- Sleeping While Awake
- Local Slumber
- Wake up: You’re fooling yourself about sleep, study says
- 1. Adults need five or fewer hours of sleep
- 2. It’s healthy to be able to fall asleep ‘anywhere, anytime’
- 3. Your brain and body can adapt to less sleep
- 4. Snoring, although annoying, is mostly harmless
- 5. Drinking alcohol before bed helps you fall sleep
- 6. Not sleeping? Stay in bed with eyes closed and try and try
- 7. It doesn’t matter what time of day you sleep
- 8. Watching TV in bed helps you relax
- 9. Hitting snooze is great! No need to get up right away
- 10. Remembering your dreams is a sign of good sleep
- More myths
- Medscape Log In
- Sleep – Digg
- EEG tests and epilepsy
- What does an EEG test do?
- What information does an EEG test give?
- Can an EEG test show what type of seizures I have?
- Can an EEG test show if there is any damage in my brain?
- Will an EEG test cause me to have a seizure?
- Will I have to give my consent (permission) for an EEG test to be done?
- Will having a seizure during an EEG test affect my right to drive?
- Will I have to have more than one EEG test?
- Standard EEG tests
- Sleep EEG tests
- Sleep-deprived EEG tests
- Ambulatory EEG tests
- Hospital video-telemetry
- Home video-telemetry
- Invasive EEG-telemetry
Sleeping While Awake
“It was literally true: I was going through life asleep. My body had no more feeling than a drowned corpse. My very existence, my life in the world, seemed a hallucination. A strong wind would make me think my body was about to be blown to the end of the earth, to some land I had never seen or heard of, where my mind and body would separate forever.”
—From Sleep, by Haruki Murakami, 1989
We've all been there. You go to bed, close your eyes, blanket your mind and wait for consciousness to fade. A timeless interval later, you wake up, refreshed and ready to face the challenges of a new day (note how you can never catch yourself in the act of losing consciousness!). But sometimes your inner world does not turn off—your mind remains hypervigilant.
You toss and turn but can't find the blessed relief of sleep. The reasons for sleeplessness may be many, but the consequences are always the same: You are fatigued the following day, you feel sleepy, you nap. Attention wanders, your reaction time slows, you have less cognitive-emotional control. Fortunately, fatigue is reversible and disappears after a night or two of solid sleep.
We spend about one third of our lives in a state of repose, defined by relative behavioral immobility and reduced responsiveness to external stimuli. Cumulatively, this amounts to several decades' worth of sleep over the lifetime of an average person.
Ah, I know you're thinking, Wouldn't it be great if we cut down on this “wasted” time to be able to do more! When I was younger, I, too, lived by the motto “You can sleep when you're dead.
” But I've woken up to the fact that for optimal, long-term physical and mental health, we need sleep.
Humans share this need for daily sleep with all multicellular creatures, as anybody growing up with dogs, cats or other pets knows.
An understanding of sleep's importance can be observed by contemplating the biological process itself.
Sleep is homeostatically regulated with exquisite precision: pressure to go to sleep builds up during the day until we feel sleepy in the evening, yawn continuously and nod off.
If deprived of sleep, humans experience an ultimately irresistible need to seek repose—they, in fact, become “sleep drunk.” An older, 19th-century term, closer to the truth, is “cerebral exhaustion,” the brain demanding its rest.
In my last Consciousness Redux column, I described how clinicians define sleep by recording brain waves from a net of electroencephalogram (EEG) sensors placed on the scalp of the sleeper [see photograph below].
the surface of the sea, the electrical brain is ceaselessly in commotion, reflecting the unseen, tiny tremors in the cerebral cortex underneath the skull that are picked up by the EEG electrodes.
Rapid eye movement (REM) sleep is characterized by low-voltage, choppy, swiftly changing brain waves (paradoxically, also typical of relaxed wakefulness), whereas non-REM sleep is marked by slowly rising and falling waves of larger amplitude.
Indeed, the deeper and more restful the sleep, the slower and larger the waves that reflect the brain's idling, restorative activity. These voltage oscillations, referred to as delta waves, can be as slow as once every four seconds and as fast as four times a second (that is, in the 0.
