105-500: A sleeper is a person who is sleeping . Sleeper may also refer to: Sleep Sleep is a state of reduced mental and physical activity in which consciousness is altered and certain sensory activity is inhibited. During sleep, there is a marked decrease in muscle activity and interactions with the surrounding environment. While sleep differs from wakefulness in terms of the ability to react to stimuli , it still involves active brain patterns, making it more reactive than
210-407: A coma or disorders of consciousness . Sleep occurs in repeating periods , during which the body alternates between two distinct modes: REM and non-REM sleep . Although REM stands for "rapid eye movement", this mode of sleep has many other aspects, including virtual paralysis of the body. Dreams are a succession of images, ideas, emotions, and sensations that usually occur involuntarily in
315-509: A seizure is occurring. This is known as an ictal recording, as opposed to an interictal recording, which refers to the EEG recording between seizures. To obtain an ictal recording, a prolonged EEG is typically performed accompanied by a time-synchronized video and audio recording. This can be done either as an outpatient (at home) or during a hospital admission, preferably to an Epilepsy Monitoring Unit (EMU) with nurses and other personnel trained in
420-472: A voltmeter . Recording these voltages over time gives us the EEG. The electric potential generated by an individual neuron is far too small to be picked up by EEG or MEG. EEG activity therefore always reflects the summation of the synchronous activity of thousands or millions of neurons that have similar spatial orientation. If the cells do not have similar spatial orientation, their ions do not line up and create waves to be detected. Pyramidal neurons of
525-405: A 24-hour cycle, whereas in monophasic sleep this occurs all at once. Under experimental conditions, humans tend to alternate more frequently between sleep and wakefulness (i.e., exhibit more polyphasic sleep) if they have nothing better to do. Given a 14-hour period of darkness in experimental conditions, humans tended towards bimodal sleep, with two sleep periods concentrated at the beginning and at
630-407: A brain area directly above the optic chiasm , is presently considered the most important nexus for this process; however, secondary clock systems have been found throughout the body. An organism whose circadian clock exhibits a regular rhythm corresponding to outside signals is said to be entrained ; an entrained rhythm persists even if the outside signals suddenly disappear. If an entrained human
735-538: A child's quality of sleep as well as prepare them to make and keep healthy sleep hygiene habits in the future. Children need many hours of sleep per day in order to develop and function properly: up to 18 hours for newborn babies, with a declining rate as a child ages. Early in 2015, after a two-year study, the National Sleep Foundation in the US announced newly revised recommendations as shown in
840-705: A combined EEG/MEG (EMEG) approach has been investigated for the purpose of source reconstruction in epilepsy diagnosis. EEG has also been combined with positron emission tomography . This provides the advantage of allowing researchers to see what EEG signals are associated with different drug actions in the brain. Recent studies using machine learning techniques such as neural networks with statistical temporal features extracted from frontal lobe EEG brainwave data has shown high levels of success in classifying mental states (Relaxed, Neutral, Concentrating), mental emotional states (Negative, Neutral, Positive) and thalamocortical dysrhythmia . The brain's electrical charge
945-414: A factor which may exacerbate disruption of the circadian cycle. Scientific studies on sleep have shown that sleep stage at awakening is an important factor in amplifying sleep inertia . Determinants of alertness after waking up include quantity/quality of the sleep, physical activity the day prior, a carbohydrate-rich breakfast, and a low blood glucose response to it. Sleep timing is controlled by
1050-616: A full eight hours. Researchers have found that sleeping 6–7 hours each night correlates with longevity and cardiac health in humans, though many underlying factors may be involved in the causality behind this relationship. Sleep difficulties are furthermore associated with psychiatric disorders such as depression , alcoholism , and bipolar disorder . Up to 90 percent of adults with depression are found to have sleep difficulties. Dysregulation detected by EEG includes disturbances in sleep continuity, decreased delta sleep and altered REM patterns with regard to latency, distribution across
1155-407: A function of the amount of time elapsed since the last adequate sleep episode) must be balanced against the circadian element for satisfactory sleep. Along with corresponding messages from the circadian clock, this tells the body it needs to sleep. The timing is correct when the following two circadian markers occur after the middle of the sleep episode and before awakening: maximum concentration of
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#17327810482711260-413: A good night's sleep. The American Academy of Sleep Medicine (AASM) divides NREM into three stages: N1, N2, and N3, the last of which is also called delta sleep or slow-wave sleep . The whole period normally proceeds in the order: N1 → N2 → N3 → N2 → REM. REM sleep occurs as a person returns to stage 2 or 1 from a deep sleep. There is a greater amount of deep sleep (stage N3) earlier in the night, while
1365-444: A longer duration in the epilepsy monitoring unit (EMU) or at home with an ambulatory EEG. In addition, there are activating maneuvers such as photic stimulation, hyperventilation and sleep deprivation that can increase the diagnostic yield of the EEG. At times, a routine EEG is not sufficient to establish the diagnosis or determine the best course of action in terms of treatment. In this case, attempts may be made to record an EEG while
