PGO waves
Encyclopedia
Ponto-geniculo-occipital waves or PGO waves are phasic field potentials. These waves can be recorded from the pons
, the lateral geniculate nucleus
(LGN), and the occipital cortex regions of the brain, where these waveforms originate. The waves begin as electrical pulses from the pons, then move to the lateral geniculate nucleus residing in the thalamus
, and then finally end up in the primary visual cortex of the occipital lobe. The appearances of these waves are most prominent in the period right before rapid eye movement sleep (or REM sleep), and are theorized to be intricately involved with eye movement of both wake and sleep cycles in many different animals.
. Although at this time, they did not have a specific name for this neurological phenomenon.
It was not until the published work of two American scientists that these waves became known as PGO waves. Their research focused on the propagation of these waves in cats, noticing that these field potentials started in the pons, propagating down to the lateral geniculate nucleus and the occipital lobe.
Other studies with these waves have been done on rats as well. Scientists tried to discern whether the rats had PGO waves, but learned that they are only present in the pons and wave propagation does not excite any neurons in the lateral geniculate nucleus. As a result of this study, PGO waves are known as P waves in rodents.
PGO waves have been mostly studied through cat and rodent animal models. Despite the focus of the research, PGO waves have been found to exist in other mammalian species including humans and nonhuman primates, such as the macaque and baboon.
(EEG) recording techniques, scientists are also able to show the correlation between other brain waves associated with REM sleep and PGO waves.
Although scientists know they exist, PGO waves have not been detected in healthy humans due to the ethical concerns about accessing these areas where the readings need to be taken from. However, advances in deep brain stimulation
has made it possible to put electrodes inside the brains of humans with different pathologies and make EEG recordings of different nuclei. Due to the similarities with the animal models, we can infer that PGO waves are happening at the same frequency in human EEGs. Thus, scientists can infer that PGO waves exist in humans.
s branch out in a network that leads the phasic electrical signal toward the lateral geniculate nucleus and the occipital lobe.
Within this network, there are two types of neuronal groups: executive neurons and modulatory neurons.
During the times when triggering neurons are firing, these cells receive those signals and begin increasing their firing. This, in turn, allows the wave to go out to the other portions of the brain.
as a neurotransmitter
. This class of neurotransmitters is what keeps PGO wave amplitudes at very low levels during periods of a mammal being awake. The two specific aminergic neutransmitters are serotonin
and norepinephrine
.
are neurons that use acetylcholine
as a neurotransmitter. Through different studies, these types of neurons have been proven to promote PGO wave generation, thus being an excitatory neuromodulator for triggering neurons.
(NO) as a neurotrasmitter. Theoretically, the increase of nitric oxide is seen as an excitatory neuromodulator in PGO wave generation. This stems from animal testing that has shown increases in PGO waves as nitric oxide levels were increased in the pons.
(GABA) as a neurotransmitter. These neurons are theorized to be inhibitory to aminergic neurons, and thus inhibitory to PGO wave propagation.
region of the brain have been shown to provide excitatory bouts of PGO wave generation when stimulated. The tests showed that while the vestibular nuclei aided in creating PGO waves, the excitation of this area of the brain was in no way needed for PGO wave formation.
region of the brain have also been shown to provide excitatory bouts of PGO wave generation when electrically stimulated.
are a group of nuclei in the brains of vertebrates, situated at the base of the forebrain and strongly connected with the cerebral cortex, thalamus and pons. The basal ganglia are associated with a variety of functions, including arousal, motor control and learning. The main components of the basal ganglia are the striatum, pallidum, substantia nigra, and subthalamic nucleus
(or subthalamus). This latter, glutamatergic nucleus is reciprocally connected with the PGO-transferring nuclei of the pons
. In humans, subthalamic PGO-like waves, that resemble the PGO waves typically recorded in cats, can be recorded during pre-REM and REM sleep. This suggests that the subthalamus may play an active role in an ascending activating network implicated in the rostral transmission of PGO waves during REM sleep in humans.
