A
delta wave is a high
amplitudeAmplitude 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...
brain wave with a frequency of oscillation between 0–4
hertzThe hertz is the SI unit of frequency defined as the number of cycles per second of a periodic phenomenon. One of its most common uses is the description of the sine wave, particularly those used in radio and audio applications....
. Delta waves, like other brain waves, are recorded with an
electroencephalogramElectroencephalography is the recording of electrical activity along the scalp. EEG measures voltage fluctuations resulting from ionic current flows within the neurons of the brain...
(EEG) and are usually associated with the deepest stages of sleep (3 and 4 NREM), also known as
slow-wave sleepSlow-wave sleep , often referred to as deep sleep, consists of stages 3 and 4 of non-rapid eye movement sleep, according to the Rechtschaffen & Kales standard of 1968. As of 2008, the American Academy of Sleep Medicine has discontinued the use of stage 4, such that the previous stages 3 and 4 now...
(SWS), and aid in characterizing the depth of sleep.
Background and history
"Delta waves" were first described in the early 1900s by W. Grey Walter, who improved upon Dr.
Hans BergerHans Berger was born in Neuses near Coburg, Bavaria, Germany. He is best known as the first to record human electroencephalograms in 1924, for which he invented the electroencephalogram , and the discoverer of the alpha wave rhythm known as "Berger's wave".- Biography :After attending...
's electroencephalograph machine (EEG) to detect alpha and delta waves.
Classification and features
Delta waves, like all brain waves, are detected by
electroencephalographyElectroencephalography is the recording of electrical activity along the scalp. EEG measures voltage fluctuations resulting from ionic current flows within the neurons of the brain...
(EEG). Delta waves were originally defined as having a frequency between 1-4
hertzThe hertz is the SI unit of frequency defined as the number of cycles per second of a periodic phenomenon. One of its most common uses is the description of the sine wave, particularly those used in radio and audio applications....
, although more recent classifications put the boundaries at between 0.5 and 2 hertz. They are the slowest, but highest amplitude brainwaves. Delta waves begin to appear in stage 3 sleep, but by stage 4 nearly all spectral activity is dominated by delta waves. Stage 3 sleep is defined as having less than 50% delta wave activity, while stage 4 sleep has more than 50% delta wave activity. These stages have recently been combined and are now collectively referred to as stage N3 slow-wave sleep. During N3 SWS, delta waves account for 20% or more of the EEG record during this stage. Delta waves occur in all mammals, and potentially all animals as well.
Delta waves are often associated with another EEG phenomenon, the
K-complexA K-complex is an electroencephalography 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...
. K-Complexes have been shown to immediately precede delta waves in slow wave sleep.
Sex differences
Females have been shown to have more delta wave activity, and this is true across most mammal species. This discrepancy does not appear apparent until early adulthood, in the 30's or 40's, in humans, with men showing greater age-related reductions in delta wave activity than their female counterparts. It has been suggested that this discrepancy may be due to larger skull size in males, but this theory has been refuted by intracranial data from female cats, which still show more delta activity.
Brain localization and biochemistry
Delta waves can arise either in the thalamus or in the cortex. When associated with the thalamus, they likely arise in coordination with the
reticular formationThe reticular formation is a part of the brain that is involved in actions such as awaking/sleeping cycle, and filtering incoming stimuli to discriminate irrelevant background stimuli...
. In the cortex, the suprachiasmatic nuclei has been shown to regulate delta waves, as lesions to this area have been shown to cause disruptions in delta wave activity. In addition, delta waves show a lateralization, with right hemisphere dominance during sleep.
Delta waves have been shown to be mediated in part by T-type calcium channels. During delta wave sleep, neurons are globally inhibited by
gamma-aminobutyric acidγ-Aminobutyric acid is the chief inhibitory neurotransmitter in the mammalian central nervous system. It plays a role in regulating neuronal excitability throughout the nervous system...
(GABA).
Delta activity stimulates the release of several hormones, including growth hormone releasing hormone GHRH and
prolactinProlactin also known as luteotropic hormone is a protein that in humans is encoded by the PRL gene.Prolactin is a peptide hormone discovered by Henry Friesen...
