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MRI Magnets Cause Nystagmus

Unknown Lamer posted more than 2 years ago | from the twirling-twirling-toward-vomit dept.

Medicine 120

Hitting the main page for the first time, tibit writes "In an interesting twist on 'it's so old it's new again,' Johns Hopkins researchers led by Dale Roberts found what must have been causing much confusion for doctors the world over: strong external magnetic fields can stimulate the semicircular canals, causing vertigo and nystagmus (pendular eye motion). It's a textbook case of the Lorentz force in action: our angular rate gyros, the semicircular canals in the middle ear, filled with endolymph, have a ionic current flowing across. In a magnetic field, the current produces a force that pushes the lymph along the channel, causing stimulation of the cupula — a pressure sensor at the end of the channel. This is interpreted by the brain as rotation of the head in space, and causes a nystagmus that's supposed to stabilize the image on the retina. Of course, the subject is laying down and not spinning in space, and the mismatch between inertial measurements coming from the ear and the real situation causes vertigo."

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120 comments

woozy (2)

grub (11606) | more than 2 years ago | (#37531536)


We have MRIs at work, I get that Just-Stepped-Off-A-Roller-Coaster dizziness when moving through the field, the effect is well known.

Old news or am I missing something?

Re:woozy (3, Insightful)

nedlohs (1335013) | more than 2 years ago | (#37531648)

Knowing it happens isn't the same as knowing the mechanism behind why it happens.

Re:woozy (1)

grub (11606) | more than 2 years ago | (#37531670)

One of the researchers here called it Vestibular [forget the word]. I googled it and there it was.

Re:woozy (0)

hedwards (940851) | more than 2 years ago | (#37532128)

That's probably vestigial. Which is basically just a way of saying that they don't know if it's useful any longer. People say the same thing about the ability to wiggle ones ears, even though it serves precisely the same purpose as it does in animals.

Re:woozy (1)

siride (974284) | more than 2 years ago | (#37532392)

No, he meant vestibular (having to do with the various balance systems in the head) and it's definitely *not* vestigial.

Re:woozy (0)

Anonymous Coward | more than 2 years ago | (#37533842)

I disagree, there's nothing about the endolymph or any of the other components which benefits from being thrown askew when exposed to magnetic fields. In the past that sort of sensitive might have been useful, but in this day and age it's increasingly problematic. At very least it wasn't harmful and now it is increasingly problematic.

So, saying it's definitely not related is a bit of a stretch.

Re:woozy (1)

tibit (1762298) | more than 2 years ago | (#37534366)

It's merely a byproduct of how semicircular canals work. We need them, without them our vision would be shot (never mind the balance!). It just so happens that they have ionic currents flowing across the channels. You need several Teslas to show the effect. There's nothing vestigial about it -- there was never a natural magnetic field that strong anywhere near animals with labyrinths in inner ear.

Re:woozy (1)

sjames (1099) | more than 2 years ago | (#37532522)

No, it probably isn't. We're pretty sure we still use our Vestibular system (our sense of balance).

Re:woozy (1)

grub (11606) | more than 2 years ago | (#37538766)

Quote from the researcher I mentioned in email, emphasis mine.:

Yes there is definitely a <b>vestibular</b> response that many people get when they move in and out of the magnet.

I trust her PhD... :)

Re:woozy (2)

cwebster (100824) | more than 2 years ago | (#37531942)

I'd say the effect is known. What may be new is that the fluid is ionic and interacts with a magnetic field. You can induce the same effects in an airplane, where its pretty easy to apply accelerations to your body that your ears (vestibular system) will interpret one way and your eyes in another way. Vertigo.

Re:woozy (2)

tibit (1762298) | more than 2 years ago | (#37534374)

Fluid being ionic is one thing, but there are actually ionic currents, and that's what the dealbreaker. And they must flow perpendicular to the pipe holding the fluid (the semicircular canal). It's an interesting confluence of things.

