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Depending upon its activity, the brain emits waves, which represent the summation of individual neurons firing. Are these waves electromagnetic waves?

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  • $\begingroup$ based on answers by robin kramer and christiaan, it seems that brainwaves are just eeg recordings, where eeg acts like an AC voltmeter. so, when eeg is showing an alpha wave, it does not mean that the brain is emitting any sort of wave in the corresponding frequency range, it just means that collective neural activity as captured by eeg takes form of alpha waves. is this what is going on? $\endgroup$ – Amit Maurya Jun 12 '16 at 23:21
  • $\begingroup$ Though Christiaan and Kramer's answers are very detailed and interesting, don't overlook bobby's, since brain waves indeed results in the creation of EM waves. $\endgroup$ – Silmathoron Jun 14 '16 at 14:45
  • $\begingroup$ physics.stackexchange.com/questions/314695/… $\endgroup$ – Fizz Nov 27 '17 at 19:15
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Short answer
Brain waves are not electromagnetic waves.

Long answer
Measured brain activity, as you already mentioned, is the result of individual neurons firing. The activity exists, in fact, of two parts. First of all, there are the action potentials (APs). APs are current flow within a neuron from one end to the other. The magnitude of these APs (and the summation of many) is so low however, that it is barely measurable.

The actual brain activity we can measure is the result of the second way of signal conduction: post-synaptic potentials as a result of neurotransmitters. (Pyramidal) Neurons communicate with each other through neurotransmitters, which are released from multiple synapses and flow to the axon of the next neuron. The release of the neurotransmitters causes a much larger potential difference that is conducted through different tissues (e.g. bones and skin). The activity that we measure with EEG is thus only the result of potential difference of the pyramidal neurons. Due to how electrical fields work, we are only able to measure the neurons oriented in right angles to the surface of the scalp (see the right picture).

Difference between EEG and MEG

A magnetic field cán also be measured though, but this is in fact the result of the flow in current. If electricity flows through a loop, a magnetic field is generated. Moreover, if there is a magnetic field, electrical current will be generated. This is how MEG works. If there is an electrical current, and you place these loops around the head, the magnetic field will be "caught". Then, in turn, this magnetic field will generated electricity in the MEG recording equipment, thereby recording electrical activity in the brain (See left part of the picture, there are two loops where the magnetic field goes through). The magnetic fields are orthogonal to the electrical fields (look for the Right-hand rule) and neurons that lie parallel to the scalp are more easily measurable. EEG and MEG complement each other thus, and combining them greatly improves localization of activity.

This is a quick and dirty explanation. For a better one, you may want to read the book of Luck: An Introduction to the Event-Related Potential Technique (2014), which explains it really nicely.

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  • $\begingroup$ So, you are saying brain waves are not emw even though electric and magnetic fields are associated with it? $\endgroup$ – Amit Maurya Jun 12 '16 at 18:10
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    $\begingroup$ Yes indeed. Brain activity IS not electromagnetic, it is electric. However, due the wonderful world of physics, electricity can make magnetic fields (and vice versa) and, therefore, are indeed associated with each other. $\endgroup$ – Robin Kramer Jun 12 '16 at 18:18
  • $\begingroup$ i think we have to answer following question to determine that for the original question - how does electrode of eeg catches the neural signal when it is not touching the neurons? $\endgroup$ – Amit Maurya Jun 12 '16 at 19:03
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    $\begingroup$ Electricity can be conducted through tissue. Just like copper, steel or saline water, different tissues in the body (skin, skull, fat and brain) conduct electricity too. So by placing the electrodes on the skin, electricity can flow from the brain, through the skull and skin to the electrodes. Often, some conductive gel is used as to improve the connection between skin and electrode (i.e. decrease impedance (resistance)) $\endgroup$ – Robin Kramer Jun 12 '16 at 19:09
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Short answer
Brainwaves are typically associated with the electroencephalogram, which is a signal mainly composed of potential differences generated in the superficial layers of the brain. Potential differences represent electric fields and do not represent electromagnetic (EM) radiation. EM radiation is build up of packets of energy (photons). EM radiation types are characterized and classified by their specific wavelengths, but this has nothing to do with brain waves.

