
Discovering a New Form of Communication in the Brain - oikos
https://thedaily.case.edu/discovering-a-new-form-of-communication-in-the-brain/
======
SubiculumCode
Abstract

Slow periodic activity in the longitudinal hippocampal slice can
self‐propagate non‐synaptically by a mechanism consistent with ephaptic
coupling

Slow oscillations are a standard feature observed in the cortex and the
hippocampus during slow wave sleep. Slow oscillations are characterized by
low‐frequency periodic activity (<1 Hz) and are thought to be related to
memory consolidation. These waves are assumed to be a reflection of the
underlying neural activity, but it is not known if they can, by themselves, be
self‐sustained and propagate. Previous studies have shown that slow periodic
activity can be reproduced in the in vitro preparation to mimic in vivo slow
oscillations. Slow periodic activity can propagate with speeds around 0.1 m
s−1 and be modulated by weak electric fields. In the present study, we show
that slow periodic activity in the longitudinal hippocampal slice is a
self‐regenerating wave which can propagate with and without chemical or
electrical synaptic transmission at the same speeds. We also show that
applying local extracellular electric fields can modulate or even block the
propagation of this wave in both in silico and in vitro models. Our results
support the notion that ephaptic coupling plays a significant role in the
propagation of the slow hippocampal periodic activity. Moreover, these results
indicate that a neural network can give rise to sustained self‐propagating
waves by ephaptic coupling, suggesting a novel propagation mechanism for
neural activity under normal physiological conditions.

Abstract isn't so flamboyant as the linked article

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quickthrower2
Does anyone know, how does the strength of these fields compare to the
strength of the field in the brain from a wifi router at a reasonable
distance? Why doesn’t all the comms gear mess with our thought processes?

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tbenst
Neuroscience PhD student here. The skull acts as a low-pass filter. EEG
recordings are typically low pass filtered at 70Hz or lower for example. This
is why you can’t decode eg speech from a EEG: the neural encoding is at a
higher frequency band than can be recorded. Even though the signal is much
stronger, digital comms equipment is orders of magnitude higher in frequency
and does not penetrate the skull well.

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est31
What about the radio signal used for MRI imaging, is it blocked by the skull
as well? Or is it just strong enough to be able to penetrate the skull?

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tbenst
fMRIs use a crazy strong magnetic field—typically >= 3 Tesla. The signal that
is measured is not electrical but rather the blood oxygen level. Effectively,
this is a correlate of the metabolic expenditure of nearby neurons. Wass it is
also like a low-pass filter except here it’s more like 0.5 Hz or slower. On
the plus, you get much improved spatial resolution

~~~
est31
MRIs use two magnetic fields, a static one and a dynamic one. And they use a
radio signal according to the larmor frequency to excite the spin of the
atoms. I was wondering about that radio signal component.

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acrefoot
Looking at the paper [0], particularly Figure 4, it looks like they cut slices
then stick them back together again. This allows the signal to propagate
(4.B).

But when a gap of 400 microns is added (4.C), the signal doesn't propagate.

I'm sure that the actual cutting causes some damage, and perfect realignment
is unlikely, but I'm not sure how this is conclusive of ephaptic coupling, or
how it eliminates the possibility of electrical or chemical communication by
synapse, gap junction, or axonal transmission.

[0]
[https://physoc.onlinelibrary.wiley.com/doi/10.1113/JP276904](https://physoc.onlinelibrary.wiley.com/doi/10.1113/JP276904)

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laser
A synaptic cleft is like 40 nm, or 10,000x smaller than 400 microns, so it
seems the scales of typical communication are enough orders of magnitude
smaller to be an implausible explanation?

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acrefoot
If the signal transmission worked at 400 microns, I would say that your
feature size argument would be a good reason to consider other explanations,
but they explicitly show that such a gap _prevents_ the signal from being
transmitted.

Instead, the transmissible gap is poorly characterized—-they cut then stick
the slices back together. Depending on how clean the cut is, the gap could be
quite small. Yet they argue that this unknown small distance (which presumably
still contains a fluid interface) is enough to eliminate the usual
explanations. That argument feels undersupported to me.

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laser
Ah, I was under the assumption that 400 microns was implied to be at least
within an order of magnitude of the threshold, so for example I assumed the
signal transmission worked at at least 40 microns, which is still 1000x the
synaptic cleft. If there's no information about where the cut-off is, only
some upper limit, perhaps even due to the lack of precision in the technique
itself, then this does seem pretty questionable, indeed.

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dr_dshiv
When the electrical field potential changes, it changes the probability of
neural firing. It's called ephatic coupling. Brain waves (local field
potential) aren't just the measured average of the neural firing, but are a
signal propagating force. This supports synchronization through entrainment
and other resonance effects that are well characterized. Not sure why this is
new, but it is great to see it in the news.

