Electroencephalogram Test on Alcoholics and Non Alcoholics

Electroencephalogram Test on Alcoholics and Non Alcoholics INTRODUCTION The electroencephalogram (EEG) is a measurement of the electrical activity in the patients brain. This electrical activity is produced by the firing of neurons (a nerve cell) within the brain and varies from patient to patient. In 1875, English physician Richard Caton discovered the presence of electrical activity in the brain; however, it was not until German neurologist Han Berger in 1924 used his ordinary radio equipment to amplify the brains electrical activity so he could record it on paper. He noticed that rhythmic changes in brain waves varied with the individuals state of consciousness (sleep, anesthesia, epilepsy) and that various regions of the brain do not emit the same brain wave frequency simultaneously. (http://www.bio-medical.com). The EEG was given its name by Berger who used the German term elektrenkephalogramm to describe the graphical representation of the electrical currents generated in the brain. The scientific community of Bergers time did not believe the concl usions he made and it took another five years until his conclusions could be verified through experimentation by Edgar Douglas Adrian and B.C.H Matthews. These experiments made head-waves and other scientists began studying the field and in 1936 W. Gray Walter demonstrated that this technology could be used to pinpoint a brain tumor. He used a large number of small electrodes that he pasted to the scalp and found that brain tumors caused areas of abnormal electrical activity. (Romanowski 1999) and http://www.ebme.co.uk. The brain is the central part of the nervous system, which is the most complicated system in the body. It is an intriguing organ that has been studied right from the time of brain development in the fetus. The human brain weighs about 1.5kg in adults. The cerebrum, which forms the bulk of the brain, is divided into two hemispheres, the right hemisphere and the left hemisphere. Each hemisphere of the brain interacts with one half of the body, but for unknown reasons, it is the right side that controls the left half of the body and the left half of the brain that controls the right half of the body. However, in most people, the left hemisphere of the brain is involved in language and creativeness, while the right side of the brain is more involved in understanding and judgment. The cerebrum, which is located in the forebrain, is the largest part of the human brain and is associated with higher brain functions such as thought and action. The cerebral cortex is divided into four sections called lobes. These include: the frontal lobe, parietal lobe, occipital lobe and temporal lobe. The frontal lobe is associated with reasoning, planning, parts of speech, movement and problem solving. The parietal lobe is associated with movement, orientation, recognition and perception of stimuli. The occipital lobe is associated with visual processing and the temporal lobe is associated with perception and recognition of auditory stimuli, memory and speech. (Khan 2009). Over the years with advancements in technology EEG electrodes, amplifiers and output devices were improved and scientists learned the best places to put the electrodes and how to diagnose its conditions. They also discovered how to create electrical maps to produce an image of the brains surface and today EEG machines have multiple channels, computer storage memories and specialized software that can create an electrical map of the brain. (Romanowski 1999). EEG has come a long way since its inception more than 100 years ago and it is used primarily in studying the properties of cerebral and neural networks in neurosciences (Michel et al. 2004). It is used to monitor the neurodevelopment and sleep patterns of infants in the intensive care unit and ultimately enable physicians to use the information to improve daily medical care (Scher 2004). The emergence of neurofeedback or EEG biofeedback has expanded the application of EEG for both cases with particular disorders or among healthy p articipants. EEG frequencies in neurofeedback can be controlled to influence certain cognitive performance and memory task, (Vernon et al. 2003). Interactive Brainwave Visual Analyzer (IBVA) is a form of biofeedback for the brain (neurofeedback). Its a training process of using technology to provide you with more information about what your body is doing than your ordinary senses provide. This feedback helps you learn to use your mind to develop greater control over your body, or, in the case of neurofeedback, your brain. IBVA detects brainwaves phasing at speeds measured in units of Hz for cycles per second between 0 and 60 Hz. It is used for sleep state and hypnosis analysis, image programming for sports training, super learning (photo reading) and for study. EEG biofeedback is effective in treating psychological disorders such as attention deficit, depression, chronic anxiety disorder, chronic alcoholics and neurological disorders like epilepsy. Patients with epilepsy that cannot be controlled by medication will often have surgery in order to remove the damaged tissue. The EEG plays an important role in localizing this tissue. Special electrodes can be inserted through the cortex or alternatively a grid of electrodes placed directly on the surface