Background
In addition to Robin Kramer's excellent answer I wish to approach this question from a more terminological approach, namely what are brainwaves?

Brainwave is a bit of a colloquial term. It is typically associated with the electroencephalogram (EEG). The EEG measures electrical potential differences, typically across the scalp (Fig. 1). This electrical activity emanating from the brain is displayed in the form of brainwaves. There are four categories of these brainwaves. These categories are based on frequency bands. The term frequency bands is a more formal term and refers to the way EEGs are typically analyzed, namely via Fourier transformation. Fourier transformation dissects any time-based signal into a number of well-defined sine waves, each with a characteristic frequency, expressed in cycles per second (i.e., Hz).

When the brain is aroused and actively engaged in mental activities, it generates beta waves. These beta waves are of relatively low amplitude, and are the fastest of the four different brainwaves (15 to 40 Hz frequency band). Alpha waves (9 - 14 Hz) represent non-arousal, are slower, and higher in amplitude. A person who has completed a task and sits down to rest is often in an alpha state. The next state, theta brainwaves (5 - 8 Hz), are typically of even greater amplitude and slower frequency. This frequency range is normally between 5 and 8 cycles a second. A person who has taken time off from a task and begins to daydream is often in a theta brainwave state. A person who is driving on a freeway, and discovers that they can't recall the last five miles, is often in a theta state induced by the process of freeway driving. The final brainwave state is delta (1.5 - 4 Hz). Here the brainwaves are of the greatest amplitude and slowest frequency. A deep, dreamless sleep is characterized by this frequency band. When we go for a night's sleep, brainwaves typically descend from beta, to alpha, to theta and finally, when we fall asleep, to delta (source: Sci Am, 1997).

EEG
Fig. 1. EEG traces. source: Sci Am, (1997)

EEG activity is measured via electrodes and these pick up a potential difference, or electric field. An electric field is not electromagnetic (EM), because it is not (necessarily) accompanied by a magnetic component. An electric field is generated everywhere where charge is separated. If no current flows, there is still an electric field, namely a static electric field. Only when current starts to flow a magnetic component is introduced (source: WHO). In the brain, static electric fields may exist, but EEG activity is typically evoked by repetitive, synchronized neural firings. Within the tissue, hence, current flows during action potential generation and hence there is definitely a magnetic component involved, this is measured with a magnetoencephalogram (MEG).

MEG measures magnetic fields and is typically not analyzed in the form of brainwaves but in the form of brain images (Fig. 2).

MEG
Fig. 2. MEG analysis. source: NYU Cognitive Neurophysiology Lab

MEG signals are also not EM radiation, but magnetic signals.

Finally, then what is EM radiation? EM radiation is a form of energy that is produced by oscillating electric and magnetic disturbance, or by the movement of electrically charged particles traveling through a vacuum or matter. The electric and magnetic fields come at right angles to each other and combined wave moves perpendicular to both magnetic and electric oscillating fields thus the disturbance. Electron radiation is released as photons, which are bundles of light energy that travel at the speed of light as quantized harmonic waves. This energy is then grouped into categories based on its wavelength into the electromagnetic spectrum. These electric and magnetic waves travel perpendicular to each other and have certain characteristics, including amplitude, wavelength, and frequency (Fig. 3).

EM spectrum
Fig. 3. EM spectrum. source: UC Davis

Importantly, EM radiation can either act as a wave or a particle, namely a photon. As a wave, it is represented by velocity, wavelength, and frequency. As a particle, EM is represented as a photon, which transports energy. Photons with higher energies produce shorter wavelengths and photons with lower energies produce longer wavelengths.