1470-418: A particular frequency corresponds to various points in the sleep-wake cycle, such as being asleep, being awake, or falling asleep. Alpha, beta, theta, gamma, and delta waves are all seen in the different stages of sleep. Each waveform maintains a different frequency and amplitude. Alpha waves are seen when a person is in a resting state, but is still fully conscious. Their eyes may be closed and all of their body
1575-541: A person is. The range of frequencies one observes are between 1 and 30 Hz, and amplitudes will vary between 20 and 100 μV. The observed frequencies are subdivided into various groups: alpha (8–13 Hz), beta (13–30 Hz), delta (0.5–4 Hz), and theta (4–7 Hz). Alpha waves are observed when a person is in a state of relaxed wakefulness and are mostly prominent over the parietal and occipital sites. During intense mental activity , beta waves are more prominent in frontal areas as well as other regions. If
1680-456: A relaxed person is told to open their eyes, one observes alpha activity decreasing and an increase in beta activity. Theta and delta waves are not generally seen in wakefulness - if they are, it is a sign of brain dysfunction. EEG can detect abnormal electrical discharges such as sharp waves , spikes, or spike-and-wave complexes, as observable in people with epilepsy ; thus, it is often used to inform medical diagnosis . EEG can detect
1785-506: A research method). In cases where significant brain injury is suspected, e.g., after cardiac arrest, EEG can provide some prognostic information. If a patient with epilepsy is being considered for resective surgery to treat epilepsy, it is often necessary to localize the focus (source) of the epileptic brain activity with a resolution greater than what is provided by scalp EEG. In these cases, neurosurgeons typically implant strips and grids of electrodes or penetrating depth electrodes under
1890-445: A screen before bed may interfere with sleep. Modern humans often find themselves desynchronized from their internal circadian clock, due to the requirements of work (especially night shifts ), long-distance travel, and the influence of universal indoor lighting. Even if they have sleep debt, or feel sleepy, people can have difficulty staying asleep at the peak of their circadian cycle. Conversely, they can have difficulty waking up in
1995-410: A smaller parcel of brain surface) allow for better spatial resolution to narrow down the areas critical for seizure onset and propagation. Some clinical sites record data from penetrating microelectrodes. Sometimes it is more convenient or clinically necessary to perform ambulatory EEG recordings in the home of the person being tested. These studies typically have a duration of 24–72 hours. EEG and
2100-428: A span of hours. Therefore, research has been directed to developing dry and semi-dry EEG bioelectronic interfaces. Dry electrode signals depend upon mechanical contact. Therefore, it can be difficult getting a usable signal because of impedance between the skin and the electrode. Some EEG systems attempt to circumvent this issue by applying a saline solution. Others have a semi dry nature and release small amounts of
2205-438: A structured bedtime routine. This can look differently among families, but will generally consist of a set of rituals such as reading a bedtime story, a bath, brushing teeth, and can also include a show of affection from the parent to the child such a hug or kiss before bed. A bedtime routine will also include a consistent time that the child is expected to be in bed ready for sleep. Having a reliable bedtime routine can help improve
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#17327810482712310-611: A subjective point of view. Objective sleep quality refers to how difficult it is for a person to fall asleep and remain in a sleeping state, and how many times they wake up during a single night. Poor sleep quality disrupts the cycle of transition between the different stages of sleep. Subjective sleep quality in turn refers to a sense of being rested and regenerated after awaking from sleep. A study by A. Harvey et al. (2002) found that insomniacs were more demanding in their evaluations of sleep quality than individuals who had no sleep problems. Homeostatic sleep propensity (the need for sleep as
2415-540: A transitional period is called slow-wave sleep or deep sleep. During this phase, body temperature and heart rate fall, and the brain uses less energy. REM sleep, also known as paradoxical sleep, represents a smaller portion of total sleep time. It is the main occasion for dreams (or nightmares ), and is associated with desynchronized and fast brain waves, eye movements, loss of muscle tone, and suspension of homeostasis . The sleep cycle of alternate NREM and REM sleep takes an average of 90 minutes, occurring 4–6 times in
2520-522: Is adenosine , a neurotransmitter that inhibits many of the bodily processes associated with wakefulness. Adenosine levels increase in the cortex and basal forebrain during prolonged wakefulness, and decrease during the sleep-recovery period, potentially acting as a homeostatic regulator of sleep. Coffee , tea, and other sources of caffeine temporarily block the effect of adenosine, prolong sleep latency, and reduce total sleep time and quality. Humans are also influenced by aspects of social time , such as
2625-546: Is a method to record an electrogram of the spontaneous electrical activity of the brain . The biosignals detected by EEG have been shown to represent the postsynaptic potentials of pyramidal neurons in the neocortex and allocortex . It is typically non-invasive, with the EEG electrodes placed along the scalp (commonly called "scalp EEG") using the International 10–20 system , or variations of it. Electrocorticography , involving surgical placement of electrodes,
2730-447: Is a reliable indication of the occurrence of neural output. Not only do EEGs capture dendritic currents almost exclusively as opposed to axonal currents, they also show a preference for activity on populations of parallel dendrites and transmitting current in the same direction at the same time. Pyramidal neurons of cortical layers II/III and V extend apical dendrites to layer I. Currents moving up or down these processes underlie most of