of the cortex. These recordings, often called Long Term Monitoring for Epilepsy (LTME), can be carried out for periods ranging from 24 hours to 1 week. The EEG recorded will indicate which areas of the brain should be surgically removed. (Smith n.d). Another important application of the EEG is used by anesthesiologist to monitor the depth of anesthesia. EEG measures taken during anesthesia exhibit stereotypic changes as anesthetic depth increases. These changes include complex patterns of loss of consciousness occurs (loss of responses to verbal commands and/or loss of righting reflex). As anesthetic depth increases from light surgical levels to deep anesthesia, the EEG exhibits disrupted rhythmic waveforms, high amplitude burst suppression activity, and finally, very low amplitude isoelectric or flat line activity. Quantitative EEG (QEEG) has come a long way in its relatively short life in terms of use in clinical practice. Now, as clinicians become aware of the scientific basis and power of using parametrically based measures of QEEG to assess an individual against age-matched populations, they find new ways to employ this technique. There are literally thousands of univariate electrophysiological measures that can be derived, transformed and normed into Z-scores (standard scores), to be used to indicate degrees of derivations from normal. QEEG offers a powerful application tool as a method for providing convergent evidence in the identification of clinical syndromes for individuals. Over the years, various clinicians using QEEG have attempted to establish brain maps to correspond with specific disorders such as learning disorders, attention deficit hyperactivity disorders (ADHD), chronic alcoholism and depression. While certain features may be associated with general types of impairments, the utilization of univariate sets of features have, to date, been unable to provide defining specific psychiatric disorders. Looking at only the univariate features without recognizing the full space of all deviant measures, one may not realize the particular cluster of measure that may contribute to specific disorders with distinct features. Multivariate statistical measurement sets encompass the space of regions by measurement, yielding distinctive complex patterns which yield greater sensitivity in discriminability. (Budzynski, Evans and Abarbanel 2008). The basic systems of an EEG machine include data collection, storage and display. The components of these systems include electrodes, connecting wires, a computer control module and a display device. The electrodes used can be either surface or needle electrodes. Needle electrodes provide greater signal clarity because they are injected directly into the body and this in turn eliminates signal muffling caused by the skin. Surface electrodes on the other hand are disposable models such as the tab, ring and bar electrodes as well as reusable disc and finger electrodes. These electrodes may also be combined into an electrode cap that is placed directly on the head (Romanowski 2002). EEG amplifiers convert weak signals from the brain into a more discernable signal for the output device. An amplifier may be set up as follows; a pair of electrodes detects the electrical signal from the body, wires connected to the electrodes transfer the signal to the first section of the amplifier (buffer amplifier). Here the signal is electronically stabilized and amplified by a factor of 5 10 and then next in line is a differential pre-amplifier that filters and amplifies the signal by a factor of 10 – 100. After passing through these amplifiers the signals are multiplied by hundreds or thousands of times. Multiple electrodes are used since the brain produces different signals at different points on the skull and the number of channels that an EEG machine has is related to the number of electrodes used. The amplifier is able to translate the different incoming signals and cancel out ones that are identical; this means that the output from the machine is actually the diff erence in electrical activity picked up by the two electrodes. This therefore means that the placement for each electrode is critical because the closer they are to each other the less differences in brainwaves will be recorded (Romanowski 2002). EEG SYSTEM LAYOUT (www.medicalengineer.com) Recording of the electrical activity in the brain takes place over a short period of time from where information is obtained from electrodes stationed at specific points on the patients head. Electrodes are placed on the scalp of the head usually after preparing the scalp area by light abrasion to reduce impedance due to dead skin cells. In order for the placement of these electrodes to be consistent throughout an internationally recognized method called the 10-20 System is followed. The 10 and the 20 gives the actual distances between adjacent electrodes. This distance can either be 10% or 20% of the total front-back or right-left distance of the skull, i.e. the nasion – inion and preauricular points respectively, http://www.neurocarelaunches.com. Specific measurements from bony landmarks (inion, nasion and preauricular point) are used to generate a system of lines, which run across the head and intersect at intervals of 10% or 20% of their total length as mentioned above. Th e standard set of electrodes consists of 21 recording