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  • $\begingroup$ There are not only four categories, see gamma. For beginner, the four categories that you mention are probably the most important but I think you should mention all there are. Also I think in different subfields people define the frequency ranges slighlty different although I don't have a source now (I just know that for example for Local Field Potentials theta can be between 6-10 Hz). Also I would be careful with the formulation "the brain generates beta waves", it"s all correlations that we know by now, no ? $\endgroup$ – awakenting Aug 13 '16 at 17:06
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If "brain waves" produce a time-varying electric potential as shown on the EEG, then as far as I know electromagnetic waves are present. I was taught that you cannot have a time varying electric potential without creating an electromagnetic wave. You can try browsing wiki explanation https://en.wikipedia.org/wiki/Maxwell%27s_equations, but the main idea is that a time varying electric field cannot exist without the presence of a time-varying magnetic field. I admit I have basically zero background knowledge on brainwaves, however after reading the two previous thorough answers I was left wondering why a brain wave would not fall into the category of electromagnetic waves.

"An electric field is not electromagnetic (EM), because it is not (necessarily) accompanied by a magnetic component." This is theoretically true for static electric fields, but I think static electric fields are similar to a "vacuum state" in the sense that they don't exist in real life or even if they did it would be really hard to measure without perturbing the system.

Waves are not static and, therefore, the EEG certainly shows a time-varying electric field.

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    $\begingroup$ Welcome to CogSci. Could you add your sources and the Maxwell reference so users can background read on your answer? $\endgroup$ – AliceD Jun 12 '16 at 21:43
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    $\begingroup$ An answer finishing off with a question is kind of not an answer, but a comment. What do you think is the answer to the question? Robin explained the physiological basis and concludes brainwaves are not EM, Christiaan targeted the terminology behind it and also concludes brain waves are not EM. What do you conclude? The contents of your answer follow Robin's closely. It would be interesting to see what your view on this question is. Basically, the question is more about physics than CogSci. Being unaware of your background, I can say a physical approach would be a valuable add-on. $\endgroup$ – AliceD Jun 13 '16 at 18:51
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    $\begingroup$ I need to correct you there. EEG does not measure EM radiation. As I discussed in my answer, EEG measures the voltages that is conducted with a particular speed (current) through bodily fluids. Even though EM radiation may be the result of this electrical flow, EEG does NOT record this. $\endgroup$ – Robin Kramer Jun 14 '16 at 17:00
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    $\begingroup$ I think you are missing the more fundamental picture. Any form of alternating current or voltage is an electromagnetic wave. Here's a great example of an electromagnetic wave that we can measure with a frequency <100Hz just like brainwaves...the electricity in your wall that you use to charge that smartphone. In most countries the frequency of the electrical supply is either 50 or 60Hz. Measure an electrical outlet with a voltmeter and you are doing the exact same thing that an EEG does, which is measuring the amplitude of an electromagnetic wave. $\endgroup$ – bobby Jun 15 '16 at 5:01
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    $\begingroup$ AC is an electromagnetic wave. You cannot separate the two and say that "other" EM waves of the same frequency accompany AC. Saying that eeg electrodes measure electric potential but not EM waves is similar to saying that measuring the height of a water parcel as a wave passes through is only measuring the height of the water, but not the wave itself. The water wave caused the water parcel to raise, and measuring the water height is measuring the amplitude of the wave. How else can you measure the amplitude of a wave? $\endgroup$ – bobby Jun 19 '16 at 17:28
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Strictly from a point of view in physics, there are only 4 fundamental interactions: gravitation, electromagnetic, weak interaction and strong interaction.

The weak and strong interactions only exist in sub-atomic, so they won't contribute anything to brainwave. The gravitation interaction, while theoretically affects, is extremely tiny to the point that it can be neglected either. Therefore, everything the brain does is electromagnetic. In fact, every chemical process can also be said to be purely electromagnetic.

