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<h3><i style="font-size: 1rem;">“Ever since electrical activity has been recorded in the brain without evidence of an inducing external agent, it has been referred to as “spontaneous” (Buszaki, p. 12). “Complex systems, such as the brain, live by the rules of non-linear dynamics, better known as chaos theory” Buszaki, (p. 13).</i></h3>
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<p>Theories of how EEG arises and propagates itself are still evolving. The EEG at the surface of the cortex reflects the summated activity of ensembles of cells in the form of extracellular current flow. This summated activity is due apparently to synchronously
    activated postsynaptic potentials from vertically oriented pyramidal cells. Thus, the production of Local Field Potentials (LFPs) is what is picked up by the electroencephalograh (i.e. amplifier), and LFPs are observed only as radially-oriented (i.e.
    right-angle) dendrites excitatory action potentials summate in the cortical gyri and sulci. That means that the deeper pyramidal neurons do not affect the EEG to as large an extent (although they still affect the data). The further the distance from
    the scalp, the less the voltage of the action potentials.</p>
<p>Here is a short video of action potentials:&nbsp;<a href="https://www.youtube.com/watch?v=W2hHt_PXe5o">Action Potentials</a></p>
<p><a name="_Toc29328756" style="color: rgb(55, 71, 79); font-family: &quot;Open Sans&quot;; font-size: 1.715rem; background-color: rgb(255, 255, 255);">Action potential occurring along an axon</a></p>
<p style="text-align: center;"><span style="font-size: 1rem;">&nbsp;</span><img src="@@PLUGINFILE@@/Action%20Potentials.png" alt="Action potentials" width="533" height="347" style="font-size: 1rem;"></p>
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<p><span>What we see in the EEG is limited to measuring what is occurring at the cortical excitatory pyramidal neurons, which make up about 80% of the human cortex (or 80 billion of the 100 billion). The high density clustering these excitatory pyramidal neurons’ synapses create high density network nodes, or hubs in the brain, which serve as metaphorical substations for the relay of energy across functional networks in the brain (Hagmann et al., 2008; He et al., 2008). The actions of inhibitory neurons is not visible in the EEG, however, inhibitory neurons serve to hyperpolarize action potentials of pyramidal neurons into in-phase and anti-phase dynamics. And balancing of opposing forces, such as excitation and inhibition, often gives rise to rhythmic behavior. The mean time difference between&nbsp; the discharges of any two pairs of cells is zero; that is, interneurons discharge synchronously at approximately the same time. And neurons in&nbsp;&nbsp;the inhibitory network will be inhibited at the same time and fire simultaneously after inhibition wears off. Discharge and silence will alternate in all parts of the network synchronously (Buszaki, p. 75). On average, all neurons will fire at zero lag time and will be silenced at the same time (p. 76). Oscillator networks made from homogenous inhibitory neurons can have a large deteriorating effect on subsequent synchronous discharge of the&nbsp;<a name="_Hlk16500290">neurons. This may explain why gamma-frequency oscillations are typically short-lasting, transient events (Buszaki, p. 76)</a></span></p>
<p>GABAergic inhibitory neurons can aid to synchronize neurons in a coordinated manner (into cross-frequency phase shift and phase lock) by shifting the membrane potentials of pyramidal neurons.</p><br>
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<h3><a name="_Toc29328757">Pyramidal Neurons</a></h3>
<p style="text-align: center;"><img src="@@PLUGINFILE@@/Pyramidal%20Neurons.png" alt="Pyramidal Neurons" width="500" height="281" style="font-size: 1rem;" class="atto_image_button_text-bottom"></p>
<p>According to Duffy (1989), excitatory neurotransmitters evoke an electrical change in the excitatory postsynaptic membrane potentials (EPSP), depolarizing the post synaptic membrane and leading eventually to an action potential, while inhibitory neurotransmitters
    result in increased negative charge inside the cell membrane known as the inhibitory postsynaptic potential (IPSP) that hyperpolarizes the cell membrane and inhibits depolarization. Excitatory post synaptic potentials move positive ions (sodium, calcium
    and potassium) down axons and inhibitory post synaptic potentials move negative ions (chlorine) down axons. When recording an EEG, 50% of the data arriving at the site of the electrode is from neurons directly underneath it, and 95% of the data comes