electrodes and one ground electrode. The distance between the nasion and inion is measured along the midline and the frontopolar point, Fpz, is marked at 10% above the nasion. Frontal (Fz), central (Cz), parietal (Pz) and occipital (Oz) points are marked at intervals of 20% of the entire distance, leaving 10% for the interval between Oz and inion (see Diagram 1). The midline points Fpz and Oz routinely do not receive any electrode. The distance between two preauricular points across Cz is measured. Along this line, the transverse position for the central points C3 and C4 and the temporal points T3 and T4 are marked 20% and 40% respectively from the midline (see Diagram 2). The circumference of the head is measured form the occipital point (Oz) through temporal points T3 and T4 and the frontopolar point (Fpz). The longitudinal measurement for Fp1 is located on that circumference, 5% of the total length of the circumference to the left of Fpz. The longitudinal measurements for F7, T3, T5, O1, O2, T6, T4, F8 and Fp2 are at the distance of 10% of the circumference (see Diagram 3). An electrode is then placed on each of the two ear lobes. (Jasper 1958) and (Jasper 1983). In order for the EEG test to be a success and the best possible results obtained the preparation the patient must undergo is very basic since only a good night sleep before the test is needed along with a grease-free head on the morning of the test. However, it can get more technical should the patient be taking any medication and information on this medication must be passed on to the doctor. An EEG test may be done in a hospital or in a doctors office by an EEG technologist. Using the internationally recognized 10-20 system, the electrodes are placed on the patients head and the technologist can then put the patient through a variety of different tasks such as addition/subtraction of numbers, breathing deeply and rapidly or he can ask the person to wear a goggles sending out a strobe (bright flashing light). These tasks take place normally at 15-20 second durations with 30 second breaks in between. The electrodes attached to the patients head are connected by wires to a computer wh ich records the electrical activity in the brain. An EEG test can last between 1-2 hours and the results obtained from it can be read by a certified doctor known as a Neurologist. The results of an EEG test are in the form of waveforms which gives vital information about the patient. Waves can either be Alpha waves (frequency of 8 to 12 cycles per second), Beta waves (frequency of 14 to 50 cycles per second), Delta waves (frequency less than 5 cycles per second) or Theta waves (frequency of 4 to 7 cycles per second). Basic alpha waves, which originate in the cortex, can be recorded if the patient closes his eyes and put his brain at rest as much as possible. Beta activity is a normal activity present when the eyes are open or closed. It tends to be seen in the channels recorded from the centre or front of the head. Some drugs however, tend to increase the amount of beta activity in the EEG. Theta activity can be classified as both a normal and abnormal activity depending on the age and state of the patient. In adults it is normal if the patient is drowsy. However, it can also indicate brain dysfunction if it is seen in a patient who is alert and awake. In youn ger patients, theta activity may be the main activity seen in channels recorded from the back and central areas of the head. Delta activity is only normal in an adult patient if they are in a moderate to deep sleep. If it is seen at any other time it would indicate brain dysfunction. Abnormal activity may be seen in all or some channels depending on the underlying brain problem. The stroke or blow on the head. (Niedermeyer, Ernest and Lopes da Silva 2004). ALPHA WAVES BETA WAVES THETA WAVES DELTA WAVES (http://www.electropsychology.com) Each type of wave mentioned above gives us information about the patient, for example in a normal patient we tend to observe mainly alpha or beta waves since both sides of the brain show similar patterns of electrical activity. A normal person in this case is described as one who doesnt possess any of the following diseases or injuries; head injury, neurological disease, convulsions, drug abuse, alcohol abuse, memory difficulties, confusion, depression, delusions/hallucinations and learning disabilities. If the patient is abnormal you may find two sides of the brain giving different electrical activities and this may mean there is a problem in one side of the brain caused by a brain tumor, stroke, infection or epilepsy. EPILEPTIC SPIKES AND WAVE DISCHARGES MONITORED WITH EEG (http://www.webmd.com). A stroke, which is a sudden disruption in blood flow to brain, caused by blockage or bleeding of a blood vessel and Epilepsy which is a nervous system disorder, can cause abnormal electrical activity in the brain and this abnormality can be seen from the results of an EEG test. Another common disease which is on the escalation presently is Alcoholism. This disease is known as alcohol dependence syndrome i.e. the most severe stage of a group of drinking problems, and the person who has this disease is known as an alcoholic. Alcohol clearly affects the brain since impairments such as difficulty in walking, blurred vision, slurred speech, slowed reaction times and impaired memory