Electroencephalography (EEG) – How Does It Work?

Electroencephalography (EEG) was invented in 1924 by Hans Berger, and it represents a technique that measures the activity of the brain. It does so with electrodes that detect electrical impulses, and based on that, neurologists have learned a lot about how our nervous system works.

Our brains are one of the most complicated things in the universe, and scientists all over the world are trying their best to solve the puzzles of our minds. The focus wasn’t always on the brain, as ancient thinkers and philosophers believed that the heart is the moving force of the body and soul. It was only later on that the importance of the brain was recognized and the era of neuroscience began. 

Our central nervous system (CNS) is pretty much in charge of everything we do. Whether it is a simple hand movement, perception, and processing of the internal and external stimuli, or more complex thinking and planning, there isn’t a single thing you can do that doesn’t include your CNS. Your brain works all the time, and it is only during sleep when it takes some time to do a little maintenance, but your brain is still very active.

Since scientists have realized the importance of our nervous system, they have been working very hard to gain a little understating of it. The neuroscience has come a long way since its beginning and the first description of neuron in the 19th century, and today we know a lot about how our brain functions, and how it communicates with the rest of the body. However, there are still some mysteries. As it was profoundly put by the English philosopher Emerson Pugh: “If the human brain were so simple that we could understand it, we would be so simple that we couldn’t.” But that doesn’t mean we shouldn’t try. 

Electroencephalography (EEG) was invented in 1924 by Hans Berger, and it represents a technique that measures the activity of the brain. It does so with electrodes that detect electrical impulses, and based on that, neurologists have learned a lot about how our nervous system works.

Brief History of Electroencephalography

The brain exploration using EEG has been going on for almost a century. It is an excellent screening method that is directly linked to neural activity. It is based on the fact that neurons communicate using electrical current, and when many are firing at the same time, electrodes can detect those signals, and we can start to look for the occurring patterns. That is how we detected brain waves, which are described as oscillatory neural impulses.

It all started with the Italian scientists Luigi Galvani in the 18th century. He showed that the electrical impulses could be used to flex a frog’s hindquarters. The current would excite the nerves, which would lead to muscle contraction. That was the turning point in understanding neuroscience, as there is no science class today where they don’t show the experiment with the frog, and how the muscles can contract if the electric current is applied. A German physician and physiologist, Emil du Bois-Raymond expanded the knowledge about electricity and cells as he was the first to describe the fundamentals on which the nerves communicate, known as the action potential. That meant that the cells in our brain and body were not only able to send and receive chemical signals but the electric ones as well. This seems to be a faster way to send information, and neurons work mostly based on that.

All of these discoveries led to the beginning of the brain electrical recordings, similar to today’s EEG. They were done on animals by Richard Catton. He attached electrodes to the brain hemispheres and showed that the electrical impulses changed when the animal behavior was different. Unfortunately, his findings weren’t such a hit, but he did lay stage for what was coming. 

A German psychiatrist Hans Berger is considered a father of the EEG. He performed his first human experiment in 1924, and five years later, he published his findings and presented the technique in a form that is very similar to the way we do it today. By the mid 20th century, the EEG was already used to describe alpha and beta waves, and there were a lot of experiments looking into the effects of different drugs on the brain.

Today, the EEG is cheaper and easier to use than ever, and it is a useful diagnostic tool for many conditions like epilepsy, stroke, brain abnormalities, sleeping disorders, tumors, and more. 

Brain Waves

Different patterns of neural oscillations are called brain waves. They are detected and described by EEG readings and based on the state of mind and activity, there are several different types:

  • Beta waves can be detected while we are in the wake and active state. They occur when we are engaged in an activity, but interestingly, also when we observe other people’s actions.
  • Alpha waves are characteristics of wake but a deeply relaxed and calm state. People engaging in meditation are often experiencing them.
  • Theta waves happen mostly during the light stages of sleep. These transitional stages from wakefulness to deep slumber seem to have many benefits for our brains and bodies. It appears that this period of theta waves is connected to the integration of memory and that people who spend more time in the light stages of sleep have a higher ability to recall information.
  • Delta waves are the lowest in frequency, and they are reserved for the deepest, most restorative sleep. It is clear by now that scientists have described sleep architecture based on the different brain waves that occur during the night. Because of that, Stage 3 is also called deep, or delta wave sleep. It is essential for the proper functioning of the body and mind, and during this period our brain does the needed housekeeping, and our muscles are repaired.

Besides these four basic types, there are a few other brain waves described, as well as other neural occurrences. For instance, sleep spindles and K-complexes are both found in the light stages of sleep, and it appears that they play a crucial role in the embedding of new information into our heads.

Other than general activity, EEG can also interpret which areas of the cortex are responsible for processing a different kind of information at any given time. For instance, the occipital region is responsible for visual stimuli, so this area will be active during the screening if you are looking at a picture or flashing light. The parietal cortex is responsible for motor functions and processing information that is essential to us. The temporal region is responsible for speech production and language processing, while the frontal cortex makes up the most significant part, and it is essentially responsible for what keeps us human. It is accountable for our behavior, ability to plan, and it helps us maintain control and analytically think about ourselves and the world around us.

Why Would You Need an EEG?

This method is used to diagnose several brain disorders. For instance, if the epilepsy is present, there are rapid spiking waves during the seizure episodes. It can also be used to locate brain lesions, which can be a result of certain tumors or a stroke. EEG is used to diagnose any other disorders that may affect neural activity and brain waves, such as Alzheimer’s disease and some psychoses.

The EEG can be used to evaluate the brain damage caused by various traumas, drug intoxication, or comatose state. It can also be used to track the blood flow through the head during specific surgical procedures. Since we are mostly interested in the field of sleep, it is important to state that EEG is an essential tool at diagnosing different sleep disorders. That happens during the overnight study in a special facility, but more on that later.