One key use of REM sleep is for the brain to process and store information from the previous day. In a sense, the brain is learning by establishing new neuronal connections for things that have been learned. Neurophysiological studies have indicated a relationship between increased P-wave density during post-training REM sleep and learning performance. Basically, the abundance of PGO waves translates into longer periods of REM sleep, which thereby allows the brain to have longer periods where neuronal connections are formed.
The importance of PGO waves during REM sleep also aids the idea of PGO waves being a signal that a person is dreaming. Since dreaming occurs during REM sleep, the PGO waves are theorized to be the signals that make the brain start to recount the experiences from the previous day. This, in turn, allows us to "see" our dreams since our visual sense is quickly going through the information it has stored.
For more information of the importance of PGO waves during REM sleep, please refer to Activation synthesis theory.
The next big area to research regarding this topic is to understand what processes PGO waves are beneficial for in both states of sleep as well as consciousness. Although PGO waves are noticeably present during NREM sleep, some scientists believe they are also present during waking cycles. There is a possibility that PGO waves are essential for image correction of the eyes, since PGO waves are signals on a pathway that allow the motor cortex of the brain to interface with the vision system.
The other future interests in research of this topic are what PGO waves are precisely doing for us while we are dreaming. Some scientists theorize that PGO waves are essential for stabilizing the images that we have in our dreams. This theory comes from the eye movements that coincide with the readings from electrodes picking up PGO waves.
Also, scientists seek to discover how the presence of these signals fits in with the overall dreaming process. Current trends in neurophysiology tend to focus on cell to cell connections of neurons, but many know that we still need to research the bigger picture ideas of this field of research. The importance of PGO waves is one of those broad approaches to neurophysiology because it involves the coordination of entire regions of the brain to work together—coming from many different systems—to create our dreams, memories, and other experiences that we have.
Another area of research interest would be to look at PGO waves during lucid dreaming, since the brain is both asleep and awake at the very same time.
Pons
The pons is a structure located on the brain stem, named after the Latin word for "bridge" or the 16th-century Italian anatomist and surgeon Costanzo Varolio . It is superior to the medulla oblongata, inferior to the midbrain, and ventral to the cerebellum. In humans and other bipeds this means it...
, the lateral geniculate nucleus
Lateral geniculate nucleus
The lateral geniculate nucleus is the primary relay center for visual information received from the retina of the eye. The LGN is found inside the thalamus of the brain....
(LGN), and the occipital cortex regions of the brain, where these waveforms originate. The waves begin as electrical pulses from the pons, then move to the lateral geniculate nucleus residing in 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...
, and then finally end up in the primary visual cortex of the occipital lobe. The appearances of these waves are most prominent in the period right before rapid eye movement sleep (or REM sleep), and are theorized to be intricately involved with eye movement of both wake and sleep cycles in many different animals.
Discovery
The discovery of PGO waves goes back to 1959, when three French scientists released their scientific article of their study of these waves in animal test subjectsAnimal model
An animal model is a living, non-human animal used during the research and investigation of human disease, for the purpose of better understanding the disease without the added risk of causing harm to an actual human being during the process...
. Although at this time, they did not have a specific name for this neurological phenomenon.
It was not until the published work of two American scientists that these waves became known as PGO waves. Their research focused on the propagation of these waves in cats, noticing that these field potentials started in the pons, propagating down to the lateral geniculate nucleus and the occipital lobe.
Other studies with these waves have been done on rats as well. Scientists tried to discern whether the rats had PGO waves, but learned that they are only present in the pons and wave propagation does not excite any neurons in the lateral geniculate nucleus. As a result of this study, PGO waves are known as P waves in rodents.
PGO waves have been mostly studied through cat and rodent animal models. Despite the focus of the research, PGO waves have been found to exist in other mammalian species including humans and nonhuman primates, such as the macaque and baboon.
Detection of PGO waves
In the original experiments, PGO waves (or P waves in rodent models) are found by placing electrodes inside the brain, next to either the pons, lateral geniculate nuclei, or occipital lobe. Along with electroencephalographyElectroencephalography
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...
(EEG) recording techniques, scientists are also able to show the correlation between other brain waves associated with REM sleep and PGO waves.