I must emphasize this is strictly a physics point of view, because I know in other fields, like biology or neuroscience, it is impractical to group every form of electromagnetic interaction in one basket. Electric field, magnetic field, radiation, Van de Waals interaction, you name it, are different forms of electromagnetic interaction.

What can be quite confusing is that in biology or neuroscience, the term electromagnetic can be used for a form of such interaction: the co-existence of electric field and magnetic field. This is why we can say that electric field is not electromagnetic. This is, strictly from a physics point of view, wrong. However, this is just different interpretations of the term, so biologists and neuroscientists can safely use that statement.

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This is an important question for a number of reasons, not the least of which is the pervasive conflation of "brain waves" with EM or radio waves in popular media and even in some articles in Scientific American. The three top-voted answers at this point (June 2019) by Robin Kramer, AliceD, and bobby although apparently inconsistent, are all correct, but lack some detail that can resolve the apparent inconsistency.

To begin, as Robin states and AliceD implies, Brain waves are NOT electromagnetic (EM) waves; brain waves are the term given to the patterns of voltage differences measured between two electrodes connected to the three dimensional extracellular fluid matrix surrounding the brain (as shown beautifully by Robin). This matrix includes the skull and scalp of the subject, and since the skull has a high resistance, the current that eventually makes it to the scalp is quite small and produces a very small voltage as it flows through the somewhat resistive scalp between the two electrodes. During open skull surgery, the EEG recorded from the brain surface is 10-100 time larger as the current does not have to flow out through the skull to reach the electrodes and then back again. These voltage patterns of course go up and down, thus producing "waves" in the EEG record of voltage versus time as AliceD explains.

This is not the same sense of the term "wave" that is used in physics to describe wave phenomena; generally physicists talk about waves as solutions to differential wave equations, including Maxwell's equations. Only in the broadest sense of some possible periodicity of the phenomenon producing ups and downs in a graph of the phenomenon versus time can the commonality of these two senses of the word "wave" be identified. Note, however, that physicist's solutions to wave equations can be quite general, and include any combination of solution functions that take as arguments (ax+bt) and (ax-bt) representing forward and backwards traveling solutions. Hence, a square pulse will solve wave equations, and given that any realistic signal has a Fourier representation, any signal can be said to be comprised of a weighted sum of sine and cosine "waves" as described by AliceD, even if the signal itself is not periodic.

EM waves are solutions to Maxwell's equations that carry energy through space by means of changing electric and magnetic fields that can travel long distances from where they are launched and are associated with far-field energy. This far-field energy is no longer affected by its source, nor does its fate affect its source. This is different than the energy in the electric and magnetic fields related to the current flow in the extracellular matrix; this is called the near-field, and it comprises the motive power that drives the current flow. Attention to details is important here; EEGs do not record electric fields, they record differences in potential. Potential is a scalar field with a single numerical value at each point in space and no absolute zero point - hence having to always measure the difference in voltage (potential) between two points and to have connections to the extracellular fluid matrix circuit, whereas the electric field is a vector field with a magnitude and direction at each point in space. The electric field is the gradient of the potential, and this is the direction that the current will flow in isotropic extracellular fluid. Changing the potential at points in the extracellular matrix will change the near-field electric field and thus the three dimensional pattern of current flow and any recorded potential differences. Brain waves are these latter potential differences due to the near-field energy in the electric and magnetic fields, and separate from the far field effects of radiated energy in the form of EM waves.

Now, bobby points out that changing potential differences representing brain waves imply changing electric fields that, as Maxwell says, produces changing magnetic fields, which, in turn generates a changing electric field, etc - and we're off to the races: an EM wave is launched! Or is it?