25- to four-hertz frequency range). Tuning into the discharge of individual neurons during deep sleep reveals discrete off periods, when nerve cells cease generating any electrical activity for 300 to 400 milliseconds. Such recurring silent periods, synchronized across large parts of the cortex, are the cellular hallmark of deep sleep.
My last column, “To Sleep with Half a Brain,” highlighted the growing realization of sleep researchers that being awake and asleep are not all-or-none phenomena. Just because you're asleep doesn't necessarily imply that your entire brain is asleep. Conversely, as I will describe now, we have also learned that even when you're awake, your entire brain may not be awake.
A case in point for sleep intruding into wakefulness involves brief episodes of sleep known as microsleep.
These intervals can occur during any monotonous task, whether driving long distances across the country, listening to a speaker droning on or attending yet another never-ending departmental meeting.
You're drowsy, your eyes get droopy, the eyelids close, your head repeatedly nods up and down and then snaps up: your consciousness lapses.
The author, his head clad in a dense net of EEG sensors, participates in a sleep study in the laboratory of Chiara Cirelli and Giulio Tononi at the University of Wisconsin–Madison. Credit: CHRISTOF KOCH
In one experiment attempting to explore this condition, participants had to track a randomly moving target on a computer monitor with a joystick for 50 minutes. While straightforward, this visuomotor task demands nonstop attention that becomes difficult to sustain after a while.
Indeed, on average, participants had 79 microsleep episodes per hour, lasting between 1.1 and 6.3 seconds apiece, with an attendant drop in performance.
Microsleep shows up in the EEG record by a downward shift from activity dominated by the alpha band (8 to 13 Hz range) to oscillations in the theta band (4 to 7 Hz).
Perniciously, subjects typically believe themselves to be alert all the time during microsleep without recalling any period of unconsciousness. This misapprehension can be perilous to someone in the driver's seat.
Microsleep can be fatal when driving or operating machinery such as trains or airplanes, hour after tedious hour.
During a microsleep episode, the entire brain briefly falls asleep, raising the question of whether bits and pieces of the brain can go to sleep by themselves, without the entire organ succumbing to slumber.
Indeed, Italian-born neuroscientists Chiara Cirelli and Giulio Tononi, who study sleep and consciousness at the University of Wisconsin–Madison, discovered “sleepy neurons” in experimental animals that showed no behavioral manifestation of sleep. In this research, 11 adult rats had microwires implanted into their frontal motor cortex, which controls movement.
Inserted into the cortical tissue, the sensors picked up both the voltage called the local field potential (LFP), akin to the EEG, in addition to the spiking activity of nearby nerve cells.
As expected, when awake, the LFP was dominated by low-amplitude, fast waves readily distinguishable from the larger and slower waves characteristic of non-REM deep sleep [see box below].
At the level of individual neurons, the awake animals' cortical cells chatted away in an irregular, staccato manner over an extended period.
Conversely, during deep sleep, cortical neurons experienced pronounced “on” periods of neural activity and “off” times during which they are silent. This neuronal reticence occurs simultaneously all over the cortex.
It alternates with regular on periods, leading to the rising and falling brain waves that are the hallmark of deep sleep.
Knowing all this, the researchers decided to probe further.
Instead of letting the rats go to sleep at their usual bedtime, the experimentalists engaged the animals in a rodent version of late-night video gaming, continuously exposing them to toys and other objects to sniff, explore and play with.
They tapped on the cage and otherwise prevented them from assuming a sleep posture or becoming drowsy. After four hours of such excitement, the rats could finally slumber.
As expected from previous animal and human studies, by the end of the sleep deprivation phase, the LFP began to shift to lower frequencies, compatible with the idea that the pressure for the animals to sleep steadily built up.
Closer inspection of the electrical signatures, however, revealed something unexpected: occasional, sporadic, silent periods of all or most of the neurons in the recorded brain region [see box below] without the animals showing either behavioral or EEG manifestations of microsleep.
These short, off- episodes were often associated with slow waves in the LFP. The opposite happened during recovery sleep, toward the end of this six-hour period, when the pressure to sleep had presumably abated.
