does not have in its structure organelles containing a supply of nutrients, any change in the conditions of its blood supply leads to disturbances in the formation of action potential (AP) and postsynaptic potential (PSP), which is manifested by the appearance of slow-wave activity in the structure of the EEG recording.
To determine the change in the characteristics of bioelectrical activity, we will compare the state of passive relaxed wakefulness and physical activity in the form of rhythmic squeezing—unclenching the hands (Figure 5).
Figure 5.
The state of passive relaxed wakefulness in a patient with ischemic stroke in the basin of the left middle cerebral artery (EEGLAB®, author’s observation).
In a state of passive relaxed wakefulness, a zone of slow-wave activity of theta—range is recorded in the left frontotemporal leads. A preserved motor area in the right hemisphere of the brain and a shift in the focus of alpha activity to the undamaged hemisphere are determined (Figures 6 and 7).
Figure 6.
Formation of areas of low-frequency pathological activity in a patient who started the exercise test (EEGLAB®, author’s observation).
Figure 7.
Continued changes in the characteristics of bioelectrical activity by the end of 3 minutes of functional exercise testing (EEGLAB®, authors observation).
At the beginning of the load, a change in bioelectrical activity is observed, which is characterized by the appearance of a section of slow waves in the frontal regions of the right (intact) hemisphere of the brain, which is a reflection of the formation of a collateral flow along the system of the anterior communicating artery and the steal syndrome of the frontal regions of the healthy hemisphere.
At the third minute of the exercise test in the affected hemisphere, a pronounced increase in the area of slow-wave activity is observed, which characterizes pronounced microcirculation disorders due to decompensation of the collateral blood supply system. At the same time, the patient does not complain about the deterioration of the general condition.
This observation is important for the development of exercise programs at the early stages of medical rehabilitation, since, as shown above, even slight physical activity can cause decompensation of the emerging collateral blood supply system in such patients.
Conclusion (Report) is the main result of the study, which characterizes all its importance as a diagnostic method. The report is compiled by the medical specialist who conducted the study and should include the following sections:
Section 1 Guide containing.
Information of the referring physician (brief description of the patient’s condition)
Patient identification number in the clinic registration system
Age
Diagnosis
Neurological status
Treatment
Date of last seizure (in case of examination of a patient with epilepsy)
Clinical question of the attending physician to be answered by the study
Section 2. Technical
Information from EEG technician
Nr. EEG
Time and date of recording
Level of consciousness, wakefulness, cooperation with the patient
Activation procedures used in the study (photostimulation, hyperventilation, mental activation, sensory stimuli, etc.)
Section 3 Description
The description of the EEG is carried out using the terminology of the EEG glossary)
The use of special electrodes during application is noted (basal, nasal, and other additional, conditions for their attachment)
Recording conditions are indicated—wakefulness / sleep / stupor / coma
3.1. Background activity
Description of alpha—activity: severity, localization, distribution to the central and frontal leads, amplitude, frequency, frequency modality (monomodal, bimodal, polymodal) severity of amplitude modulations, interhemispheric asymmetry is or is not.
Description of beta activity, severity, localization, distribution to the posterior leads, amplitude, frequency, interhemispheric asymmetry, whether or not.
Slow activity Theta and Delta waves
Severity in leads, type, localization, formation of groups of waves, and pathological rhythms with indication of localization.
Paroxysmal activity if present
Appearance of non-epileptiform/epileptiform, bilaterally synchronous, focal, main pathological pattern, its amplitude, frequency, presence/absence of amplitude, and frequency gradients.
Special EEG patterns (if available)
3.2. Recording under stimulation conditions
The effect of the activation procedure (opening-closing the eyes)
Reaction to the test with photostimulation:
Rhythm learning yes/no, whether the test provokes the appearance of paroxysmal/epileptiform patterns in the recording. If they are present, a description of their amplitude, frequency, presence/absence of gradients in amplitude and frequency.
Response to hyperventilation
The time of the test is indicated (3, 5, 3+2 min, or the test is terminated at ... a minute).
Whether the trial induces paroxysmal/epileptiform patterns in the recording. If they are present, a description of their amplitude, frequency, presence/absence of gradients in amplitude and frequency.
Important
The normal hyperventilation response implies disorganization and flattening of rhythms for 1 minute of HB, as well as an increase in the index of slow waves in the theta range for 2–3 minutes conducting a sample on the index up to 40% of the epoch.
In children and adolescents, for 2–3 minutes of HB, high-amplitude paroxysmal bioelectrical activity may appear in the form of flashes of bilaterally synchronous waves of the alpha-theta-range, maximally expressed in amplitude in the fronto-central leads (the phenomenon of “respiratory waves” associated with functional immaturity mid-stem structures and their hypersensitivity to hypoxia).
Section 4. Final
In this section, the physician makes a judgment by interpreting the data obtained using clinical terminology. The interpretation of the results of the recording is carried out in the context of the diagnosis and the question of the referring physician (clinical significance of the results, prognosis, etc.) using general clinical terms; special EEG terminology should be avoided if possible.