2835-413: Is about 10 μV to 100 μV in amplitude when measured from the scalp. Since an EEG voltage signal represents a difference between the voltages at two electrodes, the display of the EEG for the reading encephalographer may be set up in one of several ways. The representation of the EEG channels is referred to as a montage. When analog (paper) EEGs are used, the technologist switches between montages during
2940-557: Is accumulated against an individual's average sleep or some other benchmark. It is also unclear whether the prevalence of sleep debt among adults has changed appreciably in the industrialized world in recent decades. Sleep debt does show some evidence of being cumulative. Subjectively, however, humans seem to reach maximum sleepiness 30 hours after waking. It is likely that in Western societies , children are sleeping less than they previously have. One neurochemical indicator of sleep debt
3045-525: Is an integrated system made of an array of capacitive sensors with local integrated circuitry housed in a package with batteries to power the circuitry. This level of integration was required to achieve the functional performance obtained by the electrode. The electrode was tested on an electrical test bench and on human subjects in four modalities of EEG activity, namely: (1) spontaneous EEG, (2) sensory event-related potentials, (3) brain stem potentials, and (4) cognitive event-related potentials. The performance of
3150-401: Is attached to an individual wire. Some systems use caps or nets into which electrodes are embedded; this is particularly common when high-density arrays of electrodes are needed. Electrode locations and names are specified by the International 10–20 system for most clinical and research applications (except when high-density arrays are used). This system ensures that the naming of electrodes
3255-413: Is confirmatory of epilepsy in nearly all cases (high specificity ), however up to 3.5% of the general population may have epileptiform abnormalities in an EEG without ever having had a seizure (low false positive rate ) or with a very low risk of developing epilepsy in the future. When a routine EEG is normal and there is a high suspicion or need to confirm epilepsy, it may be repeated or performed with
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3360-506: Is consistent across laboratories. In most clinical applications, 19 recording electrodes (plus ground and system reference) are used. A smaller number of electrodes are typically used when recording EEG from neonates . Additional electrodes can be added to the standard set-up when a clinical or research application demands increased spatial resolution for a particular area of the brain. High-density arrays (typically via cap or net) can contain up to 256 electrodes more-or-less evenly spaced around
3465-653: Is dark. The diverse purposes and mechanisms of sleep are the subject of substantial ongoing research. Sleep is a highly conserved behavior across animal evolution, likely going back hundreds of millions of years. Humans may suffer from various sleep disorders , including dyssomnias , such as insomnia , hypersomnia , narcolepsy , and sleep apnea ; parasomnias , such as sleepwalking and rapid eye movement sleep behavior disorder ; bruxism ; and circadian rhythm sleep disorders . The use of artificial light has substantially altered humanity's sleep patterns. Common sources of artificial light include outdoor lighting and
3570-399: Is isolated in a bunker with constant light or darkness, he or she will continue to experience rhythmic increases and decreases of body temperature and melatonin, on a period that slightly exceeds 24 hours. Scientists refer to such conditions as free-running of the circadian rhythm. Under natural conditions, light signals regularly adjust this period downward, so that it corresponds better with
3675-450: Is known as a "natural short sleeper". This condition is not to be confused with intentional sleep deprivation, which leaves symptoms such as irritability or temporarily impaired cognitive abilities in people who are predisposed to sleep a normal amount of time but not in people with FNSS. The genes DEC2 , ADRB1 , NPSR1 and GRM1 are implicated in enabling short sleep. The quality of sleep may be evaluated from an objective and
3780-410: Is maintained by billions of neurons . Neurons are electrically charged (or "polarized") by membrane transport proteins that pump ions across their membranes. Neurons are constantly exchanging ions with the extracellular milieu, for example to maintain resting potential and to propagate action potentials . Ions of similar charge repel each other, and when many ions are pushed out of many neurons at
3885-422: Is observed to be a necessary behavior across most of the animal kingdom, including some of the least cognitively advanced animals which have no need for other functions of sleep, such as memory consolidation or dreaming. It has been widely accepted that sleep must support the formation of long-term memory, and generally increasing previous learning and experiences recalls. However, its benefit seems to depend on
3990-452: Is processed in the same manner as digital scalp EEG (above), with a couple of caveats. ECoG is typically recorded at higher sampling rates than scalp EEG because of the requirements of Nyquist theorem – the subdural signal is composed of a higher predominance of higher frequency components. Also, many of the artifacts that affect scalp EEG do not impact ECoG, and therefore display filtering is often not needed. A typical adult human EEG signal
4095-443: Is profoundly influenced by changes in light, since these are its main clues about what time it is. Exposure to even small amounts of light during the night can suppress melatonin secretion, and increase body temperature and wakefulness. Short pulses of light, at the right moment in the circadian cycle, can significantly 'reset' the internal clock. Blue light, in particular, exerts the strongest effect, leading to concerns that use of
4200-400: Is regulated by a process called homeostasis . Induced or perceived lack of sleep is called sleep deprivation . Process S is driven by the depletion of glycogen and accumulation of adenosine in the forebrain that disinhibits the ventrolateral preoptic nucleus , allowing for inhibition of the ascending reticular activating system . Sleep deprivation tends to cause slower brain waves in