    from within 6 centimeters distance (that’s a circle with a diameter of 2&nbsp;<sup>1/3</sup>&nbsp;inches—big).</p>
<p>Here is a video of a neuron firing:&nbsp;<a href="https://www.youtube.com/watch?v=WhowH0kb7n0&amp;t=44s">Synaptic Transmission</a></p>
<p>There are two types of connections between synapses: <b>electrical and chemical</b> synapses. Electrical synapses produce very short and high-speed communication (200 nsec to a few msec), which are too short to be measured at the scalp surface, due to
    filtering properties of the skull. However, chemical synapses, which are responsible for the swap of neurotransmitters (small molecules) and neuromodulators (large molecules), produce short duration electrical potentials of 100msec to seconds, which
    are readable via EEG (1 to 300Hz with intra-cerebral electrodes and 1 – 50Hz with scalp electrodes) (Buzsaki, 2006).&nbsp;&nbsp;</p><p>There are “fast synapses” and “slow synapses”. Fast synapses encompass 90% of excitatory synapses, which are modulated with
    the neurotransmitter glutamate, and 90% of inhibitory synapses, which are modulated by the neurotransmitter GABA. Slow synapses encompass the other 20% are long duration synaptic potentials that last for 100 msec to 1 sec and are modulated by dopamine,
    acetycholine, serotonin, norepinephrine and histamine (these molecules are within a sub-class of neurotransmitters, called neuromodulators, due to the lack of re-uptake mechanism) (Thatcher, 2012). Fast synapses&nbsp; oscillate at 0 – 80msec and slow
    synapses oscillate at 100 msec – 1 second), thus the frequencies of 0-80 msec (12.5+ Hz) are ruled by the gaba/glutamate allostasis and the frequencies of 10Hz (100 msec to 1 sec) and under are ruled by the slow synaptic neuromodulators. The frequencies
    of 10 – 12.5Hz are a blend of fast and slow synapses. If you brain is not producing noephinephrine, your alpha is likely too slow and if you have too much GABA, your alpha is likely too fast.</p><p><br></p>
<h2><a name="_Toc29328758">Slow Cortical Potentials and Infraslow Frequencies</a></h2><br>
<p></p>
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<p><p>Infraslow Frequencies (ISF) and Slow Cortical Potentials
(SCP) are negative or positive polarizations of the EEG. ISFs are 0.01Hz to
0.1Hz. &nbsp;Slow cortical potentials are
0.1Hz to 1Hz.Both ISFs and SCPs reflect the depolarization of large cortical
cell assemblies (seen in the apical dendrites of large groups of pyramidal
neurons) reducing their excitation threshold. Sheets of cortical neurons
depolarize in the creation of ISF/SCPs, creating electro-negative swings.
They are described as a phasic tuning mechanism related to activities in the
brain stem reticular process, the thalamus and the basal ganglia.<span style="font-size: 1rem;">&nbsp;Slow cortical
    potentials and infraslow frequencies bind networks (this is the binding frequency of consciousness, not gamma—gamma is the by-product of being bound).</span></p><p><span style="font-size: 1rem;"><p>ISF/SCPs bind resting state networks (RSN) (also called intrinsic
connectivity networks). They have to do with hemodynamics, the burning of blood
glucose (this is where blood sugar is metabolized), and resting state potential
dynamics.&nbsp;<em><b>Glucose</b></em>&nbsp;comes from the Greek word for "sweet." When you metabolize blood sugar (glucose), you create the by-product of bi-carbonate ions (a form of carbon dioxide, also known as HCO3) in the blood, which generates an electro-negative charge. Your blood brings bicarbonate to your lungs, and then it is exhaled as carbon dioxide. Your kidneys also help regulate bicarbonate. Bicarbonate is excreted and reabsorbed by your kidneys. This regulates your body's pH, or acid balance. Bicarbonate also works with sodium, potassium, and chloride, also called electrolytes. These are usually measured at the same time as bicarbonate.&nbsp;</p><p>Glial cells generate direct current and slow cortical potentials. In the human brain, these spontaneous
fluctuations are salient in blood oxygenation level-dependent (BOLD) signals,
reflecting underlying resting state network (RSN) dynamics. You have between 10-100 glia for every neuron.&nbsp;Glia have many roles, as will be covered later in this chapter. But, suffice it to say, glia are foremost know in acting like scaffolding for each neuron. There are shared hemodynamic and anatomical
connections in resting state networks (<a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6608153/#B30" rid="B30" role="button" aria-expanded="false" aria-haspopup="true">Leistner et al.,
