Can EM waves stimulate neurons?

[Sibilo]

I'm posting this topic after an invitation to do so. So considering that transcranial magnetic stimulation which operates in frequencies and therefore through EM induction can excite neurons, then can an EM wave also excite neurons?

 

[Baluncore]

Only VLF EM waves below about 1 kHz that pass through the body, and induce a current in the body electrolyte, will excite neurons. Deep RF burns, due to dielectric heating, are more likely with higher frequencies.

The chemical balance of neurotransmitters in the synapses may be upset, in the same way that an AC electric shock causes muscle cramping, followed by muscle weakness or paralysis.

 

[Sibilo]

Only VLF EM waves below about 1 kHz that pass through the body, and induce a current in the body electrolyte, will excite neurons. Deep RF burns, due to dielectric heating, are more likely with higher frequencies.

The chemical balance of neurotransmitters in the synapses may be upset, in the same way that an AC electric shock causes muscle cramping, followed by muscle weakness or paralysis.

thanks Baluncore for the answer, this is one of those questions that make you think also because we are talking about the same medal. then if I'm not mistaken, a few years ago scientists created electromagnetic wave brain stimulation. Then also logically, EM waves that disturb a receiving antenna induce an electric current. Balcuncore, however, I would like to know why heating occurs at frequencies greater than 1Khz? I knew that this effect happened at millimeter waves (Frey effect) and not at such long wavelengths, what do you think?

 

[Baluncore]

I knew that this effect happened at millimeter waves (Frey effect) and not at such long wavelengths, what do you think?

Dielectric heating of flesh is called diathermy. HF radiation on an ISM band is used for cauterising surgical wounds. Microwaves, with short wavelengths, tend to be radiated into the workplace environment. A diathermy "wand" is deliberately mismatched to provide a high RF electric field at the surface, with minimum antenna radiation, which is done to protect the operator.
https://en.wikipedia.org/wiki/Diathermy

Any frequency below 1 kHz will have a wavelength longer than 300 km. The electric field gradient will be low, and will be short-circuited by the surface tissues and bone. Only a low frequency magnetic field will penetrate the tissue, which explains why a coil with a pulsed current, is used to induce an ion current, for transcranial magnetic stimulation.

Since ion velocity in a tissue electrolyte is relatively slow, the frequency must be kept low, in order to actually transport ions across neurological boundaries or membranes in the tissue. HF radiation will just average out at net-zero ion transport, with maximum heating.

 

[Sibilo]

Dielectric heating of flesh is called diathermy. HF radiation on an ISM band is used for cauterising surgical wounds. Microwaves, with short wavelengths, tend to be radiated into the workplace environment. A diathermy "wand" is deliberately mismatched to provide a high RF electric field at the surface, with minimum antenna radiation, which is done to protect the operator.
https://en.wikipedia.org/wiki/Diathermy

Any frequency below 1 kHz will have a wavelength longer than 300 km. The electric field gradient will be low, and will be short-circuited by the surface tissues and bone. Only a low frequency magnetic field will penetrate the tissue, which explains why a coil with a pulsed current, is used to induce an ion current, for transcranial magnetic stimulation.

Since ion velocity in a tissue electrolyte is relatively slow, the frequency must be kept low, in order to actually transport ions across neurological boundaries or membranes in the tissue. HF radiation will just average out at net-zero ion transport, with maximum heating.

in recent days I read an article that is right for our case, I put the link below, in which multiple electric fields of frequencies higher than khz could be enveloped at a target frequency for example 10 hz in the interested area. so by studying this case is it possible to simulate it also with em waves?
https://www.nature.com/articles/s41593-023-01456-8

 

[Baluncore]

The technique referred to in that paper, employs pairs of electrodes to establish ion currents in the head. By crossing the paths of those currents, having slightly different kHz frequencies, they claim that the hippocampus can be stimulated by the difference frequency.

What they call a difference frequency, is actually an alternating constructive - destructive beat between the two sine waves, as their phase slide past each other. The sum of the two fields still has the kHz average carrier frequency, but it is being AM modulated (sinusoidally) at the difference frequency. For that reason, I would not expect it to be different to a single source of 1 kHz, pulsed sinusoidally, ten times per second.

The fanciful idea that they can focus the electric field to the hippocampus is I think misplaced. Ion currents do not flow like narrow rivers through an electrolyte, they spread out to flow through the bulk volume available. The two fields of ions will interact throughout the brain, not just at the midpoint where the central axis of one, crosses the central axis of the other.

I do not see any value in that paper.

 

[Sibilo]

The technique referred to in that paper, employs pairs of electrodes to establish ion currents in the head. By crossing the paths of those currents, having slightly different kHz frequencies, they claim that the hippocampus can be stimulated by the difference frequency.

What they call a difference frequency, is actually an alternating constructive - destructive beat between the two sine waves, as their phase slide past each other. The sum of the two fields still has the kHz average carrier frequency, but it is being AM modulated (sinusoidally) at the difference frequency. For that reason, I would not expect it to be different to a single source of 1 kHz, pulsed sinusoidally, ten times per second.

The fanciful idea that they can focus the electric field to the hippocampus is I think misplaced. Ion currents do not flow like narrow rivers through an electrolyte, they spread out to flow through the bulk volume available. The two fields of ions will interact throughout the brain, not just at the midpoint where the central axis of one, crosses the central axis of the other.

I do not see any value in that paper.

nderstand when you say that being AM modulated, it will be as if there were a single source pulsed 10 times, in this case the frequency of the difference is a physical effect and is called "third sound of Tartini" and has nothing to do with it with modulation, in fact I really believe that there is no modulation. But I want to know if 2 EM waves can cross each other and obtain the same effect, even if with enormous wavelengths?