One needs a device called an antenna to transduce a changing voltage/current into and EM wave, and a very basic rule for antennas is that they only start converting significant amounts of energy when the size of the antenna approaches 1/4 the wavelength of the signal being radiated. So let's see how big our antenna would need to be for a 10 Hz alpha wave to be launched out of our scalp. Since EM waves travel at the speed of light, or 300,000,000 m/s, our scalp would have to be 75,000,000 meters in size! I don't have the equations here, but it's pretty obvious that essentially zero energy at 10 Hz is going to be radiated. And if one wanted to pick up that signal, the receiving antenna would have to be equally large! Seventy five Megameters is pretty damn big.

This is why the EEG electrodes have to touch the scalp or otherwise connect to the actual circuit in which current is flowing rather than than just be placed nearby to pick up radiated EM energy from the brain. And while it's true a number of tricks can be pulled (as is done in cell phones dielectric antennas) to reduce this size by maybe a factor of ten, even for 100Hz or 1000Hz signals, virtually no energy is going to radiate from the scalp, nor will EM waves be picked up and converted into changing potentials on the scalp from the EM milieu around us. Cell phones can be small because they utilize signals in the range of 3 GHz where 1/4 of a wavelength is about 2.5 cm, or an inch.

So, even though there could be EM waves produced by brain "waves", practically speaking, it doesn't happen, and looking in detail at how EM wave are radiated reveals that the brain "wave" is, in fact, a different phenomenon from any EM wave that it might be associated with or generate.

Perhaps the most succinct way to pinpoint the difference is to note that EM waves consist of packets of energy propagating through space via self-regenerating changing electric and magnetic fields that have units of volts/meter and amps/meter, while brain "waves" are difference in voltages between two points on the scalp measured in Volts - note that they have different units. With brain "waves", essentially no energy is leaving the scalp and radiating into space because the frequencies are too low and the scalp is far to small to act as an effective antenna to convert them into EM waves.

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Brain 'waves' by nature are EM waves, albeit very weak and in the range of 1-100hz, which for waves, is a very weak oscillating cycle in the hundreds per second. For comparison, a standard EM radio wave will oscillate in MHZ range at millions of cycles per second. That being said, the technicality is that any travelling electric current will generate a concurrent magnetic field, and be electromagnetic in nature. New research in Neuroscience is coming forward to better understand the electromagnetic aspect of brain waves. In the EM realm they are incredibly weak and without correct shielding from other EM radiation, pretty much impossible to detect. However, studies in mice have shown their brain to have an electric field that can help brain waves propagate, and any travelling electric current such as in neurons firing will be electromagnetic in nature because an electric current cannot exist without the accompanying magnetic field.

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Some of the information contained in this post requires additional references. Please edit to add citations to reliable sources that support the assertions made here. Unsourced material may be disputed or deleted.

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    $\begingroup$ Welcome. New research in Neuroscience -- You should cite those papers in your answer. In general we ask answers to be sourced, preferably with scientific journal papers. $\endgroup$ – AliceD Jan 5 at 20:08
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My belief of electromagnetic brain waves such as today prosthetics technology that is just for fronting in today's society with smart prosthetics moving with the thought of process of your brain hooked into your electromagnetic nervous system. Are brain waves electromagnetic frequency generator 10 to 100 cycles per minute of electromagnetic frequencies or other words electromagnetic static.. flowing through our neurons and nerve endings that give us a full word mobility of motion. The conscious of life is electromagnetic frequencies of our brain wave electromagnetic static frequencies that generate movement and thought site feeling all our emotions... There are electromagnetic fields around us that interfere with our surroundings. The brain waves much lower frequency of electrical magnetic pulses.. so if Prosthetics can be tapped into are immune system of nerves and electromagnetic or should I say electrostatic static field of ones human ability.. so the question here would be if Prosthetics can tap into are electromagnetic state of brain waves. That are electrical and nature such as everything else around us how is it that are brain waves are not electromagnetic. But just at a lower frequency of rate of pulse of electromagnetic frequencies at a different rate of speed and frequency that is detectable in measurable

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