Pho-meet up2

Eman youssif

Neural oscillations are observed throughout the central nervous system and at all levels, e.g., spike trains, local field

potentials and large-scale oscillations which can be measured by electroencephalography. In general,

oscillations can be characterized by their frequency, amplitude and phase. These signal properties can be

extracted from neural recordings using time-frequency analysis. In large-scale oscillations, amplitude changes are

considered to result from changes in synchronization within a neural ensemble, also referred to as local synchronization.

In addition to local synchronization, oscillatory activity of distant neural structures (single neurons or neural

ensembles) can synchronize. Neural oscillations and synchronization have been linked to many cognitive

functions such as information transfer, perception, motor control and memory

Although neural oscillations in human brain activity are mostly investigated using EEG recordings, they are also observed using

more invasive recording techniques such as single-unit recordings. Neurons can generate rhythmic patterns of action

potentials or spikes. Some types of neurons have the tendency to fire at particular frequencies, so-called resonators.[8] Bursting

is another form of rhythmic spiking. Spiking patterns are considered fundamental for information coding in the brain.

Oscillatory activity can also be observed in the form of subthreshold membrane potential oscillations (i.e. in the

absence of action potentials).[9] If numerous neurons spike in synchrony, they can give rise to oscillations in local field

potentials (LFPs). Quantitative models can estimate the strength of neural oscillations in recorded data

The functions of neural oscillations are wide ranging and vary for different types of oscillatory activity. Examples are the generation of rhythmic activity such as a heartbeat and the neural binding of sensory features in perception, such as the shape and color of an object. Neural oscillations also play an important role in many neurological disorders, such as excessive synchronization during seizure activity in epilepsy or tremor in patients with Parkinson's disease. Oscillatory activity can also be used to control external devices in brain-computer interfaces, in which subjects can control an external device by changing the amplitude of particular brain rhythmics.

Oscillatory activity is observed throughout the central nervous system at all levels of organization. Three different levels have been widely recognized: the micro-scale (activity of a single neuron), the meso-scale (activity of a local group of neurons) and the macro-scale (activity of different brain regions).

Neurons generate action potentials resulting from changes in the electric membrane potential. Neurons can generate multiple action potentials in sequence forming so-called spike trains. These spike trains are the basis for neural coding and information transfer in the brain. Spike trains can form all kinds of patterns, such as rhythmic spiking and bursting, and often display oscillatory activityMicroscopic(

Mesoscopic:A group of neurons can also generate oscillatory activity. Through synaptic

interactions the firing patterns of different neurons may become synchronized and the rhythmic changes in electric potential caused by their

action potentials will add up (constructive interference). That is, synchronized firing patterns result in synchronised input into other cortical areas, which gives rise to large-amplitude oscillations of the local field potential. These

large-scale oscillations can also be measured outside the scalp using electroencephalography (EEG) and magnetoencephalography (MEG) .

Macroscopic:Neural oscillation can also arise from interactions between

different brain areas. Time delays play an important role here. Because all brain areas are bidirectionally coupled, these

connections between brain areas form feedback loops. Positive feedback loops tends to cause oscillatory activity which

frequency is inversely related to the delay time. An example of such a feedback loop is the connections between the thalamus

and cortex. This thalamocortical network is able to generate oscillatory activity known as recurrent thalamo-cortical

resonance.[16] The thalamocortical network plays an important role in the generation of alpha activity

IMPORTANT:Neural synchronization can be modulated by task

constraints, such as attention, and is thought to play a role in feature binding,[49] neuronal communication,[1] and motor

coordination.[3] Neuronal oscillations became a hot topic in neuroscience in the 1990s when the studies of the visual system of the

brain by Gray, Singer and others appeared to support the neural binding hypothesis.[50] According to this idea, synchronous

oscillations in neuronal ensembles bind neurons representing different features of an object. For example, when a person looks at a tree,

visual cortex neurons representing the tree trunk and those representing the branches of the same tree would oscillate in

synchrony to form a single representation of the tree. This phenomenon is best seen in local field potentials which reflect the synchronous activity of local groups of neurons, but has also been

shown in EEG and MEG recordings providing increasing evidence for a close relation between synchronous oscillatory activity and a variety of

cognitive functions such as perceptual grouping

Neural oscillations are extensively linked to memory function, in particular theta activity. Theta rhythms are very strong in rodent hippocampi and

