K-complex
Encyclopedia
A K-complex is an electroencephalography (EEG)
waveform that occurs during stage 2 of NREM sleep. It is the "largest event in healthy human EEG". They are more frequent in the first sleep cycles of sleep.
K-complexes have two proposed functions. First, suppressing cortical arousal in response to stimuli that the sleeping brain evaluates not to signal danger, and second, aiding sleep-based memory consolidation
.
The K-complex was discovered in 1937 in the private laboratories of Alfred Lee Loomis
.
s. They occur spontaneously but also occur in response to external stimuli such as sounds, touches on the skin and internal ones such as inspiratory interruptions. They are generated in widespread cortical locations though they tend to predominate over the frontal parts of the brain.
Both K-complex and delta wave
activity in stage 2 sleep create slow wave (0.8 Hz) oscillation and delta (1.6–4.0 Hz). However, their topographical distribution is different, and the delta power of K-complexes is higher.
They are created by the occurrence in widespread cortical areas of outward dendritic currents from the middle (III) to the upper (I) layers of the cerebral cortex
. This is accompanied by a decrease in broadband EEG power including gamma wave
activity. This produces "down-states" of neuronal silence in which neural network activity is reduced. The activity of K-complexes is transferred to the thalamus
where it synchronizes the thalamocortical network during sleep, producing sleep oscillations such as spindles and delta wave
s. It has been observed that they are indeed identical in the "laminar distributions of transmembrane currents" to the slow waves of slow wave sleep.
K-complexes have been suggested both to protect sleep and also to engage in information processing as they are both an essential part of the synchronization of NREM sleep while they also respond to both internal and external stimuli in a reactive manner. This would be consistent with a function in suppressing cortical arousal in response to stimuli that the brain needs to initially process in regard to whether it is dangerous or not.
Another suggested function is aiding the activation homeostasis
of synapse
s and memory consolidation. The activation thresholds of cortical synapses become raised during wakefulness as they process information, and so need to be adjusted back to preserve their signal-to-noise ratio. The down-state provided by K-complexes does this by reducing the strengths of synaptic connections that occur when they are activated while an individual is awake. Further, the recovery from the down-state they induce allows that "cortical firing 'reboots' in a systematic order" so that memory engrams encoded during neuronal firing can be "repeatedly practiced and thus consolidated".
s, and develop with age. Between 3 and 5 years of age a faster negative component appears and continues to increase until adolescence
. Another change occurs in adults: before 30 years of age their frequency
and amplitude
is higher than in older people particularly those over 50 years of age. This parallels the decrease in other components of sleep such as sleep spindle density and delta power
.
, K-complex induced synchronization
can trigger spike-wave discharges. This tends to happen most between the shift between waking and NREM, and between NREM and REM sleep. In autosomal dominant nocturnal frontal lobe epilepsy
, K-complexes are almost invariably present at the start of seizures.
have increased numbers of K-complexes and these are associated with (and often precede) leg movements. Dopamine
enhancing drugs such as L-DOPA that reduce leg movements do not reduce the K-complex suggesting that they are primary and the leg movements secondary to them. Failure of such drugs to reduce K-complexes in spite of reducing the leg movements has been suggested to be why patients after such treatment still continue to complain of non-restorative sleep. Clonazepam
is another treatment for RLS; like other benzodiazepines, it inhibits REM sleep by enhancing levels of GABA
. This inhibition of REM sleep significantly decreases K-complex count, and unlike L-DOPA treatment, clonazepam studies report improvement in sleep restoration. Therefore, drugs that inhibit REM sleep also decrease K-complex count.
syndrome is associated with inspiratory occlusions evoking fewer K-complexes during NREM sleep even though K-complexes are evoked normally to auditory stimuli and such individuals react normally to respiratory interruptions when awake. This suggests a link between such sleep apnea and a sleep specific blunted cortical response to respiratory problems.
Electroencephalography
Electroencephalography is the recording of electrical activity along the scalp. EEG measures voltage fluctuations resulting from ionic current flows within the neurons of the brain...
waveform that occurs during stage 2 of NREM sleep. It is the "largest event in healthy human EEG". They are more frequent in the first sleep cycles of sleep.
K-complexes have two proposed functions. First, suppressing cortical arousal in response to stimuli that the sleeping brain evaluates not to signal danger, and second, aiding sleep-based memory consolidation
Memory consolidation
Memory consolidation is a category of processes that stabilize a memory trace after the initial acquisition. Consolidation is distinguished into two specific processes, synaptic consolidation, which occurs within the first few hours after learning, and system consolidation, where...