 

[Vanadium 50]

Clearly nobody in this thread has ever received an RF burn. Those neurons will be letting you know they aren't happy,

 

[Sibilo]

Clearly nobody in this thread has ever received an RF burn. Those neurons will be letting you know they aren't happy,

yes, in fact, neither do I , mobile phones operate above 1ghz and nothing happens, at low powers, but now I want to know clearly whether EM waves can excite neurons or large areas of the brain, below 1khz it is possible as Baluncore said, but which values must be respected and at what maximum frequency?

 

[Vanadium 50]

Below 1 kHz they really are not waves in the sense you are likely thinking of. The wavelengths are hundreds of miles. Furthermore, the energy of such radiation is way, way lower than what you get from just thermal radiation: even detecting a 1 kHz signal on top of that takes work.

 

[Baluncore]

... and has nothing to do with it with modulation, in fact I really believe that there is no modulation.

The linear addition of two, close in frequency, sine waves, does NOT produce a DC component as would a diode detector, nor is there energy present at the difference frequency.

The energy delivered appears in the time domain to be a carrier, AM modulated by a rectified sine wave of half the difference frequency. Addition is not multiplication, and the carrier phase is different to true AM. It is not true modulation, it is a beat. The thermal energy delivered is however, pulsed at the beat frequency.

But I want to know if 2 EM waves can cross each other and obtain the same effect, even if with enormous wavelengths?

The same effect as what?
If the tissue is linear, the additive beat signal still contains energy at only the two close carrier frequencies.

 

[Sibilo]

The linear addition of two, close in frequency, sine waves, does NOT produce a DC component as would a diode detector, nor is there energy present at the difference frequency.

The energy delivered appears in the time domain to be a carrier, AM modulated by a rectified sine wave of half the difference frequency. Addition is not multiplication, and the carrier phase is different to true AM. It is not true modulation, it is a beat. The thermal energy delivered is however, pulsed at the beat frequency. The same effect as what?
If the tissue is linear, the additive beat signal still contains energy at only the two close carrier frequencies.

so baluncore I don't think I understood everything perhaps because of the translation, in any case yes our body is not a cat's whisker radio and therefore cannot demodulate a signal, but in fact there is nothing to demodulate as you said since it is only a beat. but then I didn't understand the last part about the linear fabric

 

[Sibilo]

The energy delivered appears in the time domain to be a carrier, AM modulated by a rectified sine wave of half the difference frequency.

"The delivered energy appears in the time domain as a carrier, AM modulated by a rectified sine wave of half the differential frequency" sorry I didn't understand this part

 

[Baluncore]

I don't think I understood everything perhaps because of the translation, ...

What translation? What is your home language.

"The delivered energy appears in the time domain as a carrier, AM modulated by a rectified sine wave of half the differential frequency" sorry I didn't understand this part

Here is the linear sum of two 1 volt sine waves 2.000 kHz and 2.005 kHz.

Here is the detail where they are constructive, in phase.

And here they are destructive, out of phase.
Exact cancellation to zero, can only occur if the waves have identical amplitudes.

 

[Sibilo]

What translation? What is your home language.

Here is the linear sum of two sine waves 2.000 kHz and 2.005 kHz.
View attachment 335132
Here is the detail where they are constructive, in phase.
View attachment 335133
And here they are destructive, out of phase.
Exact cancellation to zero, can only occur if the waves have identical amplitudes.
View attachment 335134

I'm Italian and so Google Translate sometimes doesn't allow me to understand the concepts well. However, I just want to know if an EM wave can have the same excitation effects as magnetic stimulation. In your answer you also state that the energy delivered is in the time field of a carrier and therefore pulsed. also because in this case there is no need to straighten anything, given that there is no "information" in the wave but rather the simple beat at 10hz. so in my opinion an EM wave can excite the neurons given that it is a simple depolarization of the ionic channels, so in summary what do you think?

 

[Baluncore]

However, I just want to know if an EM wave can have the same excitation effects as magnetic stimulation.

No. They are different effects.
What you call an EM wave, is actually an ionic current from skin electrodes, that flows through the tissue.
Magnetic stimulation penetrates the cranium to induce ion currents, within the brain.

In your answer you also state that the energy delivered is in the time field of a carrier and therefore pulsed.

If the stimulation was by heating, then the stimulation is pulsed by the 5 Hz beat. The power used was insufficient to significantly heat the tissue, so local heating would not stimulate the brain at 5 Hz. Higher power could heat the brain, but the thermal time constant would attenuate the 5 Hz signal, so there would only be, a general cooking of the tissue.

If the stimulation is by ionic currents, then the beating 2 kHz currents, have too high a frequency to have a strong stimulating effect.

... so in my opinion an EM wave can excite the neurons given that it is a simple depolarization of the ionic channels, ...

High currents at 2 kHz may depolarise ion channels, but that will not stimulate a specific part of the brain. The small currents used, 1 mA, are unlikely to have an effect at 2 kHz.

The test subject was a cadaver, not a living person, so we do not have a report from the patient/victim. We do not know if the treatment stimulated anything, or made them feel different.

so in summary what do you think?

The paper is a confoundation of unrealistic expectations. It is a distraction from reality.
The stimulation is NOT really by EM fields, but by ionic currents from surface electrodes.
Narrow rivers of ionic current do not exist, so will NOT focus the effect onto a small region of tissue.
The 2 kHz current is TOO high a frequency, to directly stimulate neurons.
There is NO effective, or real 5 Hz beat in the brain. NO ionic beat, NO thermal beat.

Do not be distracted. Keep using magnetic stimulation.

 

[berkeman]

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