High-frequency oscillations (HFO) are

brain wave ''Brain Wave'' is a science fiction novel by American writer Poul Anderson, first published in serial form in ''Space Science Fiction'' in 1953, and then as a novel in 1954. Anderson had said that he could consider it one of his top five books. Th ...

s of the frequency faster than ~80 Hz, generated by

neuron A neuron, neurone, or nerve cell is an electrically excitable cell that communicates with other cells via specialized connections called synapses. The neuron is the main component of nervous tissue in all animals except sponges and placozoa. N ...

al cell population. High-frequency oscillations can be recorded during an

electroencephalagram Electroencephalography (EEG) 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 ...

(EEG),

local field potential Local field potentials (LFP) are transient electrical signals generated in nervous and other tissues by the summed and synchronous electrical activity of the individual cells (e.g. neurons) in that tissue. LFP are "extracellular" signals, meaning ...

(LFP) or electrocorticogram (ECoG)

electrophysiology Electrophysiology (from Greek , ''ēlektron'', "amber" etymology of "electron"">Electron#Etymology">etymology of "electron" , ''physis'', "nature, origin"; and , '' -logia'') is the branch of physiology that studies the electrical properties of b ...

recordings. They are present in physiological state during sharp waves and ripples - oscillatory patterns involved in

memory consolidation Memory consolidation is a category of processes that stabilize a memory trace after its initial acquisition. A memory trace is a change in the nervous system caused by memorizing something. Consolidation is distinguished into two specific processe ...

processes. HFOs are associated with pathophysiology of the brain like epileptic seizure and are often recorded during seizure onset. It makes a promising biomarker for the identification of the epileptogenic zone. Other studies points to the HFO role in

psychiatric disorders A mental disorder, also referred to as a mental illness or psychiatric disorder, is a behavioral or mental pattern that causes significant distress or impairment of personal functioning. Such features may be persistent, relapsing and remitti ...

and possible implications to psychotic episodes in

schizophrenia Schizophrenia is a mental disorder characterized by continuous or relapsing episodes of psychosis. Major symptoms include hallucinations (typically hearing voices), delusions, and disorganized thinking. Other symptoms include social withdra ...

Background and history

Traditional classification of the frequency bands, that are associated to different functions/states of the brain and consist of

delta Delta commonly refers to: * Delta (letter) (Δ or δ), a letter of the Greek alphabet * River delta, at a river mouth * D (NATO phonetic alphabet: "Delta") * Delta Air Lines, US * Delta variant of SARS-CoV-2 that causes COVID-19 Delta may also re ...

theta Theta (, ; uppercase: Θ or ; lowercase: θ or ; grc, ''thē̂ta'' ; Modern: ''thī́ta'' ) is the eighth letter of the Greek alphabet, derived from the Phoenician letter Teth . In the system of Greek numerals, it has a value of 9. Gr ...

alpha Alpha (uppercase , lowercase ; grc, ἄλφα, ''álpha'', or ell, άλφα, álfa) is the first letter of the Greek alphabet. In the system of Greek numerals, it has a value of one. Alpha is derived from the Phoenician letter aleph , whic ...

beta Beta (, ; uppercase , lowercase , or cursive ; grc, βῆτα, bē̂ta or ell, βήτα, víta) is the second letter of the Greek alphabet. In the system of Greek numerals, it has a value of 2. In Modern Greek, it represents the voiced labiod ...

and

gamma Gamma (uppercase , lowercase ; ''gámma'') is the third letter of the Greek alphabet. In the system of Greek numerals it has a value of 3. In Ancient Greek, the letter gamma represented a voiced velar stop . In Modern Greek, this letter re ...

bands. Due to the limited capabilities of the early experimental/medical setup to record fast frequencies, for historical reason, all oscillations above 30 Hz were considered as high frequency and were difficult to investigate. Recent advance in manufacturing electrophysiological setups enables to record

electric potential The electric potential (also called the ''electric field potential'', potential drop, the electrostatic potential) is defined as the amount of work energy needed to move a unit of electric charge from a reference point to the specific point in ...

with high temporal and space resolution, and to "catch" dynamics of single cell

action potential An action potential occurs when the membrane potential of a specific cell location rapidly rises and falls. This depolarization then causes adjacent locations to similarly depolarize. Action potentials occur in several types of animal cells, ...

. In neuroscience nomenclature, there is still a reaming gap between ~100 Hz and

multi unit activity Multi is a shortened form of "multiple". It may refer to: * Alternate character, in online gaming * Multi two diamonds, a contract bridge convention * Multirhyme, a synonym for feminine rhyme used in hip hop music * Multi (''To Heart''), a charac ...

(>500 Hz), so these oscillations are often called high gamma or HFO.

Neurophysiological features

HFO are generated by different cellular mechanisms and can be detected in many brain areas. In

hippocampus The hippocampus (via Latin from Greek , 'seahorse') is a major component of the brain of humans and other vertebrates. Humans and other mammals have two hippocampi, one in each side of the brain. The hippocampus is part of the limbic system, a ...