are detectable after only one or two drinks and is quickly resolved when drinking stops. We do know that heavy drinking may have extensive and far-reaching effects on the brain ranging from simple slips in memory to permanent and debilitating conditions that require lifetime custodial care (White 2003). Accordi ng to the number 1 website for alcoholism, http://www.alcoholism.about.com, studies have shown that brains of alcoholics are smaller, lighter and shrunken when compared to that of a normal person. The cerebral cortex or gray matter in the brain controls all the complex mental activities and this is filled with neurons connected by single long fibers which make up the hard wiring of the brain. Heavy consumption of alcohol is particularly damaging on this hard wiring hence the reason why the brain becomes lighter and smaller and the alcoholic severe impairments. SCHEMATIC DRAWING OF THE HUMAN BRAIN, SHOWING REGIONS VULNERABLE TO ALCOHOLISM-RELATED ABNORMALITIES. (http://www.elvizy.com). Another major organ apart from the brain which alcohol affects is the liver. Long-term abusers of alcohol usually have some degree of liver damage, ranging in severity from asymptomatic and reversible fatty liver, through hepatitis and cirrhosis, to primary liver cell carcinoma, which is usually fatal. Evidence is accruing to suggest that this spectrum of disorders may be a progressive series of stages of increasing severity. Alcohol liver damage accounts for the vast majority of cases of cirrhosis in patients coming to autopsy. Further, mortality from cirrhosis is associated with national per capita levels of consumption. In North-American studies, alcoholic cirrhosis was one of the top five causes of mortality for people aged 25 to 64 years in the 1960s and 1970s. In 1992, Savolainen, Penttila and Karhunen investigated the relationship between alcohol intake and liver cirrhosis in Finland, where the per capita consumption rates doubles between 1969 and 1974. Rates of liver cirrhosi s mortality rose from 4.2 to 9.7 per 100,000 between 1968 and 1988. The mortality rate from cirrhosis has been estimated as between seven and thirteen times higher in alcoholics than in those who do not drink. Although it is more common in men than in women, there is evidence that liver disease progresses more rapidly in the female alcohol abuser (Knight and Longmore 1996). Alcoholics, they say, are not like helpless victims of measles or cancer. They may have impaired control but they can gain control through will-power and learning certain techniques. While the cause of alcoholism is unknown, a number of risk factors have been identified. These include; availability (Australian Aborigines illustrate the importance of availability of alcohol as a risk factor since when they were forbidden to drink there apparently was a low rate of alcohol abuse), family history (alcoholism in the family is probably the strongest predictor of alcoholism occurring in particular individuals), sex (st udies have confirmed higher incidence of alcoholism in men than in women), age (alcoholism in men usually develops in the teens, twenties and thirties while in women it often develops later), geography (people living in urban or suburban areas are more often alcoholics than those living in farms or in small towns), occupation (waiters, bartenders, Dockers, musicians, authors and reporters have relatively high cirrhosis rates whereas accountants, postmen and carpenters have relatively low rates), religion (almost all Jews and Episcopalians drink, but alcoholism among Jews is uncommon and appear relatively low among Episcopalians, whereas Irish Catholics in the USA and UK have high rates of alcoholism) and school difficulty ( secondary school dropouts have a record of being irritable and melancholy and experience feelings of guilt and remorse which drives them to become alcoholics. These lose interest in life and contemplate suicide which is a common outcome of alcoholism). People who have been drinking large amounts of alcohol for long periods of time run the risk of developing serious and persistent changes in the brain. Damage may be as a result of the alcohol on the brain or may result indirectly, from a poor health status or from severe liver disease (Goodwin 2000). Alcoholics are not all alike since they experience different degrees of impairment and the disease has different origins for different people. Consequently, researchers have not found conclusive evidence that any one variable is solely responsible for the brain deficits found in alcoholics. Characterizing what makes some alcoholics vulnerable to brain damage whereas others are not remains the subject of active research. The good news is that most alcoholics with cognitive impairment show at least some improvement in brain structure and functioning within a year of abstinence, though some people take much longer (Bates, Bowden and Barry 2002), (Gansler 2000) and (Sullivan 2000). Clinicians must consider a variety of treatment methods to help people stop drinking and to recover from alcohol related brain impairments, and tailor these treatments to the individual patient. Development of these therapies would occur over time with advancements in technology. Brain imaging techniques are u sed by medical doctors so that they can monitor the course of these therapies and see how successful they