They need an MRI ear deGausser (0)

Anonymous Coward | more than 2 years ago | (#37532078)

Never thought I'd put those words together like that.

Re:woozy (1)

DeadCatX2 (950953) | more than 2 years ago | (#37532368)

I think everyone knew that physically moving through the magnetic field can cause physiological responses. What surprised me is that even for a stationary subject, there's a physiological response.

Unfortunately, the article is VERY light on details. It doesn't even say how strong the scanners were. Can they recognize this effect in a 1.5T? In a 3T? I would certainly believe as you get up to 7T that some strange shit can happen.

Re:woozy (1)

iroll (717924) | more than 2 years ago | (#37533092)

What's the difference between physically moving through a magnetic field and a stationary object experiencing a moving magnetic field?

(spoiler alert: there isn't any)

Re:woozy (1)

DeadCatX2 (950953) | more than 2 years ago | (#37533234)

I won't argue with you on that point.

However, the primary magnetic field in an MRI does not move. In fact, it must be as uniform as possible, and shims are used to make sure that the field homogenous.

The gradients change the field, but by orders of magnitude less than the primary field.

Re:woozy (1)

ColdWetDog (752185) | more than 2 years ago | (#37533328)

TFA doesn't give real numbers, but it stated that the newer (more powerful) MRIs tended to cause more problems than "old" ones.

Re:woozy (1)

iroll (717924) | more than 2 years ago | (#37533358)

Ok, so the field is uniform in orientation and magnitude spacially, but not uniform in magnitude temporally. You're "sitting still in a uniform field" that's changing in magnitude... which is going to induce eddy currents in a conducting fluid, which you're full of =)

And it had better be changing in magnitude, or else we wouldn't get Magnetic Resonance Imaging out of it!

The physics of this is all very high school; it's the physiology that's interesting to me.

perception? (1)

way2trivial (601132) | more than 2 years ago | (#37537954)

as in- subject perception?

imagine you have the ability to increase and decrease gravity localized to me by 1 percent.

if I'm lying down, and you range gravity from .99 to 1.01 of normal, I may notice something weird.
if I'm doing a straight bike riding on a bumpy road I may not.

on a trampoline, it may well depend on how you time the changes, but I may never notice.

Re:woozy (0)

Anonymous Coward | more than 2 years ago | (#37537950)

Even at 7T things are pretty tame. If I move my head back and forth in the fringe field I can feel a bit woozy for a moment but after a second or so it passes. However the effect is so slight that I usually don't bother waiting; I just keep working at a normal pace and smile a bit when I notice the slight effect of the fringe field.

I guess it would be similar with pilots of small aircraft. If you hit an air pocket and the plane lurches a passenger may feel momentarily disoriented but the pilot just smiles a little. Everything is fine, just keep on going.

Weird (0)

Anonymous Coward | more than 2 years ago | (#37531556)

I thought magnetic fields had no effect on living tissue? This is the standard response from the laughably narrow-minded biologists and the equably hilarious pseudo-educated engineers.

Re:Weird (2)

Anonymous Coward | more than 2 years ago | (#37531612)

Fucking magnets - how do they work?

Re:Weird (0)

Anonymous Coward | more than 2 years ago | (#37533850)

The only reason I clicked on this was to see if it would have the ICP reference.....You have made me happy.

Re:Weird (0)

Anonymous Coward | more than 2 years ago | (#37533990)

Dunno, I never fucked a magnet.

Re:Weird (1)

nedlohs (1335013) | more than 2 years ago | (#37531666)

The fluid in your inner ear is not "living tissue". So you miss again.

Re:Weird (0)

Anonymous Coward | more than 2 years ago | (#37532244)

The fluid in your inner ear is not "living tissue". So you miss again.