entorhinal cortex during learning and memory retrieval, and are believed to be vital to the induction of long-term potentiation, a potential cellular

mechanism of learning and memory. The coupling between theta and gamma activity is thought to be vital for memory functions, including episodic

memory.[73][74] The tight coordination of spike timing of single neurons with the local theta oscillations is linked to successful memory formation in

humans, as more stereotyped spiking predicts better memory

Alpha wave

Alpha waves are neural oscillations in the frequency range of 8–13 Hz arising from synchronous and coherent (in phase or

constructive) electrical activity of thalamic pacemaker cells in humans. They are also called Berger's wave in memory of the founder of EEG.

Alpha waves are one type of brain waves detected either by electroencephalography (EEG) or magnetoencephalography (MEG) and predominantly originate from the occipital lobe

during wakeful relaxation with closed eyes.

The second occurrence of alpha wave activity is during REM sleep. As opposed to the awake form of alpha activity, this form

is located in a frontal-central location in the brain

Alpha wave intrusion occurs when alpha waves appear with non-REM sleep when delta activity is expected. It is hypothesized to be associated with fibromyalgia,[9] although the study may be inadequate due to a small

sampling size.

Despite this, alpha wave intrusion has not been significantly linked to any major sleep disorder, including fibromyalgia, chronic fatigue syndrome, and major depression. However, it is common in chronic fatigued patients, and

may amplify the effects of other sleep disorders

Binaural beats may influence functions of the brain in ways besides those related to hearing. This phenomenon is called "frequency following

response". The concept is that if one receives a stimulus with a frequency in the range of brain waves, the predominant brainwave frequency is said to be

likely to move towards the frequency of the stimulus (a process called entrainment).[20] In addition, binaural beats have been credibly documented

to relate to both spatial perception and stereo auditory recognition, and, according to the frequency following response, activation of various sites in

the brain

Perceived human hearing is limited to the range of frequencies from 20 Hz to 20,000 Hz, but the frequencies of human brain waves are below about

40 Hz. To account for this lack of perception, binaural beat frequencies

are used. Beat frequencies of 40 Hz have been produced in the brain with

binaural sound and measured experimentally

When the perceived beat frequency corresponds to the delta, theta, alpha, beta, or gamma range of brainwave frequencies, the brainwaves entrain to or move towards the beat frequency.[29] For example, if a 315 Hz sine wave is played into the right ear and a 325 Hz one into the left ear, the brain is entrained towards the beat frequency 10 Hz, in the alpha range. Since alpha range is associated with relaxation, this has a relaxing effect, or if in the theta range, more alertness. An experiment with binaural sound stimulation using beat frequencies in the beta range on some participants and the delta/theta range on other participants found better vigilance performance and mood in those on the awake alert state of beta-range stimulation

Binaural beat stimulation has been used fairly extensively in attempts to induce a variety of states of consciousness, and there has been some work done in regards to the effects of these stimuli on relaxation, focus, attention, and states of consciousness.[8] Studies have shown that with repeated

training to distinguish close frequency sounds that a plastic reorganization of the brain occurs for the trained frequencies[32]

and is capable of asymmetric hemispheric balancing

Alpha-theta brainwave training has also been used successfully for the

treatment of addictions

An uncontrolled pilot study of delta binaural beat technology over 60 days has shown positive effects on self-reported

psychologic measures, especially anxiety. There was a significant decrease in trait anxiety, an increase in quality of life, and a

decrease in insulin-like growth factor-1 and dopamine,[1] and it has been successfully shown to decrease mild anxiety.[41] A

randomised, controlled study concluded that binaural beat audio could lessen hospital acute pre-operative anxiety

Another claimed effect for sound-induced brain synchronization is enhanced learning ability. It was proposed in the 1970s that

induced alpha brain waves enabled students to assimilate more information with greater long-term retention.[43] In more recent

times has come more understanding of the role of theta brain waves in behavioural learning.[44] The presence of theta patterns in the brain has been associated with increased receptivity for learning and decreased filtering by the left

hemisphere.[43][45][46] Based on the association between theta activity (4–7 Hz) and working memory performance, biofeedback

training suggests that normal healthy individuals can learn to increase a specific component of their EEG activity, and that such enhanced activity may facilitate a working memory task and to a

lesser extent focused attention

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[1] (EEG) and are

usually associated with the deepest stages of sleep (3 NREM), also known as slow-wave sleep

(SWS), and aid in characterizing the depth of sleep

Females have been shown to have more delta wave activity, and this is true across most mammal species. This discrepancy does

not become 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.