~~~
dr_dshiv
Here is the reference:
[https://www.nature.com/articles/nn.2727](https://www.nature.com/articles/nn.2727)

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sircalvin
Is this different from retinal waves?
[https://en.wikipedia.org/wiki/Retinal_waves](https://en.wikipedia.org/wiki/Retinal_waves)

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tbenst
Very different. Retinal waves are a developmental phenomena and use action
potentials for propagation. The study at hand attempts to disrupt all action
potential transmission.

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anfractuosity
Does the method that Transcranial magnetic stimulation effects neurons relate
to this out of interest?

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Praxey
I wonder if this validates the Orchestrated Objective Reduction theory of
consciousness pioneered by Roger Penrose and Stuart Hameroff. Seems like it
would.

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gliptic
What does this have to do with supposed qubits inside neurons?

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Praxey
A bit technical, but some of the most vocal critics of Orch-OR claimed there
was no way that quantum states could orchestrate across synapses or between
neurons. This quite interesting finding argues otherwise.

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gliptic
I don't see how this enables any orchestration that other signals do not.
There's still decoherence. It must have been among the weakest objections to
Orch-OR. Knocking down the weakest counter-argument (which sounds like a
strawman) doesn't really bolster the hypothesis in any way.

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cr0sh
I noted this on the other thread about this discovery:

I wonder if this might be a basis for a biological means for
"backpropagation"?

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kylek
Is this really new? I always thought that this was essentially the implication
of the discovery of standing-waves in the brain

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lizardwalk5
what does that mean? is that a form of explanation for why we are more
creative or able to solve problems in our sleep (or after sleep)?

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buboard
it means that neurons can 'transmit' a spike to their immediately neighboring
neurons even without chemical synaptic transmission (which is the norm). i
cant think of a relation to sleep but there could be one.

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punibloky
never reported publicly anyway...underpinning of psychic phenomena perhaps?

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DoctorOetker
>Until now, there were three known ways that neurons “talk” to each other in
the brain: via synaptic transmission, axonal transmission and what are known
as “gap junctions” between the neurons.

I know about _chemical synapses_ (the "usual" synapses with gain, and which we
model with weights in artificial neural networks, and which transmit
information in forward mode), I also know about _electrical synapses_ (fast,
no gain, bidirectional, possibly mediator of the backpropagation signal?) but
I don't know what they refer to with "axonal transmission" ? surely they don't
just mean pulse propagation along the axon, can someone point me to the
accepted mechanism of axonal transmission across neurons? from cell body to
synapse is just transmission line along the same neuron...

also correlation is not necessarily propagation, consider for example shining
a laser dot on a distant wall, and rotating the beam such that the spot moves
faster than light: this is perfectly possible, but no physical signal is
moving faster than light, rather the dot at some initial time and the dot at a
later time are correlated, but are both the result of a laser reflecting of a
rotating mirror.

in order to eliminate a mutual cause, you dont make a local cut in some
neuronal tissue, you fully separate the tissue, and then measure their
electrical activity (preferably optically using a nematic liquid crystal as
they used in the past to inspect voltage levels on chips under microscopes)
while mounted on micron precision translation stage, and starting from a
distance, slowly have the samples approach and measure their correlation, and
do the same experiment without a neuron culture, because the correlation may
be due to stray electric fields from the environment (another common cause,
like the laser for the lightspeed dots)

use 2 different wavelengths (and corresponding filters at the detectors) of
light to measure the optical activity of the nematic liquid crystal sensors,
in order to make sure no light is leaking through...

According to wikipedia
[https://en.wikipedia.org/wiki/Axonal_transport](https://en.wikipedia.org/wiki/Axonal_transport)
:

>Since some axons are on the order of meters long, neurons cannot rely on
diffusion to carry products of the nucleus and organelles to the end of their
axons.

and:

>Vesicular cargoes move relatively fast (50–400 mm/day) whereas transport of
soluble (cytosolic) and cytoskeletal proteins takes much longer (moving at
less than 8 mm/day).

note that the flow of material in axonal transport is retrograde (i.e. in the
opposite direction of pulse transmission), so any feedback, adjoint
sensitivity or backpropagation signal - if it exists - to implement Automatic
Differentiation in a physical manner, might move at such speeds. I don't know
the typical axon lengths (please tell me if you know or can refer me to
measured distributions of axon length), but this maximum of about 1000mm
implies 125 days (8mm/day) or 2.5 days (400mm/day). If we assume the dimension
of the brain as a typical axon length i.e. 10cm = 100mm then this becomes 12.5
days (400mm/day) and 0.25 days or six hours (8mm/day). For 1cm we have 30
hours (8mm/d) and 36 minutes (400mm/d). For 1cm to 10cm typical axon lengths
and shorter indeed seem like the kind of time frame of learning, i.e. the
weights may be modified during sleep, and the delay line of materials
undergoing axonal transport in _each axon_ contain echoes or memories of
synaptic activity during the day.

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Eyght
_You are only coming through in waves_

~~~
quickthrower2
Nice Scissor Sisters reference :-)

~~~
ilteris
I am not familiar with scissors sisters but I know that line from Pink Floyd.

~~~
quickthrower2
They did a cover of the same song. Worth a listen, it's completely different.