So what exactly qualifies as living tissue then? Your body makes plasma (analogous to inner ear fluid) which is an integral part of your cardiovascular system. Is "living tissue" simply the sum total of our self-replicating cells? Or is it everything those cells use to and produce? Would include your bones or just the marrow? Red blood cells but not plasma? Muscles but not tendons?

I would suggest that living tissue is the whole organism - including any clever use of non-self-replicating parts like bones or blood plasma or...ear canal fluid.

Re:Weird (1)

zoloto (586738) | more than 2 years ago | (#37532664)

No. Don't confuse the issue with the infinite loop of logic. It effects a liquid. Plain and simple. How the surrounding tissue and brain uses that liquid to interpret visuals is entirely irrelevant.

Re:Weird (1)

innerweb (721995) | more than 2 years ago | (#37532936)

So, water is a living tissue?

Re:Weird (0)

Anonymous Coward | more than 2 years ago | (#37533876)

Sure. Do you think you are a separate entity from the rest of this planet? Water in a cell, is it alive? What if I just exhaled that molecule? Is it dead now? If just drank one, is it alive now? Alive is a pattern. Is a bit considered part of a word processor or of a game? Doesn't matter, one day it's one thing, then it's another. It all depends on the other bits around it, their organization. Do you think a magnetic field only affects water water, or water in a cell, or in a canal? You're just showing your blissful narrow-mindedness, to not stray from the path of your BSc.

Re:Weird (0)

Anonymous Coward | more than 2 years ago | (#37535382)

What the fuck are you babbling about? H2O is not alive unless you're talking about organisms contained in a particular sample. No amount of hippie Gaia nonsense is going to change that.

Re:Weird (1)

slackbheep (1420367) | more than 2 years ago | (#37537866)

Oh god I was waiting for one of these guys to show up.
" We're all a part of the Earth Mother, man. I'm like connected to all life when I breathe So you see it's like the same thing all over man, We're all just breathin'. "

Re:Weird (1)

Kratisto (1080113) | more than 2 years ago | (#37531688)

Nope. There's even some cool experiments involving magnetic manipulation of the brain. Check out the God Helmet [wikipedia.org] (of course, there's some controversy over this one and it looks like sketchy science, but I think it still demonstrates that EM fields can have biological effects).

Re:Weird (0)

Anonymous Coward | more than 2 years ago | (#37531742)

I'm an engineer, and I admit that magnetic fields have effects on living tissue. I even know some biologists who would admit the same. I haven't heard of much evidence that powerful static fields cause permanent biological damage, but I am still wary about working around them. Also, I don't know what 'equably' means--can you help me out there?

Re:Weird (0)

Anonymous Coward | more than 2 years ago | (#37531894)

Living tissue is made of matter.
Matter is subject to the laws of physics.

Re:Weird (1)

Kilrah_il (1692978) | more than 2 years ago | (#37532780)

Wood is matter. Does wood react to magnetic fields? Just because the body is made from matter, does not mean that anything can affect it.
Just to be clear, I do not say that magnetic fields do not affect the ear, I'm just saying that the fact that the body is matter does not mean it automatically does.

Re:Weird (0)

Anonymous Coward | more than 2 years ago | (#37533252)

With a strong enough magnetic field, yes.

Re:Weird (1)

Chris Burke (6130) | more than 2 years ago | (#37531932)

I thought magnetic fields had no effect on living tissue?

Magnetic fields don't have the effects you and the horseshit magnetic healing bracelets and EM-"sensitives" claim it has.

It might be easy to mistake that for "no effect under any circumstance" when you're already not worrying about reality.

Re:Weird (1)

hedwards (940851) | more than 2 years ago | (#37532196)

In this situation given that it's known that powerful magnets can impact the brain, it's quite telling that you seem to know at precisely what power that no longer is a concern. http://en.wikipedia.org/wiki/Magnetic_seizure_therapy [wikipedia.org]

But, of course it's obviously bullshit because everybody is equally sensitive to everything else.