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 formation

Delta activity stimulates the release of several hormones, including growth hormone releasing hormone GHRH and

prolactin (PRL). GHRH is released from the hypothalamus, 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

Theta rhythm

Cortical theta rhythms" are low-frequency components of scalp EEG, usually recorded from

humans.In human EEG studies, the term theta refers to

frequency components in the 4–7 Hz range, regardless of their source. Cortical theta is observed frequently in young children. In older children and adults, it tends to appear during meditative, drowsy, or sleeping states, but not during the deepest stages of sleep. Several

types of brain pathology can give rise to abnormally strong or persistent cortical theta waves.

mu waveMu waves, also known as mu rhythms, comb or

wicket rhythms, arciform rhythms, or sensorimotor rhythms, are synchronized patterns of electrical

activity involving large numbers of neurons, probably of the pyramidal type, in the part of the brain that controls voluntary movement.[1] These patterns as

measured by electroencephalography (EEG), magnetoencephalography (MEG), or

electrocorticography (ECoG) repeat at a frequency of 8–13 Hz and are most prominent when the body is

physically at rest

The right fusiform gyrus, left inferior parietal lobule, right anterior parietal cortex, and left inferior frontal gyrus are of

particular interest.[7][11][12] Some researchers believe that mu wave suppression can be a consequence of mirror neuron

activity throughout the brain, and represents a higher-level integrative processing of mirror neuron activity.[3] Tests in both

monkeys (using invasive measuring techniques) and humans (using EEG and fMRI) have found that these mirror neurons not

only fire during basic motor tasks, but also have components that deal with intention.[13] There is evidence of an important

role for mirror neurons in humans, and mu waves may represent a high level coordination of those mirror neurons

Mu waves are thought to be indicative of an infant’s developing ability to imitate. This is important because

the ability to imitate plays a vital role in the development of motor skills, tool use, and

understanding causal information through social interaction

recording of electrical activity over the motor cortex.

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 (12

to 30 transitions or cycles per second). Beta waves are split into three sections: Low Beta Waves (12.5-16 Hz, "Beta 1 power"); Beta Waves (16.5–20 Hz, "Beta 2 power"); and High Beta Waves (20.5-28 Hz, "Beta 3 power").[1] Beta states are the states associated

with normal waking consciousness.

Low amplitude beta waves with multiple and varying frequencies are often associated with active, busy, or anxious thinking and active concentration.[2]

Over the motor cortex beta waves are associated with the muscle contractions that happen in isotonic movements and are suppressed prior to and during movement changes.[3] Bursts of beta activity are associated with a strengthening of sensory

feedback in static motor control and reduced when there is movement change.[4] Beta activity is increased when movement has to be resisted or voluntarily suppressed.[5]

The artificial induction of increased beta waves over the motor cortex by a form of electrical stimulation called Transcranial alternating-current stimulation consistent

with its link to isotonic contraction produces a slowing of motor movements

Gamma wave

A gamma wave is a pattern of neural oscillation in humans with a frequency between 25 and 100

Hz,[1] though 40 Hz is typical.[2]

According to a popular theory, gamma waves may be implicated in creating the unity of

conscious perception (the binding problem)

Role in attentive focushe proposed answer lies in a wave that, originating in the thalamus, sweeps

the brain from front to back, 40 times per second, drawing different neuronal circuits into synch with the precept, and thereby bringing the precept into the attentional foreground. If the thalamus is damaged even a little bit, this wave stops, conscious awarenesses do not form, and the patient slips into profound

coma.

Thus the claim is that when all these neuronal clusters oscillate together during these transient periods of synchronized firing, they help bring up memories and associations from the visual precept to other notions. This brings a distributed matrix of

cognitive processes together to generate a coherent, concerted cognitive act, such as perception. This has led to theories that gamma waves are associated with solving the binding problem

Delta wave – (0.1–4 Hz)Theta wave – (4–8 Hz)Mu wave – (8–13 Hz)

Beta wave – (13–30 Hz)Gamma wave – (25–100 Hz)