4305-443: Is resting and relatively still, where the body is starting to slow down. Beta waves take over alpha waves when a person is at attention, as they might be completing a task or concentrating on something. Beta waves consist of the highest of frequencies and the lowest of amplitude, and occur when a person is fully alert. Gamma waves are seen when a person is highly focused on a task or using all their concentration. Theta waves occur during
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4410-402: Is sometimes called "intracranial EEG" . Clinical interpretation of EEG recordings is most often performed by visual inspection of the tracing or quantitative EEG analysis . Voltage fluctuations measured by the EEG bioamplifier and electrodes allow the evaluation of normal brain activity . As the electrical activity monitored by EEG originates in neurons in the underlying brain tissue ,
4515-423: Is stored electronically and can be filtered for display. Typical settings for the high-pass filter and a low-pass filter are 0.5–1 Hz and 35–70 Hz respectively. The high-pass filter typically filters out slow artifact, such as electrogalvanic signals and movement artifact, whereas the low-pass filter filters out high-frequency artifacts, such as electromyographic signals. An additional notch filter
4620-465: Is the gold standard diagnostic procedure to confirm epilepsy . The sensitivity of a routine EEG to detect interictal epileptiform discharges at epilepsy centers has been reported to be in the range of 29–55%. Given the low to moderate sensitivity, a routine EEG (typically with a duration of 20–30 minutes) can be normal in people that have epilepsy. When an EEG shows interictal epileptiform discharges (e.g. sharp waves, spikes, spike-and-wave , etc.) it
4725-469: Is then filtered (next paragraph), and the EEG signal is output as the deflection of pens as paper passes underneath. Most EEG systems these days, however, are digital, and the amplified signal is digitized via an analog-to-digital converter , after being passed through an anti-aliasing filter . Analog-to-digital sampling typically occurs at 256–512 Hz in clinical scalp EEG; sampling rates of up to 20 kHz are used in some research applications. During
4830-600: Is typically used to remove artifact caused by electrical power lines (60 Hz in the United States and 50 Hz in many other countries). The EEG signals can be captured with opensource hardware such as OpenBCI and the signal can be processed by freely available EEG software such as EEGLAB or the Neurophysiological Biomarker Toolbox . As part of an evaluation for epilepsy surgery, it may be necessary to insert electrodes near
4935-488: The circadian clock (Process C), sleep-wake homeostasis (Process S), and to some extent by the individual will. Sleep timing depends greatly on hormonal signals from the circadian clock, or Process C, a complex neurochemical system which uses signals from an organism's environment to recreate an internal day–night rhythm. Process C counteracts the homeostatic drive for sleep during the day (in diurnal animals) and augments it at night. The suprachiasmatic nucleus (SCN),
5040-548: The dura mater , through either a craniotomy or a burr hole . The recording of these signals is referred to as electrocorticography (ECoG), subdural EEG (sdEEG), intracranial EEG (icEEG), or stereotactic EEG (sEEG). The signal recorded from ECoG is on a different scale of activity than the brain activity recorded from scalp EEG. Low-voltage, high-frequency components that cannot be seen easily (or at all) in scalp EEG can be seen clearly in ECoG. Further, smaller electrodes (which cover
5145-437: The frontal cortex , shortened attention span, higher anxiety, impaired memory, and a grouchy mood. Conversely, a well-rested organism tends to have improved memory and mood. Neurophysiological and functional imaging studies have demonstrated that frontal regions of the brain are particularly responsive to homeostatic sleep pressure. There is disagreement on how much sleep debt is possible to accumulate, and whether sleep debt
5250-432: The mind during certain stages of sleep. During sleep, most of the body's systems are in an anabolic state, helping to restore the immune , nervous , skeletal , and muscular systems; these are vital processes that maintain mood , memory , and cognitive function , and play a large role in the function of the endocrine and immune systems . The internal circadian clock promotes sleep daily at night , when it
5355-431: The EEG technique include evoked potentials (EP), which involves averaging the EEG activity time-locked to the presentation of a stimulus of some sort (visual, somatosensory , or auditory). Event-related potentials ( ERPs ) refer to averaged EEG responses that are time-locked to more complex processing of stimuli; this technique is used in cognitive science , cognitive psychology , and psychophysiological research. EEG
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#17327810482715460-402: The activity of cortical neurons near the electrodes on the scalp. Deep structures within the brain further away from the electrodes will not contribute directly to an EEG; these include the base of the cortical gyrus , mesial walls of the major lobes , hippocampus , thalamus , and brain stem . A healthy human EEG will show certain patterns of activity that correlate with how awake
5565-400: The advent of high-resolution anatomical imaging techniques such as magnetic resonance imaging (MRI) and computed tomography (CT). Despite its limited spatial resolution, EEG continues to be a valuable tool for research and diagnosis. It is one of the few mobile techniques available and offers millisecond-range temporal resolution, which is not possible with CT, PET, or MRI. Derivatives of
5670-582: The brain after concussion, however, at this time there are no advanced imaging techniques that can be used clinically to diagnose or monitor recovery from concussion. Several other methods to study brain function exist, including functional magnetic resonance imaging (fMRI), positron emission tomography (PET), magnetoencephalography (MEG), nuclear magnetic resonance spectroscopy (NMR or MRS), electrocorticography (ECoG), single-photon emission computed tomography (SPECT), near-infrared spectroscopy (NIRS), and event-related optical signal (EROS). Despite