At this point, large and slow waves in the LFP became more infrequent, and neuronal activity turned more irregular, as it did during wakefulness.
It appears that when awake but sleep-deprived, neurons show signs of sleepiness, whereas after hours of solid sleep, individual neurons start waking up. Careful statistical analysis confirmed these trends: the number of off periods increased during the four hours the rats were forced to stay awake, and the opposite dynamic occurred during recovery sleep.
One question was whether any one neuron fell asleep independent of any other neuron. Or was this occurrence more of a global phenomenon, whereby all neurons simultaneously transition to an off period? The answer, obtained by implanting a second array of microwires into a second cortical region—the parietal cortex, a quite distinct region from the motor cortex—was “yes” to both questions.
Click or tap to enlarge
Credit: “LOCAL SLEEP IN AWAKE RATS,” BY VLADYSLAV V. VYAZOVSKIY ET AL., IN NATURE, VOL. 472; April 28, 2011
That is, sometimes neurons in both regions went off together, whereas at other times they did so independently.
Yet as the sleep pressure built up, after several hours of being kept awake, neuronal activity during sleep deprivation did become more globally synchronized (as it does in deep sleep).
wise, the longer the animal slept during the recovery period, the less ly slow waves were simultaneously detected at both cortical sites. Groups of neurons can be more easily recruited to produce the slow oscillations that constitute deep sleep when sleep pressure is high.
These results paint a more nuanced view of wakefulness and sleep than the prevailing one, in which both conditions were considered to be global, all-or-none states of consciousness.
Instead these data, buttressed by single-neuron recordings from patients with implanted microelectrodes, as used occasionally in epilepsy treatment, suggest that even when the subject is awake, the individual's neurons can become tired and occasionally check out.
The heavier the sleep pressure, the more ly this will happen simultaneously at many places in cortex. Conversely, after many hours of restful sleep, some of these neurons become decoupled from these brain-wide oscillations and begin to wake up.
But with neurons going off-line during sleep deprivation, shouldn't there be some deterioration in performance? After all, these neurons must serve some purpose, and if they drowse, something ought to suffer.
To investigate this question, Cirelli, Tononi and their collaborators trained the rats to reach with one of their front paws through a narrow opening to grasp a sugar pellet on a shelf.
If done clumsily, the pellet falls off and cannot be retrieved anymore.
Learning this task engages a particular sector of the motor cortex that undergoes change as a consequence of training.
Trawling for off periods while the animal reaches out for the sweets, the investigators found these gaps in neuronal firing are more ly to occur in the motor cortex a fraction of a second before a failed attempt to grab the pellet as compared with when the rat successfully picked up a sweet treat.
Indeed, the occurrence of a single off period lowered the odds of a successful trial by more than a third. These effects were restricted to the motor cortex and were not seen in the parietal cortex, which is not engaged by the reaching task. As the animals became more sleep-deprived, their overall performance suffered, as is typical for sleep-deprived humans.
What this study discovered is the existence of local sleep during sleep deprivation: isolated cortical groups of neurons that briefly go off-line while the animal, to all outward appearances, continues to move about and do what it does. Local shut-eye is more ly to occur if those neurons are actively engaged, as they are when learning to grab a sugar pellet. Neurons, too, become tired and disengaged, a microcosm of what happens to the whole organism.
Extrapolating from these data, it seems plausible that as the pressure for sleep increases, the frequency of these off events and their preponderance in the cortex increase until activity in the entire brain becomes suddenly but briefly synchronized and the brain falls into deep sleep—the eyes close, and the head nods. The subject enters microsleep.
Sleep is a fascinating subject, even though we cannot knowingly experience deep sleep, because our consciousness is switched off. Sleep is a finely regulated aspect of our brain's daily cycle as the sun rises and sets, a state whose function remains controversial.
Over the past century clinicians and neuroscientists have discovered different sleep phases (rapid eye and nonrapid eye movements) and the distinct regions of the midbrain and brain stem involved in controlling them. What is more, these researchers have demystified narcolepsy, when patients abruptly and irresistibly fall asleep, microsleep and now local sleep. What will come next?