Although scientists know they exist, PGO waves have not been detected in healthy humans due to the ethical concerns about accessing these areas where the readings need to be taken from. However, advances in deep brain stimulation
Deep brain stimulation
Deep brain stimulation is a surgical treatment involving the implantation of a medical device called a brain pacemaker, which sends electrical impulses to specific parts of the brain...
has made it possible to put electrodes inside the brains of humans with different pathologies and make EEG recordings of different nuclei. Due to the similarities with the animal models, we can infer that PGO waves are happening at the same frequency in human EEGs. Thus, scientists can infer that PGO waves exist in humans.
Mechanism for PGO wave generation and propagation
The neurophysiological studies on PGO waves conclude that the generation of these waves reside in a collection of neurons located in the pons, regardless of species research is done on. From this point, the neuronNeuron
A neuron is an electrically excitable cell that processes and transmits information by electrical and chemical signaling. Chemical signaling occurs via synapses, specialized connections with other cells. Neurons connect to each other to form networks. Neurons are the core components of the nervous...
s branch out in a network that leads the phasic electrical signal toward the lateral geniculate nucleus and the occipital lobe.
Within this network, there are two types of neuronal groups: executive neurons and modulatory neurons.
Executive neurons
These neurons are the ones that help to generate and propagate the PGO waves throughout the brain. One research paper further breaks down this "class" of neurons into two subsets: triggering neurons and transfer neurons. All of these neurons are located in the peribrachial area, which is a group of neurons surrounding the superior cerebellar penduncle.Triggering neurons
These neurons are located in the caudolateral region of the peribrachial area. These neurons actively fire during non-REM (NREM) sleep. The most recorded activity of the neurons is during the N3 stage of NREM, also known as the slow-wave sleep cycle. These same neurons are also active during REM sleep, but at a greatly reduced amplitude than NREM sleep.Transfer neurons
The neuronal cells that allow for the transfer of PGO waves from the pons to the other parts of the brain reside on the rostral portion of the peribrachial area. This grouping of cells fire in precisely two modes. The first mode is burst firing through low-threshold Calcium (Ca2+) ion channels. The other mode is a repetitive tonic firing through Sodium (Na+) dependent ion channels.During the times when triggering neurons are firing, these cells receive those signals and begin increasing their firing. This, in turn, allows the wave to go out to the other portions of the brain.
Modulatory neurons
As the executive neurons are firing, the spread of the wave is controlled by both excitatory and inhibitory inputs. These inputs come from the modulatory neurons, which help to regulate and control the amplitude and frequency of the wave. The following types of cells play a huge part in this control process.Aminergic neurons
Aminergic neurons are neurons that use monoaminesMonoamine neurotransmitter
thumb|right|350px| A phylogenetic tree showing how a number of monoamine receptors are related to each other.Monoamine neurotransmitters are neurotransmitters and neuromodulators that contain one amino group that is connected to an aromatic ring by a two-carbon chain...
as a neurotransmitter
Neurotransmitter
Neurotransmitters are endogenous chemicals that transmit signals from a neuron to a target cell across a synapse. Neurotransmitters are packaged into synaptic vesicles clustered beneath the membrane on the presynaptic side of a synapse, and are released into the synaptic cleft, where they bind to...
. This class of neurotransmitters is what keeps PGO wave amplitudes at very low levels during periods of a mammal being awake. The two specific aminergic neutransmitters are serotonin
Serotonin
Serotonin or 5-hydroxytryptamine is a monoamine neurotransmitter. Biochemically derived from tryptophan, serotonin is primarily found in the gastrointestinal tract, platelets, and in the central nervous system of animals including humans...
and norepinephrine
Norepinephrine
Norepinephrine is the US name for noradrenaline , a catecholamine with multiple roles including as a hormone and a neurotransmitter...
.
Cholinergic neurons
Cholinergic neuronsCholinergic
The word choline generally refers to the various quaternary ammonium salts containing the N,N,N-trimethylethanolammonium cation. Found in most animal tissues, choline is a primary component of the neurotransmitter acetylcholine and functions with inositol as a basic constituent of lecithin...
are neurons that use acetylcholine
Acetylcholine
The chemical compound acetylcholine is a neurotransmitter in both the peripheral nervous system and central nervous system in many organisms including humans...
as a neurotransmitter. Through different studies, these types of neurons have been proven to promote PGO wave generation, thus being an excitatory neuromodulator for triggering neurons.