5775-415: The brain and body, the reduced rate of metabolism enables countervailing restorative processes. The brain requires sleep for restoration, whereas these processes can take place during quiescent waking in the rest of the body. The essential function of sleep may be its restorative effect on the brain: "Sleep is of the brain, by the brain and for the brain." This theory is strengthened by the fact that sleep
5880-560: The brain restores its supply of adenosine triphosphate (ATP), the molecule used for short-term storage and transport of energy. In quiet waking, the brain is responsible for 20% of the body's energy use, thus this reduction has a noticeable effect on overall energy consumption. Sleep increases the sensory threshold . In other words, sleeping persons perceive fewer stimuli, but can generally still respond to loud noises and other salient sensory events. During slow-wave sleep , humans secrete bursts of growth hormone . All sleep, even during
5985-418: The care of patients with seizures. Outpatient ambulatory video EEGs typically last one to three days. An admission to an Epilepsy Monitoring Unit typically lasts several days but may last for a week or longer. While in the hospital, seizure medications are usually withdrawn to increase the odds that a seizure will occur during admission. For reasons of safety, medications are not withdrawn during an EEG outside of
6090-501: The cortex are thought to produce the most EEG signal because they are well-aligned and fire together. Because voltage field gradients fall off with the square of distance, activity from deep sources is more difficult to detect than currents near the skull. Scalp EEG activity shows oscillations at a variety of frequencies. Several of these oscillations have characteristic frequency ranges , spatial distributions and are associated with different states of brain functioning (e.g., waking and
6195-416: The cortex, inside sulci , in midline or deep structures (such as the cingulate gyrus or hippocampus ), or producing currents that are tangential to the skull, make far less contribution to the EEG signal. EEG recordings do not directly capture axonal action potentials . An action potential can be accurately represented as a current quadrupole , meaning that the resulting field decreases more rapidly than
6300-654: The day, is associated with the secretion of prolactin . Key physiological methods for monitoring and measuring changes during sleep include electroencephalography (EEG) of brain waves , electrooculography (EOG) of eye movements, and electromyography (EMG) of skeletal muscle activity. Simultaneous collection of these measurements is called polysomnography , and can be performed in a specialized sleep laboratory . Sleep researchers also use simplified electrocardiography (EKG) for cardiac activity and actigraphy for motor movements. The electrical activity seen on an EEG represents brain waves. The amplitude of EEG waves at
6405-926: The deepest period of sleep. Napping too long and entering the slow wave cycles can make it difficult to awake from the nap and leave one feeling unrested. This period of drowsiness is called sleep inertia . The siesta habit has recently been associated with a 37% lower coronary mortality, possibly due to reduced cardiovascular stress mediated by daytime sleep. Short naps at mid-day and mild evening exercise were found to be effective for improved sleep, cognitive tasks, and mental health in elderly people. Monozygotic (identical) but not dizygotic (fraternal) twins tend to have similar sleep habits. Neurotransmitters, molecules whose production can be traced to specific genes, are one genetic influence on sleep that can be analyzed. The circadian clock has its own set of genes. Genes which may influence sleep include ABCC9 , DEC2 , Dopamine receptor D2 and variants near PAX 8 and VRK2 . While
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#17327810482716510-526: The dry electrode compared favorably with that of the standard wet electrodes in terms of skin preparation, no gel requirements (dry), and higher signal-to-noise ratio. In 1999 researchers at Case Western Reserve University , in Cleveland , Ohio , led by Hunter Peckham, used 64-electrode EEG skullcap to return limited hand movements to quadriplegic Jim Jatich. As Jatich concentrated on simple but opposite concepts like up and down, his beta-rhythm EEG output
6615-514: The end of the dark time. Bimodal sleep in humans was more common before the Industrial Revolution . Different characteristic sleep patterns, such as the familiarly so-called " early bird " and " night owl ", are called chronotypes . Genetics and sex have some influence on chronotype, but so do habits. Chronotype is also liable to change over the course of a person's lifetime. Seven-year-olds are better disposed to wake up early in
6720-558: The end of the sleep cycle. Awakening involves heightened electrical activation in the brain, beginning with the thalamus and spreading throughout the cortex . On a typical night of sleep, there is not much time that is spent in the waking state. In various sleep studies that have been conducted using the electroencephalography, it has been found that females are awake for 0-1% during their nightly sleep while males are awake for 0-2% during that time. In adults, wakefulness increases, especially in later cycles. One study found 3% awake time in
6825-486: The exact 24 hours of an Earth day. The circadian clock exerts constant influence on the body, affecting sinusoidal oscillation of body temperature between roughly 36.2 °C and 37.2 °C. The suprachiasmatic nucleus itself shows conspicuous oscillation activity, which intensifies during subjective day (i.e., the part of the rhythm corresponding with daytime, whether accurately or not) and drops to almost nothing during subjective night. The circadian pacemaker in
6930-533: The first ninety-minute sleep cycle, 8% in the second, 10% in the third, 12% in the fourth, and 13–14% in the fifth. Most of this awake time occurred shortly after REM sleep. Today, many humans wake up with an alarm clock ; however, people can also reliably wake themselves up at a specific time with no need for an alarm. Many sleep quite differently on workdays versus days off, a pattern which can lead to chronic circadian desynchronization. Many people regularly look at television and other screens before going to bed,