Re:Weird (2)

Chris Burke (6130) | more than 2 years ago | (#37532438)

It's telling you use the bullshit argument of not knowing "precisely" where sensitivity ends when we're talking about effects that are orders of magnitude apart.

Of course I'll happily change my tune when someone can demonstrate a measurable effect on the body from a magnetic bracelet (why not headbands since it's the brain that is known to be affected?), or sensitivity to a Wi-fi router or cell phone tower in a double-blind study. So far such studies have shown no effect, ergo its bullshit.

But you're right -- surely not everyone is equally sensitive. Maybe by some coincidence everyone who thinks they're more sensitive turns actually turns out to be less sensitive!

Re:Weird (1)

hedwards (940851) | more than 2 years ago | (#37533954)

There is a burden of proof on those that have it to prove it from a technical stand point. However your conclusion that because there isn't a lot of supporting evidence that it's automatically bullshit isn't really the way that it works either.

There's plenty of things that are only recently being uncovered to suggest that those of us that have a very real and very consistent negative reaction to things like a wall of TVs is patently absurd though. If you've got 12 TVs on a wall, that's not a small amount of radiation to be dealing with. Especially if those particular devices are of low quality and poorly shielded. Personally, I'm satisfied that the effect is real from the years where I could consistently identify which TVs were on and which were off based upon which ones gave me a head ache.

I do concede that it's unlikely to the max that a small magnet is going to have much of an impact, if any, on ones health. The sorts and amounts of radiation that people are being subjected to on a daily basis hasn't adequately been studied to know precisely where the limits might be for sensitivity.

Re:Weird (1)

Anonymous Coward | more than 2 years ago | (#37532110)

If magnetic fields had no effect on living tissue, MRI's wouldn't work. The biologists and engineers you speak of are saying magnetic fields don't have permanent negative effects. This is about as permanent as spinning around in a chair for 10 seconds and getting dizzy.

Re:Weird (2)

DeadCatX2 (950953) | more than 2 years ago | (#37532212)

You're fucking stupid and you can't type, either (equably, lol).

Biologists and engineers know that sufficiently large magnetic fields can affect living tissue. There are YouTube videos of living frogs levitating inside a 10T bore.

Biologists and engineers ALSO acknowledge that RF has an effect on living tissue. This effect is otherwise known as "heat".

Re:Weird (-1)

Anonymous Coward | more than 2 years ago | (#37534240)

So... Alllllll frequencies from 1mHz to >THz are allllllll "heat" to living tissue? Tell me, does it hurt to be so blinkered? Do you walk into walls often? Oh, and I was typing in a 10T field, you insensitive clod.

I'd rather make typos that blatantly false assertions like "Consider that infrared rangefinders with a range of a few feet measure the latency between the transmission of an IR pulse and the return of its reflection." which a moment's thought would have shown makes little to no sense at. And I'm fucking stupid?

Autistic, smug, self-satisfied and narrow-minded electrical engineer detected!!!

Re:Weird (1)

ceoyoyo (59147) | more than 2 years ago | (#37535168)

STATIC magnetic fields don't have much effect on tissue. Changing magnetic fields have an effect on anything that conducts electricity, living tissue included. The effects are well known and the rate at which the magnetic fields in an MRI scanner can change is regulated to avoid causing unwanted nerve stimulation.

You might want to be a little more careful before calling a trained professional narrow-minded or pseudo-educated. Unfortunately your post is the one that comes across that way.

This is not new (1)

lurker1997 (2005954) | more than 2 years ago | (#37531602)

Anyone who works around MRI magnets has known this for years. When I was a graduate student, you would always hear stories about people moving their hear around the end of the magnet (where the field gradient is highest) and making themselves dizzy.

Re:This is not new (2)

pz (113803) | more than 2 years ago | (#37531816)

I did this just the other day! It's actually a bit scary because if you are just working with the magnets (and not a subject), then it only happens with high field systems. You know, the ones that can accelerate a forgotten pen or a paper clip into a lethal weapon. And it happens just when you're leaning your head over the entrance to the magnet, making an adjustment, and likely to be doing something stupid. It was scary the first time it happened to me, and it still gives me serious pause when I approach the barrel.