Nitroxergic neurons
Nitroxergic neurons use nitric oxideNitric oxide
Nitric oxide, also known as nitrogen monoxide, is a diatomic molecule with chemical formula NO. It is a free radical and is an important intermediate in the chemical industry...
(NO) as a neurotrasmitter. Theoretically, the increase of nitric oxide is seen as an excitatory neuromodulator in PGO wave generation. This stems from animal testing that has shown increases in PGO waves as nitric oxide levels were increased in the pons.
GABA-ergic neurons
GABA-ergic neurons use gamma-aminobutyric acidGamma-aminobutyric acid
γ-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) as a neurotransmitter. These neurons are theorized to be inhibitory to aminergic neurons, and thus inhibitory to PGO wave propagation.
Vestibular nuclei
The neurons within the vestibular nucleiVestibular nuclei
The vestibular nuclei are the cranial nuclei for the vestibular nerve.In Terminologia Anatomica they are grouped in both the pons and medulla.-Subnuclei:There are 4 subnuclei; they are situated at the floor of the fourth ventricle....
region of the brain have been shown to provide excitatory bouts of PGO wave generation when stimulated. The tests showed that while the vestibular nuclei aided in creating PGO waves, the excitation of this area of the brain was in no way needed for PGO wave formation.
Amygdala
The neurons within the amygdalaAmygdala
The ' are almond-shaped groups of nuclei located deep within the medial temporal lobes of the brain in complex vertebrates, including humans. Shown in research to perform a primary role in the processing and memory of emotional reactions, the amygdalae are considered part of the limbic system.-...
region of the brain have also been shown to provide excitatory bouts of PGO wave generation when electrically stimulated.
Suprachiasmatic nuclei
The neurons within the suprachiasmatic nuclei region of the brain help to regulate REM sleep. The REM sleep cycle length causes the frequency of PGO waves to be phase locked.Auditory stimulation
The use of auditory stimulation has been shown to increase PGO waves during waking and sleeping cycles with neurons associated with transfers of auditory information. Even while the subject is awake and in total darkness, the amplitude of PGO waves increases by auditory stimulation. Another study also found that auditory stimulation increased the amplitude of PGO waves in slow-wave sleep and REM sleep and did not reduce the amplitude of the waves with repeated auditory stimulation. From this research, scientists can theorize that PGO wave generation from auditory stimulation contains a positive-feedback mechanism which can be excited by evoked PGO waves.Basal ganglia
The basal gangliaBasal ganglia
The basal ganglia are a group of nuclei of varied origin in the brains of vertebrates that act as a cohesive functional unit. They are situated at the base of the forebrain and are strongly connected with the cerebral cortex, thalamus and other brain areas...
are a group of nuclei in the brains of vertebrates, situated at the base of the forebrain and strongly connected with the cerebral cortex, thalamus and pons. The basal ganglia are associated with a variety of functions, including arousal, motor control and learning. The main components of the basal ganglia are the striatum, pallidum, substantia nigra, and subthalamic nucleus
Subthalamic nucleus
The subthalamic nucleus is a small lens-shaped nucleus in the brain where it is, from a functional point of view, part of the basal ganglia system. Anatomically, it is the major part of subthalamus. As suggested by its name, the subthalamic nucleus is located ventral to the thalamus. It is also...
(or subthalamus). This latter, glutamatergic nucleus is reciprocally connected with the PGO-transferring nuclei of the pons
Pons
The pons is a structure located on the brain stem, named after the Latin word for "bridge" or the 16th-century Italian anatomist and surgeon Costanzo Varolio . It is superior to the medulla oblongata, inferior to the midbrain, and ventral to the cerebellum. In humans and other bipeds this means it...
. In humans, subthalamic PGO-like waves, that resemble the PGO waves typically recorded in cats, can be recorded during pre-REM and REM sleep. This suggests that the subthalamus may play an active role in an ascending activating network implicated in the rostral transmission of PGO waves during REM sleep in humans.