are. This monitoring is important since imaging can reveal information such as structural, functional and biochemical changes in the living patient over a period of time. Promising new medications also are in the early stages of development, as researchers strive to design therapies that can help prevent alcohols harmful effects and promote the growth of new brain cells to take the place of those that have been damaged by alcohol. OBJECTIVES Electroencephalogram or EEG is a tool used to image the brain while it is performing a cognitive task. This allows us to detect the location and magnitude of brain activity involved in the various types of cognitive functions we study. EEG allows us to view and record the changes in your brain activity during the time you are performing the task. Results from an EEG is extremely useful since Neurologists use this to diagnose seizure disorders (epilepsy), brain tumors, brain hemorrhage, cerebral infarct, head injury, sleep disorders and in confirming death in someone who is in a coma. (Tatum 2007). In this research project we have narrowed the study of the EEG to examine male alcoholic and non-alcoholic patients. The general objective of this project requires us to compare EEG results obtained from testing alcoholic and non-alcoholic patients at the Eric Williams Medical Sciences Complex. An alcoholic is one who suffers from the disease known as alcoholism and cannot control how much they consume. Identification of one involves an objective assessment regarding the damage that imbibing alcohol does to the drinkers life compared with the subjective benefits the drinker perceives from consuming alcohol. While there are many cases where an alcoholics life has been significantly and obviously damaged, there are always borderline cases that can be difficult to classify. Apart from the general objective of this research project there were many smaller tasks which had to be completed in order for us to obtain successful results and hence fulfill our main objective. The first task of this research project entailed sourcing alcoholic and non-alcoholic volunteers to test. This was particularly important since the successfulness of this task would revolve solely around our general objective. However, once this first task was sorted out and patients were tested, from the results obtained we used analytical methods such as monopolar absolute power maps, coherence maps and chaos analysis to help us get a clearer illustration of the results and hence make the general objective much clearer. The second objective of this project required us to have sufficient background information on the EEG, the experimental methodology when conducting an EEG (10-20 System), analytical methods used to illustrate EEG results, alcoholism, EEG on alcoholics and other general topics revolving around the area of research. In order for this to be a success the necessary books, journals, websites had to be sourced and read before any practical work commenced. Once these two tasks were performed successfully, we then set out to obtain our general objective of analyzing and comparing EEG results of both alcoholics and non-alcoholics. LITERATURE REVIEW An electroencephalogram (EEG) is a test that measures and records the electrical activity of your brain by using surface biopotential electrodes. These electrodes are attached to the patients head and hooked by wires to a computer which records the brains electrical activity on the screen or on paper as wavy lines (waveforms). Among the basic waveforms are the alpha, beta, theta and delta rhythms. Alpha waves occur at a frequency of 8 to 12 cycles per second in a regular rhythm and are present only when you are awake but have your eyes closed. They normally disappear when you open your eyes or start concentrating mentally. Beta waves occur at a frequency of 13 to 30 cycles per second and are usually associated with the use of sedative medications. Theta waves occur at a frequency of 4 to 7 cycles per second and are most common in children and young adults. Delta waves occur at a frequency of 0.5 to 3.5 cycles per second and generally occur in young children or during deep sleep. Duri ng an EEG, typically about 20-30 minutes of activity are evaluated and special attention is paid to the basic waveforms, but brief bursts of energy and responses to stimuli, such as light are also examined, (The university of Texas medical branch, http://www.utmbhealthcare.org). Results from an EEG test can tell a lot about the patient and is a read by a neurologist. The waves recorded can be classified as normal or abnormal. Abnormal waves can indicate medical problems, whereas different types of normal waves can indicate various states or activity levels. The value of understanding the normal EEG lies in developing the foundation to provide a clinical basis for identifying abnormality. Knowledge of normal waveform variations, variants of normal EEG that are of uncertain significance, and fluctuations of normal EEG throughout the lifecycle from youth to the aged are essential to provide an accurate impression for clinical interpretation. When abnormality is in doubt, a conservation impression of normal is proper. EEG produces a graphic display of a difference in voltages from two sites of brain functions recorded over time. Extra cranial EEG provides a broad survey of the