Re:This is not new (3, Interesting)

tibit (1762298) | more than 2 years ago | (#37534478)

Do not close your eyes, and keep plenty of illumination (the more the better). This can at least inhibit the nystagmus to some extent. So at least you won't lose your visual acuity. The extra scary part, when talking about paperclips and such small things, is that inappropriate nystagmus (such as in a large magnetic field) causes you to lose visual sensitivity to high spatial frequencies, and paradoxically increases sensitivity to low spatial frequencies. You stop seeing small stuff, and you can remain unaware of it. The brain will, for a while, substitute made-up stuff to match your expectations. This is what gets fighter pilots killed: they get G-force induced nystagmus, lose acuity needed to read the instruments, and their brain is substituting expected (but incorrect) values for real instrument readings...

Re:This is not new (1)

PopeRatzo (965947) | more than 2 years ago | (#37531924)

Anyone who works around MRI magnets has known this for years.

Chinese medicine has long emphasized the reaction of the otolithic structures that provide the brain with the ability to sense roll, pitch and yaw in regard to the position and movement of the head to magnetic fields. Why would we think that the structures of sense should only be affected by only very specific and arbitrary portions of the spectrum?

We have somewhere between 9 and 21 different senses (a sense being defined as the physiological capacity of specific structures within the body (mostly in or near the brain) to perceive some (mostly physical) phenomena. It's not surprising that magnetic energy would affect one (or some) of them. Gravity affects many of them, so why not magnetic energy?

Re:This is not new (2)

Cyberax (705495) | more than 2 years ago | (#37532134)

On what magnetic fields? MRI fields are _tremendous_, you won't be able to sense anything with simple hand-held magnets, even with the rare-earth ones.

Re:This is not new (0)

Anonymous Coward | more than 2 years ago | (#37532892)

Indeed. I wonder if most people realize that MRI is done using Superconducting coils? And that the Big Red Button actually flushes the coolant to manage the emergency magnetic field quench (and causes a big maintenance bill to replace the coolant and check that nothing got damaged in the process)...

1T is the average strength of the Earth's magnetic field. Being inside a 7T field is just absurd as far as human nature goes, you CANNOT find it in this planet, anywhere human beings could possibly go. Even 1.5T is impossible to happen in nature (on Earth). You do require very specific and awesome machines to do that :-p and it is no wonder your body will get out-of-wack when subject to such strong fields (and field gradients, which are actually more likely to cause issues to the body). It will interfere with any ionic flows as well, hopefully not enough to cause any non-negligible effects.

That isn't to say that small magnetic fiends cannot have biological effects, but they will be very very localized, for example, activate a small cluster of neurons near the skin where the magnet is pressed or something equally small.

Re:This is not new (1)

ByteSlicer (735276) | more than 2 years ago | (#37533868)

1T is the average strength of the Earth's magnetic field

That's incorrect. The Earth's magnetic field is at most about 60 microTelsa.
1T is an enormously strong field, see here [wikipedia.org].

Re:This is not new (0)

Anonymous Coward | more than 2 years ago | (#37532646)

Because there's no such thing as magnetic energy. There is a magnetic potential, and magnetic potential energy, as well as a gravitational potential and a gravitational potential energy, but no "magnetic energy". Thank you come again.

Re:This is not new (1)

tibit (1762298) | more than 2 years ago | (#37534488)

The chinese medicine is bullshit in that regard. There are no natural magnetic fields anywhere on Earth that are big enough to cause this effect.