7035-608: The first single and also multichannel dry active electrode arrays using micro-machining. The single channel dry EEG electrode construction and results were published in 1994. The arrayed electrode was also demonstrated to perform well compared to silver / silver chloride electrodes. The device consisted of four sites of sensors with integrated electronics to reduce noise by impedance matching . The advantages of such electrodes are: (1) no electrolyte used, (2) no skin preparation, (3) significantly reduced sensor size, and (4) compatibility with EEG monitoring systems. The active electrode array
7140-454: The following disorders: It can also: EEG can also be used in intensive care units for brain function monitoring to monitor for non-convulsive seizures/non-convulsive status epilepticus, to monitor the effect of sedative/anesthesia in patients in medically induced coma (for treatment of refractory seizures or increased intracranial pressure ), and to monitor for secondary brain damage in conditions such as subarachnoid hemorrhage (currently
7245-414: The gel upon contact with the scalp. Another solution uses spring loaded pin setups. These may be uncomfortable. They may also be dangerous if they were used in a situation where a patient could bump their head since they could become lodged after an impact trauma incident. Currently, headsets are available incorporating dry electrodes with up to 30 channels. Such designs are able to compensate for some of
7350-412: The highest rate of sleep. The hours that children spend asleep influence their ability to perform on cognitive tasks. Children who sleep through the night and have few night waking episodes have higher cognitive attainments and easier temperaments than other children. Sleep also influences language development. To test this, researchers taught infants a faux language and observed their recollection of
7455-448: The hormone melatonin, and minimum core body temperature. Human sleep-needs vary by age and amongst individuals; sleep is considered to be adequate when there is no daytime sleepiness or dysfunction. Moreover, self-reported sleep duration is only moderately correlated with actual sleep time as measured by actigraphy , and those affected with sleep state misperception may typically report having slept only four hours despite having slept
7560-675: The hospital. Ambulatory video EEGs, therefore, have the advantage of convenience and are less expensive than a hospital admission, but they also have the disadvantage of a decreased probability of recording a clinical event. Epilepsy monitoring is often considered when patients continue having events despite being on anti-seizure medications or if there is concern that the patient's events have an alternate diagnosis, e.g., psychogenic non-epileptic seizures , syncope (fainting) , sub-cortical movement disorders , migraine variants, stroke, etc. In cases of epileptic seizures, continuous EEG monitoring helps to characterize seizures and localize/lateralize
7665-475: The hours when other people are awake, the hours when work is required, the time on clocks, etc. Time zones , standard times used to unify the timing for people in the same area, correspond only approximately to the natural rising and setting of the sun. An extreme example of the approximate nature of time zones is China, a country which used to span five time zones and now officially uses only one (UTC+8). In polyphasic sleep , an organism sleeps several times in
7770-409: The interpretation of EEGs for clinical purposes. This is done by visual inspection of the waveforms, called graphoelements. The use of computer signal processing of the EEG – so-called quantitative electroencephalography – is somewhat controversial when used for clinical purposes (although there are many research uses). In the early 1990s Babak Taheri, at University of California, Davis demonstrated
7875-489: The latter have been found in a GWAS study that primarily detects correlations (but not necessarily causation), other genes have been shown to have a more direct effect. For instance, mice lacking dihydropyrimidine dehydrogenase (Dpyd) had 78.4 min less sleep during the lights-off period than wild-type mice. Dpyd encodes the rate-limiting enzyme in the metabolic pathway that catabolizes uracil and thymidine to β- alanine , an inhibitory neurotransmitter . This also supports
7980-422: The middle of the night. Circadian rhythm exerts some influence on the nighttime secretion of growth hormone. The circadian rhythm influences the ideal timing of a restorative sleep episode. Sleepiness increases during the night. REM sleep occurs more during body temperature minimum within the circadian cycle, whereas slow-wave sleep can occur more independently of circadian time. The internal circadian clock
8085-496: The morning than are fifteen-year-olds. Chronotypes far outside the normal range are called circadian rhythm sleep disorders. Naps are short periods of sleep that one might take during the daytime, often in order to get the necessary amount of rest. Napping is often associated with childhood, but around one-third of American adults partake in it daily. The optimal nap duration is around 10–20 minutes, as researchers have proven that it takes at least 30 minutes to enter slow-wave sleep,
8190-405: The night and density of eye movements. Sleep duration can also vary according to season. Up to 90% of people report longer sleep duration in winter, which may lead to more pronounced seasonal affective disorder . By the time infants reach the age of two, their brain size has reached 90 percent of an adult-sized brain; a majority of this brain growth has occurred during the period of life with
8295-473: The ones produced by the current dipole of post-synaptic potentials. In addition, since EEGs represent averages of thousands of neurons, a large population of cells in synchronous activity is necessary to cause a significant deflection on the recordings. Action potentials are very fast and, as a consequence, the chances of field summation are slim. However, neural backpropagation , as a typically longer dendritic current dipole, can be picked up by EEG electrodes and