2007</a>,&nbsp;<a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6608153/#B31" rid="B31" role="button" aria-expanded="false" aria-haspopup="true">2010</a>;&nbsp;<a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6608153/#B26" rid="B26" role="button" aria-expanded="false" aria-haspopup="true">Khader et al.,
2008</a>, <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6608153/#B21">He et al., 2008</a>;&nbsp;<a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6608153/#B22" rid="B22" role="button" aria-expanded="false" aria-haspopup="true">Helps et al.,
2010</a>;&nbsp;<a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6608153/#B12" rid="B12" role="button" aria-expanded="false" aria-haspopup="true">Broyd et al.,
2011</a>). In other words, SCPs and ISFs are a direct
electrophysiological correlate of BOLD signals, seen in resting state networks. </p><p>Negative shifts represent
increased probability of firing while positive shifts represent decreased
probability or inhibition. Negative shifts are described as related to the
utilization of resources for attention, memory, and other related cognitive
mechanisms. To ground this in example: it has been hypothesized that in
autism spectrum cases, the threshold of depolarization is too high and in ADHD
cases, the threshold of depolarization is too low. In ISF/SCP neurofeedback training,
ADHD children are taught to increase the negativity of the SCP, while autistic
and seizure cases are taught to decrease the negativity of the SCP. Additionally,
in patients with seizure conditions, large negative potential shifts have been
observed moments before a seizure. </p></span></p></p><br>
<h3>Slow Cortical Potentials</h3>
<p style="text-align: center; "><img src="@@PLUGINFILE@@/SCP.png" alt="SCP" width="301" height="244" class="img-responsive atto_image_button_text-bottom"><br></p>
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<h2><a name="_Toc29328759">Delta (1-4 Hz)</a></h2>
<p>Delta is 1 - 4 Hz, or oscillations per second. Delta is generated by the hypothalamus (a region of the forebrain below the thalamus which coordinates both the autonomic nervous system and the activity of the pituitary, controlling body temperature, thirst, hunger, and other homeostatic systems, and involved in sleep and emotional activity). It is fundamental to the mesolimbic dopamine system in the brain). Delta is also generated in dipoles within sheets of cortical tissues.&nbsp;</p><p>Delta arises from unmyelinated white matter in early life, and in adult states of deep dreamless sleep, when pacemakers in thalamic and septo-hippocampal, hypothalamic, and brainstem locations create
    the slow pulsing carrier wave rhythms of the EEG by activating large groups of synchronous neurons at the same time. Early in life delta is created by the fundamental neuronal structures of the reptilian system and delta appears during the initial
    migration of neurons across the lobe of the brain, as they form the basic networks of the brain that make up the fundamental architecture from which everything else springs forth.&nbsp;</p><p>When the brain is damaged, delta can be generated in healing tissues and may show up focally. This is an image of focal (or localized) delta activity.</p><p><img src="@@PLUGINFILE@@/Focal%20Delta.png" alt="Focal Delta" width="930" height="796" class="img-responsive atto_image_button_left"><br></p><p>Delta
rhythm in the awake state in adult EEG is an abnormal finding and is typically associated with pathology. A record showing diffuse delta and theta activity (when drowsiness is ruled out) will typically indicate developmental issues, issues of dementia, or severe developmental trauma. Artifacts with very slow
potentials, such as rolling eye movement (see page 3), pulse, sweat, and respiration may produce
similar frequencies &lt;4 Hz, in EEG recordings.</p><p>This image is the QEEG of the abnormal focal delta findings at the left temporal lobe.</p>
<p><img src="@@PLUGINFILE@@/Focal%20Delta%202.png" alt="Focal Delta" width="711" height="447" class="img-responsive atto_image_button_left"><br></p><p><br></p><p><br></p><p><br></p><p><br></p><p><br></p><p><br></p><p><br></p><p><br></p><p><br></p>
<h2><a name="_Toc29328760"><br></a></h2><h2><a name="_Toc29328760"><br></a></h2><h2><a name="_Toc29328760"><br></a></h2><h2><a name="_Toc29328760"><br></a></h2><h2><a name="_Toc29328760"><br></a></h2><h2><a name="_Toc29328760"><br></a></h2><h2><a name="_Toc29328760"><br></a></h2><h2><a name="_Toc29328760"><br></a></h2><h2><a name="_Toc29328760"><br></a></h2><h2><a name="_Toc29328760"><br></a></h2><h2><br></h2><h2><a name="_Toc29328760">Theta (4-8 Hz)</a></h2>