Wake up: You’re fooling yourself about sleep, study says
Hey, sleepyheads. What you believe about sleep may be nothing but a pipe dream.
Many of us have notions about sleep that have little basis in fact and may even be harmful to our health, according to researchers at NYU Langone Health’s School of Medicine, who conducted a study published Tuesday in the journal Sleep Health.
“There’s such a link between good sleep and our waking success,” said lead study investigator Rebecca Robbins, a postdoctoral research fellow in the Department of Population Health at NYU Langone Health. “And yet we often find ourselves debunking myths, whether it’s to news outlets, friends, family or a patient.”
Robbins and her colleagues combed through 8,000 websites to discover what we thought we knew about healthy sleep habits and then presented those beliefs to a hand-picked team of sleep medicine experts. They determined which were myths and then ranked them by degree of falsehood and importance to health.
Here are 10 very wrong, unhealthy assumptions we often make about sleep, an act in which we spend an estimated third of our lives — or, if we lived to 100, about 12,227 combined days.
Stop yawning. It’s time to put these unsound sleep myths to bed.
1. Adults need five or fewer hours of sleep
“If you wanted to have the ability to function at your best during the day, not to be sick, to be mentally strong, to be able to have the lifestyle that you would enjoy, how many hours do you have to sleep?” asked senior study investigator Girardin Jean-Louis, a professor in the Department of Population Health.
“It turns out a lot of people felt less than five hours of sleep a night was just fine,” he said. “That’s the most problematic assumption we found.”
We’re supposed to get between seven and 10 hours of sleep each night, depending on our age, but the US Centers for Disease Control and Prevention says that a third of Americans sleep fewer than seven hours a night. According to World Sleep Day statistics, sleep deprivation is threatening the health of up to 45% of the global population.
“We have extensive evidence to show that sleeping five hours a night or less, consistently, increases your risk greatly for adverse health consequences, including cardiovascular disease and early mortality,” Robbins said.
In a longitudinal study of 10,308 British civil servants published in 2007, researchers found that those who reduced their sleep from seven to five hours or fewer a night were almost twice as ly to die from all causes, especially cardiovascular disease.
Science has also linked poor slumber with high blood pressure, a weakened immune system, weight gain, a lack of libido, mood swings, paranoia, depression and a higher risk of diabetes, stroke, dementia and some cancers.
2. It’s healthy to be able to fall asleep ‘anywhere, anytime’
Falling asleep as soon as the car/train/airplane starts moving is not a sign of a well-rested person, sleep experts say. In fact, it’s just the opposite.
“Falling asleep instantly anywhere, anytime, is a sign that you are not getting enough sleep and you’re falling into ‘micro sleeps’ or mini-sleep episodes,” Robbins said. ‘It means your body is so exhausted that whenever it has a moment, it’s going to start to repay its sleep debt.”
You feel sleepy because of a buildup of a chemical called adenosine in the brain, which happens throughout the day as you head toward night. Sleeping soundly reduces that chemical so that when you wake up, the levels are at their lowest, and you feel refreshed.
But the longer you stay awake and the less sleep you get, the more your adenosine levels rise, creating what’s called a sleep load or sleep debt.
Want to check your level of sleepiness? Look at the Epworth sleepiness scale, and if you’re worried, check in with a sleep doctor who can do more extensive testing in a sleep lab.
3. Your brain and body can adapt to less sleep
People also believed that the brain and body could adapt and learn to function optimally with less sleep. That too is a myth, experts say. That’s because your body cycles through four distinct phases of sleep to fully restore itself.
In stage one, you start to lightly sleep, and you become disengaged from your environment in stage two, where you will spend most of your total sleep time. Stages three and four contain the deepest, most restorative sleep and the dreamy state of REM, or rapid eye movement sleep.
“During REM, the brain is highly reactive,” Robbins said. “It almost looks your brain is awake if we hook you up to two more electrodes and were able to monitor your brain waves.”