PGO waves and REM sleep
PGO waves are an integral part of rapid eye movement (REM) sleep. As stated earlier, the density of the PGO waves coincides with the amount of eye movement measured in REM sleep. This has led some researchers to further theorize about the usefulness of PGO waves for dreaming.One key use of REM sleep is for the brain to process and store information from the previous day. In a sense, the brain is learning by establishing new neuronal connections for things that have been learned. Neurophysiological studies have indicated a relationship between increased P-wave density during post-training REM sleep and learning performance. Basically, the abundance of PGO waves translates into longer periods of REM sleep, which thereby allows the brain to have longer periods where neuronal connections are formed.
The importance of PGO waves during REM sleep also aids the idea of PGO waves being a signal that a person is dreaming. Since dreaming occurs during REM sleep, the PGO waves are theorized to be the signals that make the brain start to recount the experiences from the previous day. This, in turn, allows us to "see" our dreams since our visual sense is quickly going through the information it has stored.
For more information of the importance of PGO waves during REM sleep, please refer to Activation synthesis theory.
Future research
While there is a good, basic understanding of PGO waves with a lot of theories, there is still a lot we have yet to learn about the function of these neuroelectric signals.The next big area to research regarding this topic is to understand what processes PGO waves are beneficial for in both states of sleep as well as consciousness. Although PGO waves are noticeably present during NREM sleep, some scientists believe they are also present during waking cycles. There is a possibility that PGO waves are essential for image correction of the eyes, since PGO waves are signals on a pathway that allow the motor cortex of the brain to interface with the vision system.
The other future interests in research of this topic are what PGO waves are precisely doing for us while we are dreaming. Some scientists theorize that PGO waves are essential for stabilizing the images that we have in our dreams. This theory comes from the eye movements that coincide with the readings from electrodes picking up PGO waves.
Also, scientists seek to discover how the presence of these signals fits in with the overall dreaming process. Current trends in neurophysiology tend to focus on cell to cell connections of neurons, but many know that we still need to research the bigger picture ideas of this field of research. The importance of PGO waves is one of those broad approaches to neurophysiology because it involves the coordination of entire regions of the brain to work together—coming from many different systems—to create our dreams, memories, and other experiences that we have.
Another area of research interest would be to look at PGO waves during lucid dreaming, since the brain is both asleep and awake at the very same time.
Additional images
See also
- DreamDreamDreams are successions of images, ideas, emotions, and sensations that occur involuntarily in the mind during certain stages of sleep. The content and purpose of dreams are not definitively understood, though they have been a topic of scientific speculation, philosophical intrigue and religious...
- ElectroencephalographyElectroencephalographyElectroencephalography 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) - SleepSleepSleep is a naturally recurring state characterized by reduced or absent consciousness, relatively suspended sensory activity, and inactivity of nearly all voluntary muscles. It is distinguished from quiet wakefulness by a decreased ability to react to stimuli, and is more easily reversible than...
- REM sleep
- NREM sleep
- PonsPonsThe pons is a structure located on the brain stem, named after the Latin word for "bridge" or the 16th-century Italian anatomist and surgeon Costanzo Varolio . It is superior to the medulla oblongata, inferior to the midbrain, and ventral to the cerebellum. In humans and other bipeds this means it...
- Lateral geniculate nucleusLateral geniculate nucleusThe lateral geniculate nucleus is the primary relay center for visual information received from the retina of the eye. The LGN is found inside the thalamus of the brain....
- Occipital LobeOccipital lobeThe occipital lobe is the visual processing center of the mammalian brain containing most of the anatomical region of the visual cortex. The primary visual cortex is Brodmann area 17, commonly called V1...
- Subthalamic nucleusSubthalamic nucleusThe subthalamic nucleus is a small lens-shaped nucleus in the brain where it is, from a functional point of view, part of the basal ganglia system. Anatomically, it is the major part of subthalamus. As suggested by its name, the subthalamic nucleus is located ventral to the thalamus. It is also...
- Alpha waveAlpha 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...
- Beta waveBeta waveBeta 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...
- Delta waveDelta waveA 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...
- Gamma waveGamma waveA 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...
- Mu waveMu waveMu 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...
- Theta wave