electrocerebral activity throughout both hemispheres of the brain while intracranial E EG provides focused EEG recording directly from the brain through surgically implanted electrodes that are targeted at specific regions of the brain. (Tatum 2007). Information about a diffuse or focal cerebral dysfunction, the presence of interictal epileptiform discharges (IEDs), or patterns of special significance may be revealed from an abnormal EEG. For the successful interpretation of an abnormal EEG, one must first understand the criteria necessary to define normal patterns. While a normal EEG does not exclude a clinical diagnosis (i.e. epilepsy), an abnormal finding on an EEG may be supportive of a diagnosis (i.e. in epilepsy), be indicative of cerebral dysfunction (i.e. focal or generalized slowing), or have nothing to do with the reason that the study was performed (i.e. in headache). It is in the clinical application of the EEG findings that imparts the utility of EEG. (Tatum 2007). Two important applications involving EEG wave classification are diagnosis of sleep disorde rs and construction of brain-computer interfaces to assist disabled people with daily living tasks. Sleep occupies roughly one-third of a persons life and is indispensable for health and well-being. Sleep apnea is a disorder characterized by a ten-second or longer pauses in breathing during sleep. A person with sleep apnea cannot self-diagnose the presence of this disorder so in order to make diagnoses for sleep disorders, physicians usually need to study patients sleep patterns through sleep recording. A typical sleep recording has multiple channels of EEG waves coming from the electrodes placed on the subjects head. The waves from a healthy subject are stable about zero and show relatively high variability and low correlation whilst the waves from a person with sleep difficulty show less variability and higher correlation. Measuring EEG signals is a non-intrusive procedure since it does not cause any pain to the subject. Sleep staging is the pattern recognition task of classifying sleep recordings into sleep stages continuously over time and is performed by a sleep stager. These sleep stages include rapid-eye movement (REM) sleep, four levels of non-REM sleep and being awake. Sleep staging is crucial for the diagnosis and treatment of various sleep disorders. In order to make many EEG-based applications practical enough for routine use, it is necessary to achieve high accuracy in EEG wave classification. For physicians specializing in sleep disorders, improving sleep stage classification accuracy can increase both their diagnostic accuracy and the speed with which they make diagnosis. (Min and Luo. n.d). DIAGRAM SHOWING EEG SLEEP PATTERNS, (http://www.benbest.com) Brain-Computer interfaces (BCIs) are currently being developed to facilitate the control of computers by people who are disabled. As disabled people think about what they want to have the computer do, their thinking is classified based on their EEG waves and corresponding instructions are automatically executed by the computer. Accurate EEG wave classification is a critical requirement for computers to receive correct instructions. There are various kinds of BCIs with the most promising one being the P300 BCI using EEG signals. This is so because of its non-invasiveness, ease of use, portability and low set-up cost. In neuroscience, P300 refers to a neutrally-evoked potential component of EEG. (Min and Luo. n.d). Quantitative EEG signal analysis involves the transformation of the EEG signal into numerical values that can be used to examine selected EEG features. Once a specific feature of the EEG has been quantified, it can be displayed using various graphical methods such as topographic mapping or spectral trend monitoring. Other applications of quantitative analysis include automated event detection, intraoperative or ICU monitoring, and source localization. Normative databases of quantitative EEG features (such as the peak alpha rhyth m frequency or amount of alpha reactivity) can be used for statistical comparisons in research studies. Statistical quantitative EEG analysis is not yet considered reliable as an independent measure of abnormal brain function for clinical purposes. Topographic mapping refers to the graphical display of the distribution of a particular EEG feature over the scalp or cortical surface. Advanced forms of topographic mapping attempt to display EEG activity as it might be seen at the cortical surface by superimposing a color or gray scale image of the EEG feature onto the cortical surface image taken from the subjects MRI. More simplified forms of topographic mapping create a graphic display of an EEG feature over an imaginary head surface. All methods of topographic mapping depend heavily on montage construction. (Fisch and Spehlmann 1999). DIAGRAM SHOWING AN EEG TOPOGRAPHIC MAP, (http://www.cerebromente.org) Automated event detection is a form of quantitative analysis in which certain signal characteristics are used to classify an EEG change. It is most commonly applied to the detection of electrographic seizures during epilepsy monitoring. Intraoperative EEG monitoring is performed using continuous routine EEG visual inspection alone or in combination with quantitative EEG monitoring. The most common application of intraoperative EEG monitoring is for ca