REM can occur any time during the sleep cycle, but on average, it starts about 90 minutes after you’ve fallen asleep. REM is when your body and brain are busy storing memories, regulating mood and learning. It’s also when you dream. Your arm and leg muscles are temporarily paralyzed during REM sleep, so you can’t act out your dreams and injure yourself.
Because a good night’s sleep gives your sleep cycle time to repeat, you’ll go through several REM cycles, which take up about 25% of your total sleeping time.
Another important stage of sleep is deep sleep, when your brain waves slow into what is called delta waves or slow-wave sleep. It’s the time when human growth hormone is released and memories are further processed.
“The deeper stages of sleep are really important for generation of neurons, repairing muscle and restoring the immune system,” Robbins said.
It’s tough to wake a person from deep sleep. If you do wake, you can feel groggy and fatigued; mental performance can be affected for up to 30 minutes, studies show.
4. Snoring, although annoying, is mostly harmless
In your dreams, maybe. In fact, “loud, raucous snores interrupted by pauses in breathing” is a marker for sleep apnea, a dangerous sleep disorder that, according to the National Heart, Lung and Blood Institute, increases risk for heart attacks, atrial fibrillation, asthma, high blood pressure, glaucoma, cancer, diabetes, kidney disease and cognitive and behavior disorders.
“Sleep apnea is extremely exhausting,” Robbins said. “These patients sleep and then they wake up over and over; then they are fighting sleep all day long because they’re so exhausted. It’s also very underdiagnosed. We believe it affects about 30% of the population, and around 10% are diagnosed.”
5. Drinking alcohol before bed helps you fall sleep
Do you think a nightcap before bed will help you fall asleep and stay asleep? Dream on.
Alcohol may help you fall asleep, but that’s where the benefits end, Robbins said. Instead, it traps you in the lighter stages of sleep and “dramatically reduces the quality of your rest at night.”
“It continues to pull you rapid eye movement and the deeper stages of sleep, causing you to wake up not feeling restored,” Robbins said.
6. Not sleeping? Stay in bed with eyes closed and try and try
You have to admit, it makes sense: How can you fall asleep if you’re not in the bed trying? Yet sleep experts say that continuing to count sheep for more than 15 minutes isn’t the smartest move.
“If we stay in bed, we’ll start to associate the bed with insomnia,” Robbins said. She equates it to “going to the gym and standing on a treadmill and not doing anything.”
In reality, Robbins said, it takes a healthy sleeper about 15 minutes to fall asleep. If you’re tossing and turning much longer than that, you should get bed, change the environment and do something mindless: “Keep the lights low and fold socks,” she suggested.
Some people also believe that it’s just as refreshing to your body to lie in bed with eyes closed but not sleeping. Nope. That’s another pipe dream, experts say.
7. It doesn’t matter what time of day you sleep
Sleep experts say that’s another myth that can negatively affect your health.
“We recommend that people have a regular sleep schedule because it controls what we call the biological clock, or circadian rhythm, of the body,” Jean-Louis said. “That controls all the hormones of the body, body temperature, eating and digestion, and sleep-wake cycles.”
When your inner clock and the outside world are phase, you can feel disoriented, mentally foggy and sleepy at times when you need to be functioning at optimal levels. Just think of what happens when you travel across time zones or when daylight savings time kicks in.
Studies of shift workers, who work unusual hours andlive sync with their normal biological rhythm, show that they are at increased risk for heart disease, ulcers, depression, obesity and certain cancers, as well as a higher rate of workplace accidents and injuries due to a slower reaction rate and poor decision-making.
8. Watching TV in bed helps you relax
Come on, we all do it — or we check our laptop or smartphone before we power down for the night. Unfortunately, that sets us up for a bad night.
“These devices emit bright blue light, and that blue light is what tells our brain to become alive and alert in the morning,” Robbins explained. “We want to avoid blue light before bed, from sources a television or your smartphone, and do things that relax you.”
According to the National Sleep Foundation, blue light affects the release of melatonin, the sleep hormone, more than any other wavelength of light. Watching TV or using an electronic device within two hours of bedtime means it will take you longer to fall asleep, you’ll have less dream state or REM sleep, and even if you do sleep eight or more hours, you’ll wake feeling groggy.
