Diving Reflex (and freediving and sperm whales)

[dann]

Some of the claims Nestor makes are:
(...)
* Human heart rate lowers 25% on immersion in water
(...)

Doesn't seem to be the case:

Heart disease participants had the same response as HC participants to the three experimental conditions (no significant between-group differences in all HRV variables). STW (immersion) caused in both groups to increase HRV when compared to supine and STL.
Acute effects of water immersion on heart rate variability in participants with heart disease.

 

[lomiller]

Doesn't seem to be the case:

This appears to be looking at people standing in water. Dive reflex in humans appear to be triggered by holding your breath and immersing your face.

 

[dann]

But it only said "on immersion in water". At that point there was nothing about holding your breath etc.

 

[Andy_Ross]

This appears to be looking at people standing in water. Dive reflex in humans appear to be triggered by holding your breath and immersing your face.

Scuba divers find that their heart rate increases when they are under the surface. Lowering the rate is something you have to work at.

 

[lomiller]

So? Why is it essential for them to document every detail? It’s not a controversial subject and there are plenty of resources that more completely document the dive reflex
https://en.wikipedia.org/wiki/Diving_reflex

Scuba divers find that their heart rate increases when they are under the surface. Lowering the rate is something you have to work at.

SCUBA divers don’t hold their breath and mostly keep their face/nostrils dry.

 

[casebro]

Our brains have more than enough general processing power for simple echolocation. The fact that this ability can be evolved and specialized to do what dolphins and bats do is remarkable but the simple version doesn't seem all that impressive to me.



Our nerves operate via electrochemical signals not electromagnetic. There are no large conductors involved in which a magnetic field could be induced. This doesn't rule out magnetic fields interacting with sensory neurons or nerves but the effect would be really small. Microscopic bits of magnetic material would seem to be a more likely source for this sensory ability. IOW Unlike echolocation that can leverage existing brain+hearing magnetic field detection would seem to require an actual specialize sensory cells.

Gahead, read about magnetosensory and cryptochromes. Exactly those "actual specialize sensory cells"- in eyes.

 

[jimbob]

Indeed. Nestor doesn't actually make the claim IIRC that infants can actually swim (i.e. move themselves), though he kind of implies that the reflex might be linked to some sort of aquatic past. I'm more apt to believe in some sort of survival mechanism...the breath-holding part of the swim reflex, for example, is fairly important. Question in my mind is...why does it disappear?

I'm personally much more impressed by the echolocation - for example, the clip of the blind man apparently riding a bike. Given that our nerves, sensory neurons, and muscle cells all work by voltage-gated ion flow, it's not that much of a stretch to imagine that magnetic fields (of at least certain field strengths) might be discernible in some circumstances.

There was a touching BBC Radio4 programme about that guy

Batman and Ethan

Ethan was born blind. He's now a 10 year-old boy who collects sounds on his 51 dictaphones, composes music, and performs on stage in concerts. Until now he's been home-schooled, but last year he was offered a place at St Mary's Music School in Scotland - one of the best in the country. The problem is he struggles to get around.

This is where Batman comes in. His real name is Daniel Kish and like Ethan he's blind. He's a master of echolocation. He makes clicking noises - like a bat - to build a picture of the world around him. Neuroscientists have done experiments on him and found that he's managed to activate the visual part of his brain. He's taught people all over the world to "see through sound" and he's so good at it that he goes hiking, cycling and rock-climbing.

"Batman" (Daniel) comes to Scotland to spend 10 days with Ethan, to teach him echolocation and help him prepare for his new school. The documentary follows Ethan's progress as he learns from Daniel Kish. Listeners are introduced to the principles of echolocation, they follow Ethan practicing at home, on the train and at his new school. They're brought into Ethan's world, through music composed specially by Ethan, and they're with him on his birthday, on long walks in the Scottish hills, right through to his experience at school.

We follow Ethan up to his final day of term to find out how he's done, and see how he copes with his biggest challenge yet: playing an accordion solo with the orchestra at the school concert.

Produced and presented by Helena Merriman.

It's really interesting listening to Daniel Kish discussing how to navigate the school with Ethan ( avoid turning towards the attractively large echoey hall space, for example).

Well worth a listen if you have a few minutes.