<p>Theta rhythm is a normal finding during drowsiness in the adult EEG. Theta, may be seen at
the onset of sleep as the alpha rhythm slows with drowsiness. The state of mind typically dominated by theta is that of dayream, hypnogogia, or trance. If theta
frequencies are present in an alert, adult’s EEG they are usually considered to be an abnormal
finding.</p><p>Since all thalamo-cortical activity is considered alpha, much theta activity is truly slowed alpha activity (which is recognizable by its sinusoidal shape). The thalamus can gate as slow as 2Hz and as fast as 14 hz. However, theta is limbically generated
    in the septo-hippocampal circuit, as well as generated by the nucleus accumbens in the forebrain.&nbsp;</p><p>Limbically generated theta is thought of as frontal midline theta, since the limbic projections are spatially limited, cortically, at the frontal and
    central midline. However, if it is longer than one second it is not frontal midline theta, but more the theta that is attention deficit disorder theta.&nbsp; Similar to delta, theta can be generated cortically when brain tissues are injured--delta typifies a more sever head injury (e.g. Traumatic Brain Injury), and theta will represent a lesser injury (e.g. concussion).</p>
<p>The image below is of a woman who is drowsy, with eyes open, showing a combination of theta and alpha frequencies.&nbsp;</p><p><img src="@@PLUGINFILE@@/Slow%20Alpha.png" alt="Slow Alpha" width="1279" height="718" class="img-responsive atto_image_button_left"><br></p>
<h3></h3><h3><br></h3><h3><br></h3><h3><br></h3><h3><br></h3><h3><br></h3><h3><br></h3><h3><br></h3><h3><br></h3><h3><br></h3><p><br></p><h3>Nucleus Accumbens</h3><br><img src="@@PLUGINFILE@@/Nucleus%20Accumbens.jpg" alt="Nucleus Accumbens" width="400" height="300" class="img-responsive atto_image_button_left">
<p>The nucleus accumbens is a part of the reward network (it is considered a monopole because all of the dipoles in it add to zero—it is tightly hooked to the rostral anterior cingulate). The nucleus accumbens provides acetycholine to the temporal lobes
    via the diagonal band of broca, which creates a feedback loop involving the amygdala and the hippocampus complex. The parahippocampal cortex reflects the temporal lobe's monopoles of the hippocampus and amygdala. This feedback loop creates the theta
    rhythm ,which is occurring in the septo-hippocampal circuit. &nbsp;Acetylcholine&nbsp;causes muscles to contract, activates pain responses and regulates endocrine and REM sleep functions.&nbsp;<span style="font-size: 1rem;">In ADD/ADHD the brain is dopamine deficient.</span></p>
<p><i>Interesting fact:&nbsp;</i><i>The venom of a black widow spider acts by causing the release of acetylcholine. When a person is bitten by a black widow, their acetylcholine levels rise dramatically, leading to severe muscle contractions, spasms, paralysis, and even death.</i></p><p><span style="color: rgb(55, 71, 79); font-family: &quot;Open Sans&quot;; font-size: 1.286rem;"><br></span></p><p style="text-align: center;"><span style="color: rgb(55, 71, 79); font-family: &quot;Open Sans&quot;; font-size: 1.286rem;">The Movement of Glutamate and Dopamine through the Brain</span><br></p>
<p style="text-align: center;"><img src="@@PLUGINFILE@@/Glutamate%20and%20Dopamine.png" alt="Glutamate and Dopamine" width="395" height="366"></p><p style="text-align: center;"><br></p>
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<h2><a name="_Toc29328761"><h2><br></h2><br></a></h2><h2><a name="_Toc29328761">Alpha</a></h2>

<p>Alpha is a 8-12Hz rhythm that is seen most readily in eyes closed EEG recordings.&nbsp;Alpha is a sinusoidal-like rhythm that tends to change in amplitude during an EEG recording.&nbsp;The average voltage of the normal adult alpha rhythm is 50 microvolts. Normal individuals may
have alpha voltages as high as 100 microvolts or as low as 20 microvolts. In some cases, the
alpha rhythm is seen only for a second after eye closure. Although alpha is usually seen in the
occipital regions, it may appear in the posterior temporal and parasagittal electrodes as well. The
alpha rhythm is sometimes slightly higher voltage over the right hemisphere.&nbsp;</p><p>Alpha rhythm attenuates, or diminishes, with eye opening and/or during mental activity/such as
concentrating to answer questions. In most cases, the alpha rhythm attenuates whenever the eyes
are open (reactive alpha). Less commonly, the alpha rhythm attenuates, or blocks, for only a
second or two with eye opening, returning almost immediately even if the individual's eyes