If your medical provider has instructed you to take EEG, don’t worry, as this procedure is harmless and causes no discomfort. It is a non-invasive method, meaning that the electrodes don’t penetrate your skin, but rest on the outside of your head, and there is no risk of getting an electric shock. 

There are certain risks of having a seizure for people who are suffering from epilepsy. Due to the nature of these tests, you may have to breathe deeply and look at the flashing light, which can trigger these events in some people. However, don’t worry, as the technicians are fully trained and should contain the attack immediately. Other risks are mainly connected to the use of certain medications, and that is why you should always discuss that with a medical professional before taking the test. Other factors can interfere with the EEG results, and they include:

  • Low blood sugar levels caused by fasting
  • Bright or flashing lights
  • Drinking caffeine
  • Excess eye or body movement during the tests
  • Oily hair or the presence of hair products

How to Prepare For The EEG?

Your medical provider will usually talk you through all the preparation you need, but here is a list of things that you may be asked to do before the testing:

  • You will be given a consent form you need to sign to confirm that you are giving permission for the procedure. You should read it carefully, and ask questions if something doesn’t seem clear. Your medical provider should be happy to explain any details that might be confusing to you.
  • You must wash your hair the night before, or on the day of the procedure. Don’t use conditioner or the other hair products like gels or hairspray, as they can affect the results of the tests.
  • Talk to your medical provider about the medications and supplements that you are using. In most cases, they will advise you to continue with it, but in a few rare instances, they might direct you to stop using certain ones.
  • Avoid consuming any foods and drinks that contain caffeine for 8 to 12 hours before the procedure. That includes coffee, sodas, teas, and energy drinks.
  • Avoid fasting the day before the tests, as low blood sugar levels may influence the results.
  • If you are taking EEG as a part of the sleep study, your medical provider will probably tell you that you need to reduce your sleep during the night before the test. You are usually advised not to sleep for longer than 4 to 5 hours during that night. 
  • Based on your medical condition, your doctor may request other specific preparations, so be sure to discuss it with them.

What Does an EEG Look Like?

The procedure may vary based on your condition and the practices of your healthcare provider. But it usually looks something like this:

  • You will be asked to relax on a reclining chair or a bed, while the sleep technician measures your head and marks the places where he or she will attach the electrodes. They might scrub these spots with a special cream to remove any excess dead cells and improve the readings. 
  • After that, they will attach electrodes to your scalp using a special adhesive paste. Sometimes they use elastic caps fitted with electrodes instead. Wires go to the instrument that amplifies your brain waves, and then it’s all recorded on the computer. 
  • The test usually takes up to one hour, and during that time, you are supposed to stay motionless, relaxed, and with your eyes closed. The recording might be stopped from time to time, to let you re-adjust the position if you don’t feel comfortable. 
  • After the initial readings in your resting position, the sleeping technician may ask you to perform various tasks. They can instruct you to read a paragraph of text, look at a particular image, breathe deeply and rapidly, or look at the bright or flashing light. 

The video is taken during the whole process so that they can compare your movements with the readings to get more accurate results. If you are instructed to get an EEG as a part of your sleep study, it will look a bit different.

Overnight Sleep Studies

To detect any sleep disorders, your medical provider may instruct you to take an overnight sleep study called polysomnography. It is done in a special facility called a sleep clinic, where you will be subjected to a series of tests including the EEG.

Before the screenings, you will be instructed to keep a sleep diary for a week or two. There, you will note your everyday sleeping behaviors like the time you went to bed, the time you woke up, how long it took you to fall asleep, if you had any interruptions during the night, and how rested you felt the following day. All of this is important to the sleep specialists, as they can detect any behavior that can be causing sleep problems, and then adjust the tests accordingly. 

When you enter the sleep clinic, they will first ask you to fill several questionnaires that should include the Pittsburgh Sleep Quality Index and the Epworth Sleepiness Scale. These tests serve to measure the overall sleep quality, and if the final results pass a certain threshold, it indicates a possible presence of a sleep disorder.

Then, it’s the time for actual polysomnography. Sleep technicians will connect you to many devices that will monitor you while you are sleeping. They include EEG that measures your brain wave activity, as well as other machines that track your heart rate, breathing patterns, nocturnal eye and body movement, snoring, and more. The medical professionals will then combine these results with the tests you have taken beforehand to make the right diagnosis and prepare you for the next steps. 

Usually, the polysomnography lasts until the morning when you will be discharged from a sleep clinic until your results are done. In some cases, this overnight study is stopped in the middle of the night as the doctors are already ready to give the diagnosis. That is mostly in the case of sleep apnea, and then for the second part of the night, sleep technicians can hook you up to a positive air pressure machine that is the part of your treatment. This way, you get the diagnosis and the plan of treatment during the same night.

What Happens After The EEG?

After the procedure, doctors trained to analyze EEG will need to take a look at your reading. It usually takes a team of medical professionals to interpret the results and then send the information to the doctor that ordered these tests. Sometimes a neurologist can give you some basic data about your readings on the spot, right after the exam. But you will more often have to wait a few days for a report and detailed results.

A doctor can instruct some additional exams to the EEG, like the MRI head scan. That can give them more details about what is causing your problems if the EEG screenings are not sufficient. 

Based on the results and your medical condition, your healthcare provider will plan the next steps and the treatment plan. You shouldn’t be afraid to ask them anything about your health or treatment. Don’t hesitate to ask them to suggest some credible sources where you can read about the condition that is causing you problems, and learn more about it. Make sure to follow the treatment plan they prescribe you and give them the feedback on how successful it is so that they can adjust it if necessary.


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