If you or your children can’t make that two-hour cutoff because of homework or late-night work demands, experts suggest dimming the brightness of the screen or installing an app that can warm the screen to the sunset colors. Red and yellow have higher wavelengths and don’t affect melatonin.
9. Hitting snooze is great! No need to get up right away
Raise your hand if you hit the snooze button. Why not, right?
“Resist the temptation to snooze, because unfortunately, your body will go back to sleep — a very light, low-quality sleep,” Robbins said.
As you near the end of your sleep, your body is probably nearing the end of its last REM cycle. Hit that snooze button, and the brain falls right back into a new REM cycle. Now, when the alarm goes off a few minutes later, you’ll be in the middle, not the end, of that cycle, and you’ll wake up groggy and stay that way longer.
Having trouble kicking the snooze button habit? Put the alarm on the other side of the room, so you have to get bed to turn it off.
And no, you can’t tell Google or Alexa to turn it off. That’s cheating.
10. Remembering your dreams is a sign of good sleep
“That’s a myth, because all of us do experience dreams four to five times a night,” Jean-Louis said. “And we don’t remember because we’ve not woken up and disrupted our sleep.”
A study France showed that people who frequently remember their dreams have higher brain activity in the information-processing hub of the brains. They also woke twice as often during the night and were more sensitive to sounds when sleeping and awake.
“Now, I will tell you if you have a dream with a strong emotional context, it may come back to you at say, two o’clock in the afternoon, when you have some downtime to relax,” Jean-Louis said. “Sometimes, something would trigger that. But if it is a weird little mundane dream, most of us who sleep well don’t remember those.”
The research team found more myths that we tend to accept as fact, Jean-Louis said, such as “more sleep is always better” (no, you really can sleep too much and harm your health), “taking a nap in the afternoon can fix insomnia” (actually, if you sleep long enough to enter a REM or deep sleep cycle, it can mess up your body clock even more), and “it’s better to have a warm than cool bedroom” (no, you sleep better in cooler temps).
Which means that we could all use a bit of education about good sleep hygiene, a set of habits to form that will set you up for a lifetime of healthy sleep. The National Sleep Foundation has tips, as does the CDC.
After all, there’s no amount of caffeine that can help you deal with the adverse implications of insufficient sleep, nor can you train yourself to adapt to sleep deprivation, Robbins said.
“Sleep is a highly active process,” she said. “It’s crucial, actually, in restoring the body and is in fact the most efficient, effective way to do so.”
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EEG tests and epilepsy
An EEG (electroencephalogram) may be done in hospital in an outpatient clinic by a highly trained specialist called a clinical neurophysiologist. Sometimes it may be done at home. You will be shown how to do this.
Your doctor might ask you to have an EEG test if:
- They think you might have epilepsy or
- You have epilepsy, and they need to know more about it or
- They are unsure whether or not your seizures are epilepsy or
- You are being considered for epilepsy surgery or
- They want to withdraw your epilepsy medicines
Sometimes an EEG is done to check whether someone is in non-convulsive status epilepticus. Non-convulsive status epilepticus can change a person’s level of awareness or cause confusion, but might not be recognised as a seizure without an EEG.
The results of an EEG can help doctors to make the right diagnosis and decide on the best treatment. They should always be interpreted by someone who specialises in reading EEG results. This is because reading an EEG incorrectly is one of the most common reasons for people to be given the wrong diagnosis.
What does an EEG test do?
Your brain constantly produces tiny electrical signals. During an EEG test, small sensors, called electrodes, are placed on your scalp. They are attached using a special glue or paste. These are connected by wires to an EEG recording machine. The electrodes pick up the electrical signals from your brain and record them on a computer.
The electrodes only pick up the electrical signals. They don’t affect your brain and they don’t cause you any pain.
The electrical signals look wavy lines and these wavy lines show your brainwave patterns. The EEG test can only show your brainwave patterns at the time the test is carried out. At different times, your brainwave patterns may be different.
Most people’s brainwave patterns look similar to other people’s. Sometimes the EEG test shows that a person has different brainwave patterns to other people. These are caused by unusual electrical activity in their brain. They can sometimes, but not always, show that the person has epilepsy.