Re:This is not new (1)

tibit (1762298) | more than 2 years ago | (#37534464)

The original article in Current Biology (abstract free, rest behind paywall) clearly says that gradients are irrelevant. It's a Lorentz force, for that you simply need a large static field. Moving your head probably exaggerates the effect because there's a mismatch between vestibular input and visual and proprioception inputs. What's important is that for the first time they had clearly shown that it's a Lorentz force, causing a pressure signal to be applied to the cupola in the semicircular canal. Nobody else has conclusively shown that before.

Re:This is not new (1)

ceoyoyo (59147) | more than 2 years ago | (#37535372)

The Lorentz force is f=q[E + (v x B)]. That is, if you've only got a magnetic field you need some v in order to get some f. The charge has to be moving in relation to the field. In the paper they use a form of the equation with current instead of a moving charge, but it's the same thing.

They DO test in a static field, and see an effect, which suggests that there is a continuous current in the semicircular canals (which seems weird). A changing field (due to head movement or gradients) would certainly increase the effect though, and might well be much stronger, particularly in the case of quickly changing gradients.

Now we know that EMF causes this. (1)

Anonymous Coward | more than 2 years ago | (#37531636)

Radio Wave Propogation too.

Outside of EMF and RF, scar tissue and acidosis is the verry location where most cancer forms. This would explain why Cell Phones and other phenomenons are LINKED to cancer but they don't cause cancer but simply impede the Immune System long enough that a culture of pathogen can increase it's generations to adapt and grow into the body while the Immune System is dysfunctional.

Re:Now we know that EMF causes this. (3, Funny)

YodasEvilTwin (2014446) | more than 2 years ago | (#37531818)

Congratulations, you know absolutely nothing about cancer or biology in general.

Re:Now we know that EMF causes this. (1)

vlm (69642) | more than 2 years ago | (#37531968)

Congratulations, you know absolutely nothing about cancer or biology in general.

Don't overestimate the physics displayed either... there is a huge difference between slowly moving thru an intense static magnetic field and an electromagnetic wave.

I suppose when anything technological is magic, all you have to guide yourself is fear...

I started this thread, why do you guys do this? (0)

Anonymous Coward | more than 2 years ago | (#37533770)

I got this information from http://cancerisafungus.com/ [cancerisafungus.com] by a reputable surgeon.

There is also the matter of Dr Warburg's Nobel Prize for his achievement of determining that Cancer and Fungus are linked by the host's bodily substrate PH become acid.

Yet the first response I get is claiming I know nothing about biology? Explain how Pharmaceutical companies kill 4 million per year from resulting infections of surgeries, and over 500 doctors suicide each year from suicidal depression because they can't cure anything? Maybe it's because you want to die, and all you ever learned was in Doctrine form of a University lab not in the field with your own credibility on the line. That's the problem with certifications, is you blame your credentials as being wrong rather than yourself being liable for your fuckups.

Re:I started this thread, why do you guys do this? (1)

Weaselmancer (533834) | more than 2 years ago | (#37535128)

It's on the internet - it must be true!

BTW everyone - the link AC posted is to a guy who is trying to cure cancer with baking powder because he thinks it's a fungus.

Re:I started this thread, why do you guys do this? (1)

Xacid (560407) | more than 2 years ago | (#37535454)

Well we have come up with some other fairly crazy treatments that were successful. Hell - penicillin is a decent example. Let's treat infections with mold. On the surface - sure it sounds wacky.

Not that I'm outright supporting this guy's claim but just because it sounds odd doesn't mean it must be false.

You read wrong. It's Sodium Bicarbonate. (0)

Anonymous Coward | more than 2 years ago | (#37536048)

Your lack of precision astounds me. It is Sodium Carbonate (without Aluminium) annealed to Maple Syrup, so don't play stupid.

It's fucktards like you that give the practice a bad reputation, and your unjustified fear of competition is discerned in the voracity of your unfounded criticism.

Somone either presents a hypothesis, has field trials, collaborates with fellows of same character, and improves their commerce, or they get a bad reputation and bad statistic like Abbot Laboratories and Merck and Pfizer.