 

[jimbob]

Again, though, you don’t have charge moving down a conductor. That isn’t how nerves and neurons work. Yes there is some physical movement of charged ions within a nerve cell and any movement of charge will create a tiny magnetic field but this is negligible. Your own link says it takes 100 000 simultaneous neurons firing to generate a measurable magnetic field.

This relationship is not symmetrical. Just because you can get a tiny magnetic field from an ion moving within a nerve cell when it fires, it does not mean that same nerve cell will fire in response to even a large magnetic field. This just not seem to be a viable mechanism for animals detecting magnetic fields, and research into exactly how animals detect magnetic fields is focusing on specific proteins that have the capability to function as a magnetic compass.
http://rsif.royalsocietypublishing.org/content/15/140/20180058

There is Transcranial Magnetic Stimulation

 

[BowlOfRed]

TMS is a rapidly changing magnetic field. Because it can induce electrical currents, the effects it has on neural tissues are very different than static fields.

 

[jimbob]

TMS is a rapidly changing magnetic field. Because it can induce electrical currents, the effects it has on neural tissues are very different than static fields.

True, and even then they have to be targeted - otherwise MRI scans would cause some interesting effects.

 

[Shadowdweller]

Again, though, you don’t have charge moving down a conductor. That isn’t how nerves and neurons work.

Of course action potentials don't work like electron flow down a wire. They don't need to.

Yes there is some physical movement of charged ions within a nerve cell and any movement of charge will create a tiny magnetic field but this is negligible. Your own link says it takes 100 000 simultaneous neurons firing to generate a measurable magnetic field.

Yeah that's about 2 cubic millimeters of CNS brain tissue, guy. Which is why MEG has diagnostic use. Of course, if we're discussing the ability to detect magnetic fields or be physiologically affected by them...then the magnetic field created by neurons themselves is irrelevant.

This relationship is not symmetrical. Just because you can get a tiny magnetic field from an ion moving within a nerve cell when it fires, it does not mean that same nerve cell will fire in response to even a large magnetic field. This just not seem to be a viable mechanism for animals detecting magnetic fields, and research into exactly how animals detect magnetic fields is focusing on specific proteins that have the capability to function as a magnetic compass.

Magnetic fields do not need to (directly) trigger depolarization to be discernible or affect the body. They might merely change physiological systems in ways that are detectable by the organism. Consider, for example, possible effects such as changing diffusion / transport rates, depolarization thresholds, protein conformation...The proteins that comprise the ion channels which allow AP propagation (i.e. sodium/potassium flow), for instance, have charged domains that might conceivably have altered functionality in the presence of a magnetic field. I already posted link to a peer-reviewed microscale study showing EEG responses to magnetic fields. Here's another examining the effects on calcium channels (responsible for a host of functions in the human body).

 

[lomiller]

TMS is a rapidly changing magnetic field. Because it can induce electrical currents, the effects it has on neural tissues are very different than static fields.

It's also using magnetic fields 50000 times stronger than the earths magnetic filed.

 

[Shadowdweller]

TMS is a rapidly changing magnetic field. Because it can induce electrical currents, the effects it has on neural tissues are very different than static fields.

Are we confining ourselves to discussion of static fields? I don't recall that having been previously specified. There are plenty of things (e.g. AC power lines, electric appliances) in modern society that produce non-static fields; although for reasonable applications, the earth's field would be considered static.

 

[Shadowdweller]

But it only said "on immersion in water". At that point there was nothing about holding your breath etc.

This is possibly an artifact of my having improperly translated my notes from the originating vid to something intelligible to others The clip (or more specifically Nestor) itself was talking about the Diving Reflex in the context of a 300-foot freedive. One hopes the guy was holding his breath...since the alternative is drowning.

 

[3point14]

There was a touching BBC Radio4 programme about that guy

Batman and Ethan



It's really interesting listening to Daniel Kish discussing how to navigate the school with Ethan ( avoid turning towards the attractively large echoey hall space, for example).

Well worth a listen if you have a few minutes.

David Clarke was blind from birth and was the England blind football team.

If I recall correctly he relied heavily on his ears, so much so that a scan revealed that large portions of his unused visual cortex had been co-opted by his hearing and was being used for 3d image processing. He said he didn't really need a noise, he could hear the surfaces around him being able to tell when, for instance, he passed a door in a corridor.

Amazing man.