What information does an EEG test give?
An EEG test gives information about the electrical activity that is happening in your brain at the time the test is carried out.
With many types of epilepsy, you only have unusual electrical activity in your brain when you are having a seizure. The rest of the time your brain activity is normal.
So, if your EEG test doesn’t show any unusual activity, it usually means that there is no epileptic activity in your brain at the time the test is being done.
This doesn’t prove that you don’t have epileptic activity in your brain at other times. And it doesn’t mean that you don’t have epilepsy.
People with some types of epilepsy have unusual electrical activity in their brain all the time, even when they are not having a seizure. When they have an EEG test, the results can show certain brainwave patterns that doctors recognise. This information is very helpful for doctors when they are making a diagnosis.
A small number of people have unusual EEG test results, even though they never have seizures and they don’t have epilepsy. These could be caused by other medical conditions, problems with their vision, or brain damage. So, an EEG that shows unusual brainwave patterns doesn’t always mean that you have epilepsy.
Can an EEG test show what type of seizures I have?
When an EEG test picks up unusual electrical activity, it shows the areas of your brain where it is coming from. And it can also show up some types of seizure. But it might not show up some focal (partial) seizures unless they involve a lack of awareness.
Can an EEG test show if there is any damage in my brain?
An EEG test only gives information about the electrical activity in your brain. It doesn’t show if there’s any damage or physical abnormalities in your brain.
Will an EEG test cause me to have a seizure?
There’s a very small risk that you could have a seizure during an EEG test. This could be caused by looking at a flashing light or breathing deeply. These activities are usually part of the test.
Your doctor might ask you to reduce your epilepsy medicine or have less sleep than usual before you have some types of EEG tests. This would also increase the risk that you would have a seizure around the time of having the test.
Will I have to give my consent (permission) for an EEG test to be done?
You will usually have to give your consent to having an EEG test done. This is because there is a risk of having a seizure during the test. A video recording is usually taken as part of the EEG test. Your consent will also be needed for this.
Depending on your hospital, you might be asked to give your consent:
- By your consultant when they refer you to have an EEG or
- By post, if you are sent a consent form with the appointment letter or
- At the hospital, just before the test is carried out
If you give your consent, but then change your mind, you can withdraw your consent at any time.
Will having a seizure during an EEG test affect my right to drive?
If you hold a driving licence, having a seizure could mean that you have to stop driving until you have been seizure free for 12 months.
If you are concerned about the risk of having a seizure, talk to the doctor who has asked you to have the test.
Will I have to have more than one EEG test?
There are several ways an EEG test can be done.
If you have an EEG test that doesn’t show any unusual electrical activity in your brain, your doctor might ask you to have another. It can be helpful, if possible, to have an EEG test at times when you are more ly to have a seizure. For example, this might be early in the morning. For some women, it might be around the time of having a period.
Standard EEG tests
You will usually have a standard EEG test at an outpatient’s appointment at the hospital. During the test, you sit or lie down. You may be asked to breathe deeply for some minutes and also to look at a flashing light. These activities can change the electrical activity in your brain, and this will show on the computer. This can help the doctor to make a diagnosis.
You will be asked to keep as still as possible during the test. Any movement can change the electrical activity in your brain, which can affect the results
Routine EEG recordings usually take 20 to 40 minutes, although a typical appointment will last about an hour, including some preparation time at the beginning and some time at the end. Other types of EEG recording may take longer. You can go home as soon as the test has been done.
Evelina Children’s Hospital has made a film about having an EEG. The film shows having an EEG at Evelina. Services at other hospitals may be different.
Sleep EEG tests
Your doctor might ask you to have an EEG test while you are asleep. This could be because your seizures happen when you are asleep.
Or you may have had a standard EEG test when you were awake, but it didn’t show any unusual electrical activity. When you are asleep, your brainwave patterns change and may show more unusual electrical activity.
There are also some types of seizure that mainly happen during sleep.