Re:I started this thread, why do you guys do this? (1)

ceoyoyo (59147) | more than 2 years ago | (#37535386)

Congratulations. Your creativity is stunning. If you'd turn it to a useful pursuit instead of making up crap to troll Slashdot....

I didn't make this up. (0)

Anonymous Coward | more than 2 years ago | (#37536646)

All my sources are verifiable.

The truth is funnier than fiction, and the astroturfing you people are doing to my commentary.

Re:I started this thread, why do you guys do this? (1)

evilviper (135110) | more than 2 years ago | (#37536992)

No, he's not a reputiible surgeon, he had his license to practice medicine taken away because his insane treatments were killing people.

See the following link for some real facts:

  http://scienceblogs.com/insolence/2008/08/a_fungus_among_us_in_oncology.php [scienceblogs.com]

And I have no idea what you're talking about wrt Dr Warburg's cancer research. PH balance has notging to do with it. "the prime cause of cancer is the replacement of the respiration of oxygen in normal body cells by a fermentation of sugar." -- Dr. Otto H. Warburg in Lecture

Re:Now we know that EMF causes this. (3, Funny)

N0Man74 (1620447) | more than 2 years ago | (#37531872)

Forget magnets....

Fucking cancer, how does it work?

Re:Now we know that EMF causes this. (0)

Anonymous Coward | more than 2 years ago | (#37533830)

ICP FTW

Re:Now we know that EMF causes this. (1)

poetmatt (793785) | more than 2 years ago | (#37532190)

This is about as accurate in terms of "cell phone cancer" as comparing your ability to sense a volcano's heat from dipping your toe in the lava versus the ability to test the ambient air temperature being 1/3 of a degree higher or lower than your body temperature in a room without wind.

One is painstakingly obvious, the other will basically never happen. That's how big of a different these MRI magnets are.

This explains it... (2)

ackthpt (218170) | more than 2 years ago | (#37531758)

The rapid eye movement, looking from side to side, peeking under things, etc. while out geocaching near guardrails.

RTA (2)

nikolag (467418) | more than 2 years ago | (#37531846)

This is a classical example of how you just have to take the time to read the paper and think about it because the cited text and other sources that are not behind pay-wall are just not clear enough.

I have had put my head in number of MR scanners, with field strengths of 0.3T, 0.5T, 1T, 1.5T, 2T, 3T, and 7T, with no nistagmus, but that simply does not mean anything in context of this paper.

You should have in mind that the maximum magnetic field gradients, and their speed are regulated by law.
Interesting question that this paper is offering: are functional-MRI results sometimes tainted by effects of magnetic field gradient while the person is placed inside the device?

Re:RTA (1)

DeadCatX2 (950953) | more than 2 years ago | (#37532490)

I agree with most of your post. I've been in a scanner a few times, and I knew a guy who has had probably in excess of 100 hours being scanned. I also know a lot of people that regularly go into the magnet room. The only issue anyone has ever had involved moving their head rapidly through the field.

I disagree with fMRI point, though. An fMRI usually involves a control task (e.g. read these words but don't talk), and an experiment task (e.g. read these words and say them aloud). Then the images collected are analyzed for differences, and those differences would represent areas of the brain involved in e.g. speech. Any nystagmus effect would be present in both images, and would therefore be canceled out.

Re:RTA (1)

SirLoadALot (991302) | more than 2 years ago | (#37534104)

As long as you control for the vestibular response of your subjects -- or have enough to drown the effect out. Having vestibular issues isn't all that uncommon -- my daughter has been seeing an occupational therapist for just that.

Re:RTA (1)

tibit (1762298) | more than 2 years ago | (#37534522)

Try it with your eyes closed, in a darkened room :) Some people are better than others at suppressing nystagmus when there's something to look at.

The effect does not care about gradients, just about a static field. Most people are blissfully unaware of having nystagmus, you'd have to train yourself to recognize it. Our visual system will lie to you when you have nystagmus and you'll feel like you don't have it.