(PRL). GHRH is released from the
hypothalamusThe Hypothalamus is a portion of the brain that contains a number of small nuclei with a variety of functions...
, which in turn stimulates release of growth hormone from the pituitary. Like growth hormone, the secretion of prolactin - which is closely related to growth hormone (GH) - is also regulated by the pituitary. Thyroid stimulating hormone (TSH) activity is decreased in response to delta-wave signaling.
Development
Infants have been shown to spend a great deal of time in
slow-wave sleepSlow-wave sleep , often referred to as deep sleep, consists of stages 3 and 4 of non-rapid eye movement sleep, according to the Rechtschaffen & Kales standard of 1968. As of 2008, the American Academy of Sleep Medicine has discontinued the use of stage 4, such that the previous stages 3 and 4 now...
, and thus have more delta wave activity. In fact, delta-waves are the predominant wave forms of infants. Analysis of the waking EEG of a newborn infant indicates that delta wave activity is predominant in that age, and still appears in a waking EEG of five-year-olds. Delta wave activity during slow-wave sleep declines during adolescence, with a drop of around 25% reported between the ages of 11 and 14 years. Delta waves have been shown to decrease across the lifespan, with most of the decline seen in the mid-forties. By the age of about 75, stage four sleep and delta waves may be entirely absent.
In addition to a decrease in the incidence of delta waves during slow-wave sleep in the elderly, the incidence of temporal delta wave activity is common seen in older adults, and incidences also increase with age.
Disruptions and disorders
Regional delta wave activity not associated with NREM sleep was first described by W. Grey Walter, who studied cerebral hemisphere tumors. Disruptions in delta wave activity and slow wave sleep are seen in a wide array of disorders. In some cases there may be increases or decreases in delta wave activity, while others may manifest as disruptions in delta wave activity, such as alpha waves presenting in the EEG spectrum. Delta wave disruptions may present as a result of physiological damage, changes in nutrient metabolism, chemical alteration, or may also be idiopathic.
Disruptions in delta activity is seen in adults during states of intoxication or
deliriumDelirium or acute confusional state is a common and severe neuropsychiatric syndrome with core features of acute onset and fluctuating course, attentional deficits and generalized severe disorganization of behavior...
and in those diagnosed with various neurological disorders such as
dementiaDementia is a serious loss of cognitive ability in a previously unimpaired person, beyond what might be expected from normal aging...
or
schizophreniaSchizophrenia is a mental disorder characterized by a disintegration of thought processes and of emotional responsiveness. It most commonly manifests itself as auditory hallucinations, paranoid or bizarre delusions, or disorganized speech and thinking, and it is accompanied by significant social...
.
Temporal Low-voltage Irregular Delta Wave (TLID)
Temporal low-voltage irregular delta wave activity has been commonly detected in patients with ischemic brain diseases. In addition, small ischemic lesions have been shown to be closely correlated with TLID, and are indicative of early-stage cerebrovasular damage.
Parasomnias
Parasomnias are often associated with disruptions in slow wave sleep. Sleep walking and sleep talking most often occur during periods of high-delta wave activity. Sleep walkers have also been shown to have more Hypersynchronous Delta Activity (HSD activity) compared to total time spent in stages 2, 3, and 4 sleep relative to healthy controls.
Hypersynchronous Delta Activity (HSD) are continuous, high-voltage (> 150 uV) delta waves seen in sleep EEGs. Parasomnias which occur deep in NREM sleep also include sleep terrors and confusional arousals.
Sleep deprivation
Total sleep deprivation has been shown to increase delta wave activity during sleep recovery, and has also been shown to increase hypersynchronous delta activity (HSD).
Parkinson's disease
Sleep disturbances, as well as dementia, are common features of
Parkinson's diseaseParkinson's disease is a degenerative disorder of the central nervous system...