A sleep EEG test is usually done in hospital, using a standard EEG machine. Before the test, you may be given some medicine to make you go to sleep. The test lasts for one to two hours and you usually go home once you have woken up.
Sleep EEGs can be particularly useful when epilepsy is suspected in children under 5. This is because there are some types of epilepsy which are common in young children, where seizures mainly happen in sleep. Examples are the epilepsy syndromes autosomal dominant nocturnal frontal lobe epilepsy and electrical status epilepticus during slow wave sleep (ESESS).
For some older people, a sleep EEG can also be useful as brainwave patterns related to focal seizures are more ly to be seen in sleep. Focal seizures are the most common type of seizure in older people.
Sleep-deprived EEG tests
A sleep-deprived EEG test is done when you have had less sleep than usual. When you are tired, there is more chance that there will be unusual electrical activity in your brain.
Your doctor might ask you to have this test if you have had a standard EEG test, but it didn’t show any unusual electrical activity.
A sleep-deprived EEG can show up subtle seizures, including absence, myoclonic or focal (partial) seizures.
Before you have a sleep-deprived EEG test, your doctor may ask you not to go to sleep at all the night before. Or they may ask you to wake up much earlier than you usually do.
The beginning of the sleep-deprived EEG test is the same as a standard EEG test. You may then fall asleep or doze while the EEG is still recording the activity in your brain. The test lasts for a few hours and you usually go home once you have woken up.
Ambulatory EEG tests
Ambulatory means designed for walking. So you can have an ambulatory EEG test while you are moving around. An ambulatory EEG test is designed to record the activity in your brain over a few hours, days or weeks. This means there is more chance that it will pick up unusual electrical activity in your brain, than during a standard or sleep EEG test.
An ambulatory EEG uses electrodes similar to those used on a standard EEG test. However, the electrodes that are attached to your head are plugged in to a small machine that records the results. You can wear the machine on a belt, so you are able to go about your daily business. You don’t usually stay in hospital while the test is being done.
Your doctor will ask you to keep a diary of your activities, such as sleeping and eating, while you are wearing the ambulatory EEG. They will also ask you, or somebody who is with you, to keep a detailed record of any seizures you have. They will then be able to match up what has been happening with the results of your brainwave activity on the EEG test results.
During a video-telemetry test (vEEG), you need to stay in hospital. A vEEG involves wearing an ambulatory EEG. At the same time, all your movements are recorded by a video camera. The test is usually carried out over a few days. Sometimes your epilepsy medicine is reduced or withdrawn. This is to increase the chances that you will have a seizure that can be recorded.
After the test, doctors can watch the video to see any seizures that you had. They can also look at the EEG results for the time you were having the seizure. This will tell them about any changes to your brainwave patterns at the time of the seizures.
Home video-telemetry can be done at home in a similar way to an ambulatory EEG. You will be shown how to set up the equipment, which will include a video recorder.
You will usually have had other types of EEG tests before you are considered for a vEEG. Here are some examples of why your doctor might ask you to have a vEEG:
- It’s not clear what type of seizures you have or
- Your epilepsy medicine isn’t working well or
- There’s a possibility that your seizures are not caused by epilepsy, but something else or
- You’re being assessed for epilepsy surgery
Evelina Children’s Hospital has made a film about home video-telemetry. The film shows how the home video-telemetry service works at Evelina. Services at other hospitals may be different.
Some people who are being considered for surgery will have invasive EEG-telemetry (iEEG). A neurosurgeon will do an operation to place the EEG electrodes directly onto the surface of the brain or into the brain. The electrodes are called ‘strip’ or ‘grid’ or ‘stereo’ electrodes.
The reason for iEEG is to find out where exactly your seizures are coming from. Another part of this test is called ‘cortical mapping’. Cortical mapping is done to see exactly which part of your brain is responsible for things your memory or speech. It is done to reduce the risk of complications after surgery.
If you have any other questions before an EEG test, you could ask your family doctor, epilepsy specialist, epilepsy specialist nurse or the person who will carry out the test.
If you would to see this information with references, visit the Advice and Information references section of our website. If you are unable to access the internet, please contact our Epilepsy Action Helpline freephone on 0808 800 5050.