, this fast neuronal activity is effect of the population synchronous spiking of pyramidal cells in the CA3 region and

dendritic Dendrite derives from the Greek word "dendron" meaning ( "tree-like"), and may refer to: Biology *Dendrite, a branched projection of a neuron *Dendrite (non-neuronal), branching projections of certain skin cells and immune cells Physical * Dendr ...

layer of the CA1, which give rise to a characteristic oscillation pattern (see more in sharp waves and ripples). The HFO occurrence during memory task (encoding and recalling images) was also reported in human patients from intracranial recordings in primary visual,

limbic The limbic system, also known as the paleomammalian cortex, is a set of brain structures located on both sides of the thalamus, immediately beneath the medial temporal lobe of the cerebrum primarily in the forebrain.Schacter, Daniel L. 2012. ''Ps ...

and higher order cortical areas. Another example of physiological HFO of around 300 Hz, was found in

subthalamic nucleus The subthalamic nucleus (STN) is a small lens-shaped nucleus in the brain where it is, from a functional point of view, part of the basal ganglia system. In terms of anatomy, it is the major part of the subthalamus. As suggested by its name, the ...

, the brain region which is the main target for high-frequency (130 Hz) deep brain stimulation treatment for patients with

Parkinson's disease Parkinson's disease (PD), or simply Parkinson's, is a long-term degenerative disorder of the central nervous system that mainly affects the motor system. The symptoms usually emerge slowly, and as the disease worsens, non-motor symptoms becom ...

Somatosensory evoked high-frequency oscillations

ECoG recordings from human somatosensory cortex, has shown HFO (reaching even 600 Hz) presence during sensory evoked potentials and somatosensory evoked magnetic field after

median nerve The median nerve is a nerve in humans and other animals in the upper limb. It is one of the five main nerves originating from the brachial plexus. The median nerve originates from the lateral and medial cords of the brachial plexus, and has contr ...

stimulation. These bursts of activity are generated by thalamocortical loop and driven by highly synchronized spiking of the thalamocortical fibres, and are thought to play a role in information processing. Somatosensory evoked HFO amplitude changes may be potentially used as biomarker for neurologic disorders, which can help in diagnosis in certain clinical contexts. Some oncology patients with

brain tumor A brain tumor occurs when abnormal cells form within the brain. There are two main types of tumors: malignant tumors and benign (non-cancerous) tumors. These can be further classified as primary tumors, which start within the brain, and seconda ...

s showed higher HFOs amplitude on the same side, where the tumor was. Authors of this study also suggest contribution from the thalamocortical pathways to the fast oscillations. Interestingly, higher HFO amplitudes (between 400 and 800 Hz) after nerve stimulation were also reported in the EEG signal of healthy

football Football is a family of team sports that involve, to varying degrees, kicking a ball to score a goal. Unqualified, the word ''football'' normally means the form of football that is the most popular where the word is used. Sports commonly c ...

and

racquet sports Racket sports are games in which players use a racket or paddle to hit a ball or other object. Rackets consist of a handled frame with an open hoop that supports a network of tightly stretched strings. Paddles have a solid face rather than a ne ...

players.

Pathological HFO

There are many studies, that reports pathophysiological types of HFO in human patients and animal models of disease, which are related to different psychiatric or neurological disorders: * Amplitude aberrations of the sensory evoked HFOs (600 Hz) was reported in mild demyelination in

multiple sclerosis Multiple (cerebral) sclerosis (MS), also known as encephalomyelitis disseminata or disseminated sclerosis, is the most common demyelinating disease, in which the insulating covers of nerve cells in the brain and spinal cord are damaged. This d ...

patients. * HFO (>80 Hz) occur during epileptic seizure onset. * Disruption in the HFO (200–500 Hz) synchronization in

is related to

symptoms. * HFOs are visible in different brain regions just after cardiac-arrest and are linked to near-death states. * High amplitude HFOs (80–200 Hz) bursts correlates with psychotic-like state evoked with PCP or subanesthetic dose of

ketamine Ketamine is a dissociative anesthetic used medically for induction and maintenance of anesthesia. It is also used as a recreational drug. It is one of the safest anesthetics, as, in contrast with opiates, ether, and propofol, it suppresses ne ...

(and other

NMDA receptor The ''N''-methyl-D-aspartate receptor (also known as the NMDA receptor or NMDAR), is a glutamate receptor and ion channel found in neurons. The NMDA receptor is one of three types of ionotropic glutamate receptors, the other two being AMPA rece ...

blockers).

NMDA receptor hypofunction HFO

There are increasing number of studies indicating that HFO rhythms (130–180 Hz) may arise due to the local NMDA receptor blockage, which is also a pharmacological model of schizophrenia. These NMDA receptor dependent fast oscillations were detected in different brain areas including

nucleus accumbens The nucleus accumbens (NAc or NAcc; also known as the accumbens nucleus, or formerly as the ''nucleus accumbens septi'', Latin for "nucleus adjacent to the septum") is a region in the basal forebrain rostral to the preoptic area of the hypotha ...

and

prefrontal cortex In mammalian brain anatomy, the prefrontal cortex (PFC) covers the front part of the frontal lobe of the cerebral cortex. The PFC contains the Brodmann areas BA8, BA9, BA10, BA11, BA12, BA13, BA14, BA24, BA25, BA32, BA44, BA45, BA46, ...

regions. Despite the fact, that these type of HFO was not yet confirmed in human patients, second generation antipsychotic drugs, widely used to treat schizophrenia and schizoaffective disorders (i.e. Clozapine, Risperidone), was shown to reduce HFO frequency. Recent studies, reports on the new source of HFO in the olfactory bulb structures, which is surprisingly stronger than any other previously seen in the mammalian brain. HFO in the bulb is generated by local excitatory-inhibitory circuits modulated by breathing rhythm and may be also recorded under ketamine-xylazine anesthesia. This findings may aid understanding early symptoms of schizophrenia patients and their relatives, that can suffer from olfactory system impairments.

References

{{EEG Neuroscience Neural coding Neural circuits Neurophysiology Electrophysiology Computational neuroscience