, and patients with PD show disrupted brain wave activity. The drug rotigotine, developed for PD, has been shown to increase delta power and slow-wave sleep in those with Parkinson's disease. Interestingly, delta-wave inducing peptide injected into the
substantia nigraThe substantia nigra is a brain structure located in the mesencephalon that plays an important role in reward, addiction, and movement. Substantia nigra is Latin for "black substance", as parts of the substantia nigra appear darker than neighboring areas due to high levels of melanin in...
of the rat model has been shown to increase parkinsonian symptoms.
Schizophrenia
People suffering schizophrenia have shown disrupted EEG patterns, and there is a close association of reduced delta waves during deep sleep and negative symptoms associated with
schizophreniaSchizophrenia is a mental disorder characterized by a disintegration of thought processes and of emotional responsiveness. It most commonly manifests itself as auditory hallucinations, paranoid or bizarre delusions, or disorganized speech and thinking, and it is accompanied by significant social...
. During slow wave sleep (stages 3 and 4), schizophrenics have been shown to have reduced delta wave activity, although delta waves have also been shown to be increased during waking hours in more severe forms of schizophrenia.
A recent study has shown that the right frontal and central delta wave dominance, seen in healthy individuals, is absent in schizophrenics. In addition, the negative correlation between delta wave activity and age is also not observed in those with schizophrenia.
Diabetes and insulin resistance
Disruptions in slow wave (delta) sleep have been shown to increase risk for development of Type II diabetes, potentially due to disruptions in the growth hormone secreted by the pituitary. In addition, hypoglycemia occurring during sleep may also disrupt delta-wave activity. Low-voltage irregular delta waves (TLID) have also been found in the left temporal lobe of diabetic patients, at a rate of 56% (compared to 14% in healthy controls).
Fibromyalgia
Patients suffering from
fibromyalgiaFibromyalgia is a medical disorder characterized by chronic widespread pain and allodynia, a heightened and painful response to pressure. It is an example of a diagnosis of exclusion...
often report unrefreshing sleep. A study conducted in 1975 by Moldovsky
et al. showed that the delta wave activity of these patients in stages 3 and 4 sleep were often interrupted by
alpha waveAlpha waves are neural oscillations in the frequency range of 8–12 Hz arising from synchronous and coherent electrical activity of thalamic pacemaker cells in humans...
s. They later showed that depriving the body of delta wave sleep activity also induced musculoskeletal pain and fatigue.
Alcoholism
Alcohol has been shown to decrease slow wave sleep and delta power, while increasing stage 1 and REM incidence in both men and women. In long-term alcohol abuse, the influences of alcohol on sleep architecture and reductions in delta activity have been shown to persist even after long periods of abstinence.
Temporal lobe epilepsy
Slow waves, including delta waves, are associated with seizure-like activity within the brain.
W. Grey Walter was the first person to use delta waves from an EEG to locate brain tumors and lesions causing temporal lobe epilepsy.
NeurofeedbackNeurofeedback , also called neurotherapy, neurobiofeedback or EEG biofeedback is a type of biofeedback that uses realtime displays of electroencephalography or functional magnetic resonance imaging to illustrate brain activity, often with a goal of controlling central nervous system activity...
has been suggested as a treatment for temporal lobe epilepsy, and theoretically acts to reduce inappropriate delta wave intrusion, although there has been limited clinical research in this area.
Other disorders
Other disorders frequently associated with disrupted delta-wave activity include:
- depression
- anxiety
- obsessive-compulsive disorder
- attention deficit disorder (ADD)/ attention deficit hyperactivity disorder (ADHD)
- juvenile chronic arthritis
Consciousness and dreaming
Initially, dreaming was thought to only occur in rapid eye movement sleep, though it is now known that dreaming may also occur during slow-wave sleep. Delta waves and delta wave activity are marked by an unconscious state, and the loss of physical awareness as well as the "iteration of information". Delta wave activity has also been purported to aid in the formation of declarative and explicit memory formation.
Pharmacology
While most drugs that affect sleep do so by stimulating sleep onset, or disrupting REM sleep, a number of chemicals and drugs have been shown to alter delta wave activity.