10.2 Continued EEG study
Section 1 Guide containing.
Information of the referring physician (brief description of the patient’s condition)
Patient identification number in the clinic registration system
Age
Diagnosis
Neurological status
Treatment
Date of last seizure (in case of examination of a patient with epilepsy)
Clinical question of the attending physician to be answered by the study
Section 2. Technical
Information from EEG technician
Num. EEG
Time and date of recording
Level of consciousness, wakefulness, cooperation with the patient
Activation procedures used in the study (photostimulation, hyperventilation, mental activation, sensory stimuli, etc.)
Section 3 Description
The description of the EEG is carried out using the terminology of the EEG glossary)
The use of special electrodes during application is noted (basal, nasal, and other additional, conditions for their attachment)
Recording conditions are indicated—wakefulness / sleep / stupor / coma
3.1. Background activity
Description of alpha—activity: severity, localization, distribution to the central and frontal leads, amplitude, frequency, frequency modality (monomodal, bimodal, polymodal) severity of amplitude modulations, interhemispheric asymmetry is or is not.
Description of beta activity, severity, localization, distribution to the posterior leads, amplitude, frequency, interhemispheric asymmetry, whether or not.
Slow activity Theta and Delta waves
Severity in leads, type, localization, formation of groups of waves and pathological rhythms with indication of localization.
Paroxysmal activity if present
Appearance non-epileptiform/epileptiform, bilaterally synchronous, focal, main pathological pattern, its amplitude, frequency, presence/absence of amplitude, and frequency gradients.
Special EEG patterns (if available)
3.2. Recording under stimulation conditions
Important!
We note the number of stimulation tests in the study and the patient’s condition during their execution
3.2. The effect of the activation procedure (opening-closing the eyes)
Reaction to the test with photostimulation:
Rhythm learning yes/no, whether the test provokes the appearance of paroxysmal/epileptiform patterns in the recording. If they are present, a description of their amplitude, frequency, presence/absence of gradients in amplitude and frequency.
Response to hyperventilation
The time of the test is indicated (3, 5, 3+2 min, or the test is terminated at … a minute).
Whether the trial induces paroxysmal/epileptiform patterns in the recording. If they are present, a description of their amplitude, frequency, presence/absence of gradients in amplitude and frequency.
Important
The normal hyperventilation response implies disorganization and flattening of rhythms for 1 minute of HB, as well as an increase in the index of slow waves in the theta range for 2–3 minutes conducting a sample on the index up to 40% of the epoch.
In children and adolescents, for 2–3 minutes of HB, high-amplitude paroxysmal bioelectrical activity may appear in the form of flashes of bilaterally synchronous waves of the alpha-theta-range, maximally expressed in amplitude in the fronto-central leads (the phenomenon of “respiratory waves” associated with functional immaturity mid-stem structures and their hypersensitivity to hypoxia).
Important
If an epileptic seizure develops or the patient refuses to continue the procedure, stop the study
Section 4. Final
In this section, the physician makes a judgment by interpreting the data obtained using clinical terminology. The interpretation of the results of the recording is carried out in the context of the diagnosis and the question of the referring physician (clinical significance of the results, prognosis, etc.) using general clinical terms; special EEG terminology should be avoided if possible.
10.3 Video EEG monitoring
Section 1 Guide containing.
Information of the referring physician (brief description of the patient’s condition)
Patient identification number in the clinic registration system
Age
Diagnosis
Neurological status
Treatment
Date of last seizure (in case of examination of a patient with epilepsy)
Clinical question of the attending physician to be answered by the study
Section 2. Technical
Information from EEG technician
Num. EEG
Time and date of recording
Level of consciousness, wakefulness, cooperation with the patient
Time of arrival of the patient at the clinic
Time of arrival of the patient in the ward
Bed time
Light off time
Sleep time
Total sleep time
Number of awakenings
Light on time
Wake up time
Study termination time
Time of patient leaving the clinic
Section 3 Description
The description of the EEG is carried out using the terminology of the EEG glossary)
The use of special electrodes during application is noted (basal, nasal, and other additional, conditions for their attachment)
Recording conditions are specified
Awake
Sandman
NREM 1
NREM sleep phase 2
upon reaching
Stage 3 slow-wave sleep
4th phase of non-REM sleep
5 REM sleep
3.1. Waking with open eyes
The presence of oculograms and muscle artifacts is noted
3.2. Waking with closed eyes
Description of alpha activity: severity, localization, distribution to the central and frontal leads, amplitude, frequency, frequency modality (monomodal, bimodal, polymodal) severity of amplitude modulations, interhemispheric asymmetry is or is not.
Description of beta activity, severity, localization, distribution to the posterior leads, amplitude, frequency, interhemispheric asymmetry, whether or not.
Slow activity Theta and Delta waves
Severity in leads, type, localization, formation of groups of waves and pathological rhythms with indication of localization.