8400-419: The onset and spatio-temporal (location and time) evolution of seizures and the presence of status epilepticus . It is also used to help diagnose sleep disorders , depth of anesthesia , coma , encephalopathies , cerebral hypoxia after cardiac arrest , and brain death . EEG used to be a first-line method of diagnosis for tumors , stroke , and other focal brain disorders, but this use has decreased with
8505-466: The period of a person being awake, and they continue to transition into Stage 1 of sleep and in stage 2. Delta waves are seen in stages 3 and 4 of sleep when a person is in their deepest of sleep. Sleep is divided into two broad types: non-rapid eye movement (non-REM or NREM) sleep and rapid eye movement (REM) sleep. Non-REM and REM sleep are so different that physiologists identify them as distinct behavioral states. Non-REM sleep occurs first and after
8610-434: The phase of sleep and the type of memory. For example, declarative and procedural memory-recall tasks applied over early and late nocturnal sleep, as well as wakefulness controlled conditions, have been shown that declarative memory improves more during early sleep (dominated by SWS) while procedural memory during late sleep (dominated by REM sleep) does so. Electroencephalography Electroencephalography ( EEG )
8715-451: The proportion of REM sleep increases in the two cycles just before natural awakening. Awakening can mean the end of sleep, or simply a moment to survey the environment and readjust body position before falling back asleep. Sleepers typically awaken soon after the end of a REM phase or sometimes in the middle of REM. Internal circadian indicators , along with a successful reduction of homeostatic sleep need, typically bring about awakening and
8820-542: The recording in order to highlight or better characterize certain features of the EEG. With digital EEG, all signals are typically digitized and stored in a particular (usually referential) montage; since any montage can be constructed mathematically from any other, the EEG can be viewed by the electroencephalographer in any display montage that is desired. The EEG is read by a clinical neurophysiologist or neurologist (depending on local custom and law regarding medical specialities ), optimally one who has specific training in
8925-422: The recording, a series of activation procedures may be used. These procedures may induce normal or abnormal EEG activity that might not otherwise be seen. These procedures include hyperventilation, photic stimulation (with a strobe light), eye closure, mental activity, sleep and sleep deprivation. During (inpatient) epilepsy monitoring, a patient's typical seizure medications may be withdrawn. The digital EEG signal
9030-429: The recordings made by the electrodes on the surface of the scalp vary in accordance with their orientation and distance to the source of the activity. Furthermore, the value recorded is distorted by intermediary tissues and bones, which act in a manner akin to resistors and capacitors in an electrical circuit . This means that not all neurons will contribute equally to an EEG signal, with an EEG predominately reflecting
9135-677: The region of the brain from which a seizure originates. This can help identify appropriate non-medication treatment options. In clinical use, EEG traces are visually analyzed by neurologists to look at various features. Increasingly, quantitative analysis of EEG is being used in conjunction with visual analysis. Quantitative analysis displays like power spectrum analysis, alpha-delta ratio, amplitude integrated EEG, and spike detection can help quickly identify segments of EEG that need close visual analysis or, in some cases, be used as surrogates for quick identification of seizures in long-term recordings. An EEG might also be helpful for diagnosing or treating
9240-434: The related study of ERPs are used extensively in neuroscience , cognitive science , cognitive psychology , neurolinguistics , and psychophysiological research, as well as to study human functions such as swallowing. Any EEG techniques used in research are not sufficiently standardised for clinical use, and many ERP studies fail to report all of the necessary processing steps for data collection and reduction, limiting
9345-500: The relatively poor spatial sensitivity of EEG, the "one-dimensional signals from localised peripheral regions on the head make it attractive for its simplistic fidelity and has allowed high clinical and basic research throughput". Thus, EEG possesses some advantages over some of those other techniques: EEG also has some characteristics that compare favorably with behavioral testing: Simultaneous EEG recordings and fMRI scans have been obtained successfully, though recording both at
9450-607: The reproducibility and replicability of many studies. Based on a 2024 systematic literature review and meta analysis commissioned by the Patient-Centered Outcomes Research Institute (PCORI), EEG scans cannot be used reliably to assist in making a clinical diagnosis of ADHD. However, EEG continues to be used in research on mental disabilities, such as auditory processing disorder (APD), ADD , and ADHD . EEGs have also been studied for their utility in detecting neurophysiological changes in
9555-435: The role of β-alanine as a neurotransmitter that promotes sleep in mice. Familial natural short sleep is a rare, genetic, typically inherited trait where an individual sleeps for fewer hours than average without suffering from daytime sleepiness or other consequences of sleep deprivation . This process is entirely natural in this kind of individual, and it is caused by certain genetic mutations. A person with this trait
9660-400: The rules for that language. Infants who slept within four hours of learning the language could remember the language rules better, while infants who stayed awake longer did not recall those rules as well. There is also a relationship between infants' vocabulary and sleeping: infants who sleep longer at night at 12 months have better vocabularies at 26 months. Children can greatly benefit from