- Delta sleep-inducing peptide
Delta sleep-inducing peptide, abbreviated DSIP, is a neuropeptide that when infused into the mesodiencephalic ventricle ofrecipient rabbits induces spindle and delta EEG activity and reduced motor activities....
, as the name suggests, induces delta wave EEG activity.
- Alcohol reduces SWS delta wave activity, thereby restricting the release of growth hormone
Growth hormone is a peptide hormone that stimulates growth, cell reproduction and regeneration in humans and other animals. Growth hormone is a 191-amino acid, single-chain polypeptide that is synthesized, stored, and secreted by the somatotroph cells within the lateral wings of the anterior...
(GH) by the pituitary.
- The muramyl peptide, muramyl dipeptide (MDP, N-acetylmuramyl-L-alanyl-D-isoglutamine) has been shown to increase delta wave activity during slow wave sleep.
- The drug Gabapentin
Gabapentin is a pharmaceutical drug, specifically a GABA analogue. It was originally developed for the treatment of epilepsy, and currently is also used to relieve neuropathic pain...
, a drug used to control epileptic seizures, increases delta-wave activity and slow wave sleep in adults.
- While hypnotic drugs increase slow wave sleep, they do not increase delta wave activity, and instead increase spindle activity during slow wave sleep.
- Gabba-hydroxy butyrate (GHB) increases delta slow-wave sleep as well as sleep-related growth hormone (GH).
Effects of diet
Diets very low in carbohydrates, such as a
ketogenic dietThe ketogenic diet is a high-fat, adequate-protein, low-carbohydrate diet that in medicine is used primarily to treat difficult-to-control epilepsy in children. The diet mimics aspects of starvation by forcing the body to burn fats rather than carbohydrates...
, have been shown to increase the amount of delta activity and slow wave sleep in healthy individuals.
See also
- Holonomic brain theory
The holonomic brain theory, originated by psychologist Karl Pribram and initially developed in collaboration with physicist David Bohm, is a model for human cognition that is drastically different from conventionally accepted ideas: Pribram and Bohm posit a model of cognitive function as being...
- Sensorimotor rhythm
- Description :The Sensory Motor Rhythm is brain wave rhythm. It is an oscillatory idle rhythm of synchronized electromagnetic brain activity. It appears in spindles in recordings of EEG, MEG, and ECoG over the sensorimotor cortex. For most individuals, the frequency of the SMR is in the range...
- Wolff-Parkinson-White syndrome
Wolff–Parkinson–White syndrome is a disorder of the heart in which the ventricles of the heart contract prematurely due to an accessory pathway known as the bundle of Kent. This accessory pathway is an abnormal electrical communication from the atria to the ventricles...
- slow-wave sleep
Slow-wave sleep , often referred to as deep sleep, consists of stages 3 and 4 of non-rapid eye movement sleep, according to the Rechtschaffen & Kales standard of 1968. As of 2008, the American Academy of Sleep Medicine has discontinued the use of stage 4, such that the previous stages 3 and 4 now...
- K-complex
A K-complex is an electroencephalography 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...
- 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...
- Delta sleep-inducing peptide
Delta sleep-inducing peptide, abbreviated DSIP, is a neuropeptide that when infused into the mesodiencephalic ventricle ofrecipient rabbits induces spindle and delta EEG activity and reduced motor activities....
Other brain waves
- Theta wave – (4–7 Hz)
- Alpha wave
Alpha waves are neural oscillations in the frequency range of 8–12 Hz arising from synchronous and coherent electrical activity of thalamic pacemaker cells in humans...
– (8–12 Hz)
- Mu wave
Mu waves, also known as the comb or wicket rhythm, are electromagnetic oscillations in the frequency range of 8–13 Hz and appear in bursts of at 9 – 11 Hz. Mu wave patterns arise from synchronous and coherent electrical activity of large groups of neurons in the human brain...
– (8–13 Hz)
- Beta wave
Beta wave, or beta rhythm, is the term used to designate the frequency range of human brain activity between 12 and 30 Hz . Beta waves are split into three sections: High Beta Waves ; Beta Waves ; and Low Beta Waves...
– (12–30 Hz)
- 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...
– (25–100 Hz)