Paroxysmal activity if present
Appearance non-epileptiform/epileptiform, bilaterally synchronous, focal, main pathological pattern, its amplitude, frequency, presence/absence of amplitude and frequency gradients.
Special EEG patterns (if available)
3.3. Sandman
Flattening of rhythms is noted. The appearance of lambda waves in the occipital leads, oculographic artifact and myographic artifacts from shudders can be recorded.
The period of drowsiness can move into a state of passive relaxed wakefulness with eyes closed and can move into phase 1 of non-REM sleep.
3.4. 1 slow-wave sleep (non-REM I)
The flattening of rhythmic activity, characteristic of the state of drowsiness, persists. Lambda waves are absent in the frontal leads, a spindle-shaped sigma appears—a rhythm with a frequency of 16–22 Hz. Amplitude up to 30 microvolts.
Phase 1 slow-wave sleep can move into a state of passive relaxed wakefulness with eyes closed and can move into phase 2 slow-wave sleep.
3.4. NREM 2 (non-REM II)
The flattening of rhythmic activity is preserved. Lambda waves are absent in the frontal leads, a spindle-shaped sigma appears—a rhythm with a frequency of 16–22 Hz.
In the central-parietal leads, paroxysmal activity is recorded in the form of bilateral-synchronous polyphasic complexes with an amplitude of up to 100 microvolts (Vertex-potentials).
There is an increase in the index of theta range waves up to 30% in the recording epoch, the appearance of groups of theta waves.
2nd phase of non-REM sleep can go into a state of passive relaxed wakefulness with eyes closed and can go into phase 3 of slow-wave sleep.
3.5. NREM 3 (non-REM III)
There is an increase in the index of theta waves in the range of more than 30% in the recording epoch, the appearance of groups of theta waves and unstable rhythms. Bilaterally synchronous delta waves of high amplitude up to 40% are recorded in the recording epoch.
Sigma—the rhythm is not expressed, the vertex potentials are preserved, but the index is less than in the second phase of non-REM sleep.
NREM phase 3 can transition into NREM sleep 1 or 2.
3.6. 4 phase slow sleep (non-REM IV)
There is an increase in the delta wave index of more than 60% in the epoch. Delta activity is a bilaterally synchronous rhythm
Sigma—the rhythm is not expressed, the vertex potentials are not expressed.
NREM 4 can progress to NREM 3 or 2.
3.7. REM sleep phase (REM V)
Most often achieved in the second half of the night. It is characterized by flattening of background activity to the level of beta with the appearance of multiple oculographic artifacts of different directions. Vertex potentials and sigma rhythm are present but less pronounced than in the second phase of non-REM sleep
Important!
In each of the phases,
The type of brain activity characteristic of this phase.
Artifacts
Nonspecific and specific sleep phenomena
Paroxysmal and epileptiform changes, if any (indicating localization, amplitude and frequency)
10.4 Ambulatory monitoring
Section 1 Guide containing.
Information of the referring physician (brief description of the patient’s condition)
Patient identification number in the clinic registration system
Age
Diagnosis
Neurological status
Treatment
Date of last seizure (in case of examination of a patient with epilepsy)
Clinical question of the attending physician to be answered by the study
Section 2. Technical
Information from EEG technician
Num. EEG
Time and date of recording
Level of consciousness, wakefulness, cooperation with the patient
Time of arrival of the patient at the clinic
Machine start time
Total recording time (days)
Time of removal of the research apparatus
Time of patient leaving the clinic
Section 3 Description
The description of the EEG is carried out using the terminology of the EEG glossary)
The use of special electrodes during application is noted (basal, nasal, and other additional, conditions for their attachment)
Recording conditions are indicated in accordance with the diary entries of the subject
Assess the association of registered changes with disturbances in daily activities
When fixing epileptic seizures, their impact on the quality of life of the subject is assessed
Important!
With long-term outpatient monitoring, it is necessary to organize control over the state of electrode connection!
11. Conclusion
The study of the functional activity of the brain remains the most important problem in clinical neurophysiology. But for its solution, it requires the combined efforts of specialists from different areas of neuroscience and is unthinkable without the improvement of methods that make it possible to fix, localize, and understand the processes occurring in the nervous tissue.
The EEG method developed at the beginning of the twentieth century still retains its relevance in the clinic of neurological diseases. The main and most demanded advantage of the EEG method is the possibility of direct study of the bioelectrical activity of brain structures, which makes it possible to study processes with rapid dynamics occurring in brain structures.
Nevertheless, methodological approaches to the analysis of electroencephalograms need a thorough revision and the formation of a unified methodological approach to the implementation of research, especially with the active introduction of multichannel systems combined with computer signal processing into clinical practice, which in the future can change many ideas about the pathogenesis of various neurological diseases and suggest the most rational approaches to their therapy and rehabilitation.
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Written By
Sergey Alexander Gulyaev
Submitted: 14 October 2022Reviewed: 04 November 2022Published: 06 September 2023
Open access peer-reviewed chapter