remain open (persistent alpha). Both types of alpha reactivity are considered normal.<br></p><p>Alpha is a frequency generated by the gating of the thalamus (it is received at the cortex and is thus, “thalamo-cortical”). It has been thought that the reticular nucleus of the thalamus is the specific alpha generator. When the EEG goes electro-positive, the thalamus closes.&nbsp; As the idling rhythm of the brain, alpha orchestrates (regulates)
    cortical function. Alpha often acts as a carrier wave that allows the content of gamma to be processed. The wave morphology of alpha is usually typified by a sinusoidal wave, although it may be more sharp than rounded in a few people, especially children
    and young adults.&nbsp; Current belief (Niedermeyer, 1999a; Steriade, Gloor, Llinas, Lopes da Silva, &amp; Musulam, 1990) is that there are cortico-cortico and thalamo-cortical generators of alpha which interact with one another, although there is
    no validation of a synchronizing mechanism at a cortical level.&nbsp;</p><p><img src="@@PLUGINFILE@@/alpha%20activity.jpg" alt="ALpha Activity" width="834" height="983" class="img-responsive atto_image_button_left"><br></p><h2><a name="_Toc29328762"><br></a></h2><h2><a name="_Toc29328762"><br></a></h2><h2><a name="_Toc29328762"><br></a></h2><h2><a name="_Toc29328762"><br></a></h2><h2><a name="_Toc29328762"><br></a></h2><h2><a name="_Toc29328762"><br></a></h2><h2><a name="_Toc29328762"><br></a></h2><h2><a name="_Toc29328762"><br></a></h2><h2><a name="_Toc29328762"><br></a></h2><h2><a name="_Toc29328762"><br></a></h2><h2><a name="_Toc29328762"><br></a></h2><h2><a name="_Toc29328762"><br></a></h2><h2><a name="_Toc29328762"><br></a></h2><h2><a name="_Toc29328762"><br></a></h2><h2><a name="_Toc29328762"><br></a></h2><h2><a name="_Toc29328762"><br></a></h2><h2><a name="_Toc29328762"><br></a></h2><h2><a name="_Toc29328762"></a><h2><a name="_Toc29328762"></a><a name="_Toc29328762">Sensory Motor Rhythm - SMR (12-15 Hz)&nbsp;</a></h2></h2><h5>SMR is also called Beta 1, and is a rhythm that has many functions. It is an awake and focused frequency, faster than alpha, but slower than the faster beta frequencies. This rhythm has been found to have anti-epileptic properties and is a frequency often in relative deficit to theta (hence it is a good counterbalance to excessive theta in neurofeedback as well as neurostimulation). Futhermore, this is the frequency range in which sleep spindles occur (a stabilizing mechanism of sleep).&nbsp;</h5><h2><a name="_Toc29328762">Beta (12-30 Hz)</a></h2><p><a name="_Toc29328762">Beta is a cortico-cortical frequency, generated by the six layers of pyramidal neurons that create the cortex of the brain. Beta is responsible for local communication within groups of neurons. Beta arrives in many states and conditions, from the point of birth onward, however its predominant function is executive functioning and processing of information for decision making. It is thought to be the brain wave that is responsible for higher level thinking.<br></a></p>

<p>The term "beta rhythm" was first used to describe frequencies faster than alpha rhythm by Hans
Berger in 1930. Beta rhythm is usually low voltage (less than 30 microvolts) in adults. Often,
during the awake EEG, beta is present in the anterior head area, but may be obscured by muscle
artifact (EMG) and eye movement potentials from the frontal electrodes (see illustration). Beta
rhythm is a normal finding in the adult awake EEG and can sometimes be better seen when the
patient's eyes are open. Beta rhythm is sometimes intermixed with other EEG rhythms of higher
voltage, such as the alpha rhythm, giving the alpha rhythm a notched or spiky appearance. Beta
is enhanced by drowsiness and some medications, especially gabaergic drugs.</p><p>The image below is of normal, awake beta activity in an adult's EEG.</p><p><img src="@@PLUGINFILE@@/beta%20%281%29.png" alt="beta" width="1000" height="957" class="img-responsive atto_image_button_left"><br></p><h2><a name="_Toc29328763">Gamma</a></h2>

<p>Gamma, which is 40+ Hz, is an emergent property in the EEG and does not have a generator, like the other frequencies. Gamma can be generated everywhere in the brain. Gamma is a resonant property of networks being bound, it arrives like a rainbow arrives
    via the combination of sun and water vapor. Gamma shows after receiving a stimulus and is thought to be the “aha!” or the moment of "Eureka!" of EEG. The below image is of a persistent frontal gamma in a spiritual guru in a meditative state.&nbsp;</p><img src="@@PLUGINFILE@@/Gamma.jpg" alt="Frontal Gamma" width="718" height="984" class="img-responsive atto_image_button_left"><br>
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