9765-911: The same time effectively requires that several technical difficulties be overcome, such as the presence of ballistocardiographic artifact, MRI pulse artifact and the induction of electrical currents in EEG wires that move within the strong magnetic fields of the MRI. While challenging, these have been successfully overcome in a number of studies. MRI's produce detailed images created by generating strong magnetic fields that may induce potentially harmful displacement force and torque. These fields produce potentially harmful radio frequency heating and create image artifacts rendering images useless. Due to these potential risks, only certain medical devices can be used in an MR environment. Similarly, simultaneous recordings with MEG and EEG have also been conducted, which has several advantages over using either technique alone: Recently,
9870-408: The same time, they can push their neighbours, who push their neighbours, and so on, in a wave. This process is known as volume conduction. When the wave of ions reaches the electrodes on the scalp, they can push or pull electrons on the metal in the electrodes. Since metal conducts the push and pull of electrons easily, the difference in push or pull voltages between any two electrodes can be measured by
9975-401: The scalp. Each electrode is connected to one input of a differential amplifier (one amplifier per pair of electrodes); a common system reference electrode is connected to the other input of each differential amplifier. These amplifiers amplify the voltage between the active electrode and the reference (typically 1,000–100,000 times, or 60–100 dB of power gain). In analog EEG, the signal
10080-471: The screens of electronic devices such as smartphones and televisions, which emit large amounts of blue light, a form of light typically associated with daytime. This disrupts the release of the hormone melatonin needed to regulate the sleep cycle . The most pronounced physiological changes in sleep occur in the brain. The brain uses significantly less energy during sleep than it does when awake, especially during non-REM sleep. In areas with reduced activity,
10185-437: The signal quality degradation related to high impedances by optimizing pre-amplification, shielding and supporting mechanics. EEG has several limitations. Most important is its poor spatial resolution. EEG is most sensitive to a particular set of post-synaptic potentials: those generated in superficial layers of the cortex, on the crests of gyri directly abutting the skull and radial to the skull. Dendrites which are deeper in
10290-400: The suprachiasmatic nucleus has a direct neural connection to the pineal gland , which releases the hormone melatonin at night. Cortisol levels typically rise throughout the night, peak in the awakening hours , and diminish during the day. Circadian prolactin secretion begins in the late afternoon, especially in women, and is subsequently augmented by sleep-induced secretion, to peak in
10395-458: The surface of the brain, under the surface of the dura mater . This is accomplished via burr hole or craniotomy . This is referred to variously as "electrocorticography (ECoG)" , "intracranial EEG (I-EEG)" or "subdural EEG (SD-EEG)". Depth electrodes may also be placed into brain structures, such as the amygdala or hippocampus , structures, which are common epileptic foci and may not be "seen" clearly by scalp EEG. The electrocorticographic signal
10500-561: The table below. Sleep may facilitate the synthesis of molecules that help repair and protect the brain from metabolic end products generated during waking. Anabolic hormones, such as growth hormones , are secreted preferentially during sleep. The brain concentration of glycogen increases during sleep, and is depleted through metabolism during wakefulness. The human organism physically restores itself during sleep, occurring mostly during slow-wave sleep during which body temperature, heart rate, and brain oxygen consumption decrease. In both
10605-421: The trough of the cycle. A healthy young adult entrained to the sun will (during most of the year) fall asleep a few hours after sunset, experience body temperature minimum at 6 a.m., and wake up a few hours after sunrise. Generally speaking, the longer an organism is awake, the more it feels a need to sleep ("sleep debt"). This driver of sleep is referred to as Process S . The balance between sleeping and waking
10710-433: The two is complex, with a combination of EEG power in the gamma band and phase in the delta band relating most strongly to neuron spike activity. In conventional scalp EEG, the recording is obtained by placing electrodes on the scalp with a conductive gel or paste, usually after preparing the scalp area by light abrasion to reduce impedance due to dead skin cells. Many systems typically use electrodes, each of which
10815-420: The various sleep stages ). These oscillations represent synchronized activity over a network of neurons. The neuronal networks underlying some of these oscillations are understood (e.g., the thalamocortical resonance underlying sleep spindles ), while many others are not (e.g., the system that generates the posterior basic rhythm). Research that measures both EEG and neuron spiking finds the relationship between
10920-470: Was analysed using software to identify patterns in the noise. A basic pattern was identified and used to control a switch: Above average activity was set to on, below average off. As well as enabling Jatich to control a computer cursor the signals were also used to drive the nerve controllers embedded in his hands, restoring some movement. In 2018, a functional dry electrode composed of a polydimethylsiloxane elastomer filled with conductive carbon nanofibers
11025-522: Was reported. This research was conducted at the U.S. Army Research Laboratory . EEG technology often involves applying a gel to the scalp which facilitates strong signal-to-noise ratio. This results in more reproducible and reliable experimental results. Since patients dislike having their hair filled with gel, and the lengthy setup requires trained staff on hand, utilizing EEG outside the laboratory setting can be difficult. Additionally, it has been observed that wet electrode sensors' performance reduces after
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