.
The K-complex was discovered in 1937 in the private laboratories of Alfred Lee Loomis
Alfred Lee Loomis
Alfred Lee Loomis was an American attorney, investment banker, philanthropist, scientist/physicist, pioneer in military radar usages, inventor of the LORAN or Long Range Navigation System, and lifelong patron of scientific research...
.
Neurophysiology
K-complex consists of a brief negative high-voltage peak, usually greater than 100 µV, followed by a slower positive complex around 350 and 550 ms and at 900 ms a final negative peak. K-complexes occur roughly every 1.0–1.7 minutes and are often followed by bursts of sleep spindleSleep spindle
A sleep spindle is a burst of brain activity visible on an EEG that occurs during stage 2 sleep. It consists of 12–14 Hz waves that occur for at least 0.5 seconds.-Function:...
s. They occur spontaneously but also occur in response to external stimuli such as sounds, touches on the skin and internal ones such as inspiratory interruptions. They are generated in widespread cortical locations though they tend to predominate over the frontal parts of the brain.
Both K-complex and delta wave
Delta wave
A delta wave is a high amplitude brain wave with a frequency of oscillation between 0–4 hertz. Delta waves, like other brain waves, are recorded with an electroencephalogram and are usually associated with the deepest stages of sleep , also known as slow-wave sleep , and aid in characterizing the...
activity in stage 2 sleep create slow wave (0.8 Hz) oscillation and delta (1.6–4.0 Hz). However, their topographical distribution is different, and the delta power of K-complexes is higher.
They are created by the occurrence in widespread cortical areas of outward dendritic currents from the middle (III) to the upper (I) layers of the cerebral cortex
Cerebral cortex
The cerebral cortex is a sheet of neural tissue that is outermost to the cerebrum of the mammalian brain. It plays a key role in memory, attention, perceptual awareness, thought, language, and consciousness. It is constituted of up to six horizontal layers, each of which has a different...
. This is accompanied by a decrease in broadband EEG power including gamma wave
Gamma wave
A gamma wave is a pattern of neural oscillation in humans with a frequency between 25 to 100 Hz, though 40 Hz is prototypical.According to a popular theory, gamma waves may be implicated in creating the unity of conscious perception...
activity. This produces "down-states" of neuronal silence in which neural network activity is reduced. The activity of K-complexes is transferred to the thalamus
Thalamus
The thalamus is a midline paired symmetrical structure within the brains of vertebrates, including humans. It is situated between the cerebral cortex and midbrain, both in terms of location and neurological connections...
where it synchronizes the thalamocortical network during sleep, producing sleep oscillations such as spindles and delta wave
Delta wave
A delta wave is a high amplitude brain wave with a frequency of oscillation between 0–4 hertz. Delta waves, like other brain waves, are recorded with an electroencephalogram and are usually associated with the deepest stages of sleep , also known as slow-wave sleep , and aid in characterizing the...
s. It has been observed that they are indeed identical in the "laminar distributions of transmembrane currents" to the slow waves of slow wave sleep.
K-complexes have been suggested both to protect sleep and also to engage in information processing as they are both an essential part of the synchronization of NREM sleep while they also respond to both internal and external stimuli in a reactive manner. This would be consistent with a function in suppressing cortical arousal in response to stimuli that the brain needs to initially process in regard to whether it is dangerous or not.
Another suggested function is aiding the activation homeostasis
Homeostasis
Homeostasis is the property of a system that regulates its internal environment and tends to maintain a stable, constant condition of properties like temperature or pH...
of synapse
Synapse
In the nervous system, a synapse is a structure that permits a neuron to pass an electrical or chemical signal to another cell...
s and memory consolidation. The activation thresholds of cortical synapses become raised during wakefulness as they process information, and so need to be adjusted back to preserve their signal-to-noise ratio. The down-state provided by K-complexes does this by reducing the strengths of synaptic connections that occur when they are activated while an individual is awake. Further, the recovery from the down-state they induce allows that "cortical firing 'reboots' in a systematic order" so that memory engrams encoded during neuronal firing can be "repeatedly practiced and thus consolidated".
Development
They are present in the sleep of 5-month-old infantInfant
A newborn or baby is the very young offspring of a human or other mammal. A newborn is an infant who is within hours, days, or up to a few weeks from birth. In medical contexts, newborn or neonate refers to an infant in the first 28 days after birth...
s, and develop with age. Between 3 and 5 years of age a faster negative component appears and continues to increase until adolescence
Adolescence
Adolescence is a transitional stage of physical and mental human development generally occurring between puberty and legal adulthood , but largely characterized as beginning and ending with the teenage stage...
