3 ms·

main article link: https://physoc.onlinelibrary.wiley.com/doi/10.1113/JP276904 https://physoc.onlinelibrary.wiley.com/doi/10.1113/JP276904 It seems as though t

main article link: https://physoc.onlinelibrary.wiley.com/doi/10.1113/JP276904 https://physoc.onlinelibrary.wiley.com/doi/10.1113/JP276904 It seems as though the authors are advocating for the role of extracellular electric fields to enable spiking. This is known as ephaptic coupling, which is a fairly well studied phenomenon, but it is unknown the degree to which it contributes to standard computations and processing within different neural systems. https://en.wikipedia.org/wiki/Ephaptic_coupling https://en.wikipedia.org/wiki/Ephaptic_coupling

acqq 8y ago
> it is unknown the degree to which it contributes to standard computations and processing within different neural systems And that is not even the topic of the article: "the present study shows that the in-vitro slow periodic activity, mediated by the NMDA spikes, can propagate non-synaptically by a mechanism consistent with ephaptic coupling. This study implies that the effect of ephaptic coupling could play an important role in the propagation of neural activity under normal physiological conditions as well as pathological situations." Important: "slow periodic activity" Also important: it's in vitro: https://en.wikipedia.org/wiki/In_vitro https://en.wikipedia.org/wiki/In_vitro "In vitro (meaning: in the glass) studies are performed with microorganisms, cells, or biological molecules outside their normal biological context. Colloquially called "test-tube experiments"..." What's new: "Results support the hypothesis that endogenous electric fields, previously thought to be too small to trigger neural activity, play a significant role in the self-propagation of slow periodic activity in the hippocampus." In short, they claim to have proved that under some special conditions the propagation can happen even by what was believed to be too small fields. But as it's the first paper about that, it's reasonable for the observers to wait for other scientists to repeat the experiment and review the details of it... before making any conclusions.
bayesian_horse 8y ago
The point is that the field strengths is too low or the distance to great for ephaptic coupling to occur.
DoctorOetker 8y ago
the abstract was mentioned in this post https://news.ycombinator.com/user?id=SubiculumCode https://news.ycombinator.com/user?id=SubiculumCode > ...low‐frequency periodic activity (<1 Hz)... propagate with speeds around 0.1 m s−1 so thats a wavelength of ... at least 10cm! not much information density here... this is probably the reason nobody is interested much in these effects. Even if they can chaotically influence the state of the system, it won't contain much useful information...
- candiodari 8y ago
  Okay but you have to keep in mind that there are multiple waves, and what you might use them for. Think of how a sonar works. Sonars must associate and compare the timing of events, just like neurons. They use as many different frequencies for that as possible (used to be 4-8 frequencies but the state of the art is presumably much more) Let's say I have brainwaves at 0.5Hz, 4Hz, 8Hz and 20Hz wave. And let's assume they are all non-harmonic. If you have an event, and you can quickly inspect the position and phase of all these waves, you now have an extremely accurate and long-period reference for the time the event occurred (think of the individual waves as the numbers on a clock). So the accuracy would be a decent multiple of the highest frequency, so let's say 20-50ms resolution. And the repeat is the multiple of all the wavelengths, so this would give neurons a trivial way to understand or plan events up to 640 seconds away from the current moment, as well as an easy way to refer to the exact moment a prediction will come true, and how different events relate to eachother in time. It's brilliant.
- mattkrause 8y ago
  One theory is that the waves themselves don’t carry much information, but set the stage for other kinds of transmission or computation. In the rodent hippocampus, for example, theta oscillations (3-7ish Hz) don’t tell you much about the animals’ spatial position. The spiking rate of place cells contains some information about where the animal is, but it’s fairly coarse. However, combining spiking and the phase of the slow oscillation (e.g., cell is firing at the trough vs peak) provides much more precise information about where the rat is. A related idea is that oscillations help route information by alternatingly facilitating and suppressing different areas. At one phase of the oscillation, information might preferentially flow from visual areas to higher-level areas. At another, the visual input might be suppressed while memory structures get “their turn to talk.”

acqq 8y ago

> it is unknown the degree to which it contributes to standard computations and processing within different neural systems And that is not even the topic of the article: "the present study shows that the in-vitro slow periodic activity, mediated by the NMDA spikes, can propagate non-synaptically by a mechanism consistent with ephaptic coupling. This study implies that the effect of ephaptic coupling could play an important role in the propagation of neural activity under normal physiological conditions as well as pathological situations." Important: "slow periodic activity" Also important: it's in vitro: https://en.wikipedia.org/wiki/In_vitro https://en.wikipedia.org/wiki/In_vitro "In vitro (meaning: in the glass) studies are performed with microorganisms, cells, or biological molecules outside their normal biological context. Colloquially called "test-tube experiments"..." What's new: "Results support the hypothesis that endogenous electric fields, previously thought to be too small to trigger neural activity, play a significant role in the self-propagation of slow periodic activity in the hippocampus." In short, they claim to have proved that under some special conditions the propagation can happen even by what was believed to be too small fields. But as it's the first paper about that, it's reasonable for the observers to wait for other scientists to repeat the experiment and review the details of it... before making any conclusions.

bayesian_horse 8y ago

The point is that the field strengths is too low or the distance to great for ephaptic coupling to occur.

DoctorOetker 8y ago

the abstract was mentioned in this post https://news.ycombinator.com/user?id=SubiculumCode https://news.ycombinator.com/user?id=SubiculumCode > ...low‐frequency periodic activity (<1 Hz)... propagate with speeds around 0.1 m s−1 so thats a wavelength of ... at least 10cm! not much information density here... this is probably the reason nobody is interested much in these effects. Even if they can chaotically influence the state of the system, it won't contain much useful information...

candiodari 8y ago
Okay but you have to keep in mind that there are multiple waves, and what you might use them for. Think of how a sonar works. Sonars must associate and compare the timing of events, just like neurons. They use as many different frequencies for that as possible (used to be 4-8 frequencies but the state of the art is presumably much more) Let's say I have brainwaves at 0.5Hz, 4Hz, 8Hz and 20Hz wave. And let's assume they are all non-harmonic. If you have an event, and you can quickly inspect the position and phase of all these waves, you now have an extremely accurate and long-period reference for the time the event occurred (think of the individual waves as the numbers on a clock). So the accuracy would be a decent multiple of the highest frequency, so let's say 20-50ms resolution. And the repeat is the multiple of all the wavelengths, so this would give neurons a trivial way to understand or plan events up to 640 seconds away from the current moment, as well as an easy way to refer to the exact moment a prediction will come true, and how different events relate to eachother in time. It's brilliant.
mattkrause 8y ago
One theory is that the waves themselves don’t carry much information, but set the stage for other kinds of transmission or computation. In the rodent hippocampus, for example, theta oscillations (3-7ish Hz) don’t tell you much about the animals’ spatial position. The spiking rate of place cells contains some information about where the animal is, but it’s fairly coarse. However, combining spiking and the phase of the slow oscillation (e.g., cell is firing at the trough vs peak) provides much more precise information about where the rat is. A related idea is that oscillations help route information by alternatingly facilitating and suppressing different areas. At one phase of the oscillation, information might preferentially flow from visual areas to higher-level areas. At another, the visual input might be suppressed while memory structures get “their turn to talk.”