. Another change occurs in adults: before 30 years of age their frequency
Frequency
Frequency is the number of occurrences of a repeating event per unit time. It is also referred to as temporal frequency.The period is the duration of one cycle in a repeating event, so the period is the reciprocal of the frequency...
and amplitude
Amplitude
Amplitude is the magnitude of change in the oscillating variable with each oscillation within an oscillating system. For example, sound waves in air are oscillations in atmospheric pressure and their amplitudes are proportional to the change in pressure during one oscillation...
is higher than in older people particularly those over 50 years of age. This parallels the decrease in other components of sleep such as sleep spindle density and delta power
Delta wave
A delta wave is a high amplitude brain wave with a frequency of oscillation between 0–4 hertz. Delta waves, like other brain waves, are recorded with an electroencephalogram and are usually associated with the deepest stages of sleep , also known as slow-wave sleep , and aid in characterizing the...
.
Epilepsy
In individuals with idiopathic generalized epilepsyIdiopathic generalized epilepsy
Idiopathic generalized epilepsy is a group of epileptic disorders that are believed to have a strong underlying genetic basis. Patients with an IGE subtype are typically otherwise normal and have no anatomical brain abnormalities. Patients also often have a family history of epilepsy and seem to...
, K-complex induced synchronization
Neural oscillations
Neural oscillation is rhythmic or repetitive neural activity in the central nervous system. Neural tissue can generate oscillatory activity in many ways, driven either by mechanisms localized within individual neurons or by interactions between neurons...
can trigger spike-wave discharges. This tends to happen most between the shift between waking and NREM, and between NREM and REM sleep. In autosomal dominant nocturnal frontal lobe epilepsy
Autosomal dominant nocturnal frontal lobe epilepsy
Autosomal dominant nocturnal frontal lobe epilepsy is a rare epileptic disorder that causes frequent violent seizures during sleep. These seizures often involve complex motor movements, such as hand clenching, arm raising/lowering, and knee bending. Vocalizations such as shouting, moaning, or...
, K-complexes are almost invariably present at the start of seizures.
Restless legs syndrome
Individuals with restless legs syndromeRestless legs syndrome
Restless legs syndrome or Willis-Ekbom disease is a neurological disorder characterized by an irresistible urge to move one's body to stop uncomfortable or odd sensations. It most commonly affects the legs, but can affect the arms, torso, and even phantom limbs...
have increased numbers of K-complexes and these are associated with (and often precede) leg movements. Dopamine
Dopamine
Dopamine is a catecholamine neurotransmitter present in a wide variety of animals, including both vertebrates and invertebrates. In the brain, this substituted phenethylamine functions as a neurotransmitter, activating the five known types of dopamine receptors—D1, D2, D3, D4, and D5—and their...
enhancing drugs such as L-DOPA that reduce leg movements do not reduce the K-complex suggesting that they are primary and the leg movements secondary to them. Failure of such drugs to reduce K-complexes in spite of reducing the leg movements has been suggested to be why patients after such treatment still continue to complain of non-restorative sleep. Clonazepam
Clonazepam
Clonazepamis a benzodiazepine drug having anxiolytic, anticonvulsant, muscle relaxant, and hypnotic properties. It is marketed by Roche under the trade name Klonopin in the United States and Rivotril in Australia, Brazil, Canada and Europe...
is another treatment for RLS; like other benzodiazepines, it inhibits REM sleep by enhancing levels of GABA
Gabâ
Gabâ or gabaa, for the people in many parts of the Philippines), is the concept of a non-human and non-divine, imminent retribution. A sort of negative karma, it is generally seen as an evil effect on a person because of their wrongdoings or transgressions...
. This inhibition of REM sleep significantly decreases K-complex count, and unlike L-DOPA treatment, clonazepam studies report improvement in sleep restoration. Therefore, drugs that inhibit REM sleep also decrease K-complex count.
Obstructive sleep apnea
Obstructive sleep apneaObstructive sleep apnea
Obstructive sleep apnea or obstructive sleep apnea syndrome is the most common type of sleep apnea and is caused by obstruction of the upper airway. It is characterized by repetitive pauses in breathing during sleep, despite the effort to breathe, and is usually associated with a reduction in...
syndrome is associated with inspiratory occlusions evoking fewer K-complexes during NREM sleep even though K-complexes are evoked normally to auditory stimuli and such individuals react normally to respiratory interruptions when awake. This suggests a link between such sleep apnea and a sleep specific blunted cortical response to respiratory problems.