Re:RTA (1)

ceoyoyo (59147) | more than 2 years ago | (#37535398)

Unfortunately reading the paper itself doesn't immediately make things much clearer. These guys should learn about the "Methods" section.

Is this correct? (0)

Anonymous Coward | more than 2 years ago | (#37531926)

I don't doubt the dizziness, but the explanation. The fluid gets moved around because of the current?

Electrical currents in the body are extremely weak. They would not cause heavy fluid to move and excert pressure. If the magnet really can do that, then you'd also feel considerable force due to the nerve impulses in the body - and in the brain. Surely that might cause even more dizziness...

Re:Is this correct? (1)

tibit (1762298) | more than 2 years ago | (#37534554)

The fluid doesn't get moved much, just pushed a little bit -- it's a semicircular canal after all, not a full torus. The pressures sensed by the cupola are on the order of probably nanopascals. This is nowhere near a "considerable" force.

Re:Is this correct? (1)

fbjon (692006) | more than 2 years ago | (#37537354)

The magnet in question is a MRI magnet, the word "weak" simply does not apply.

This sounds like an awesome new method of torture (0)

Anonymous Coward | more than 2 years ago | (#37532012)

I'm sure that the U.S. government is all over this already.

Many MRIs but no wooziness (1)

rbanzai (596355) | more than 2 years ago | (#37532198)

I have BPPV so I get dizzy pretty easily but after at least twenty MRIs I've never felt anything other than claustrophobia. I wonder if you have to go in head first to get the effect.

Re:Many MRIs but no wooziness (0)

Anonymous Coward | more than 2 years ago | (#37532270)

I've had quite a few MRIs neck and shoulders the last year, so head first and head in - not a single episode of anything other than boredom. On the plus side, the scanner sounds pretty much like the music I like to listen to anyway.

I still think someone should consider pasting autostereograms to the inside roof.

Re:Many MRIs but no wooziness (1)

DeadCatX2 (950953) | more than 2 years ago | (#37532526)

Many sites these days have projectors that allow a subject in the scanner to see an image. It can help distract from claustrophobia.

Re:Many MRIs but no wooziness (1)

Dachannien (617929) | more than 2 years ago | (#37532946)

BPPV is frequently caused by solid matter (calcium crystals) in the semicircular canals coming loose, floating around, and moving the fluid in abnormal ways to cause stimulation and therefore vertigo. Wikipedia has a good article on the subject [wikipedia.org] and provides descriptions of two head-positioning techniques that you can do by yourself at home to help the solid matter settle back to where it will (at least temporarily) stop causing problems.

Good summary! (2)

History's Coming To (1059484) | more than 2 years ago | (#37532856)

A quick note to tibit, the submitter, to say nice summary. No hyperbole, no outrageous barely marginable links to another agenda, a suggestion, mechanism and evidence. I really enjoyed it, a bit of my brain went "Really? Oh? Like that? Oh that's quite clever, I see what happened there."

You know, it actually makes me want to go and read the article. I think I will. Nice one. More weirdly interesting stuff like this please. Off-topic in many ways, sorry. If it makes up for it, I learned to look for nystagmus when working as a bartender. There's a fairly strong correlation between BAC and the degree of nystagmus in a drunk person as they follow an object with their eyes. You can use this to judge how drunk a person is fairly accurately. In the "controlled circumstances" of me asking off-duty colleagues and friends to follow a finger for ten seconds I could usually work out how much they'd had to drink to the nearest 10ml of alcohol (1/2 pint or a shot of whisky in the UK).

First time submitter... (0)

Anonymous Coward | more than 2 years ago | (#37532888)

Fire whatever marketing drone came up with the idea that first-time submitters need to be recognized. Its fucking annoying, stop it.

Finally someone demonstrates this! (1)

Vellmont (569020) | more than 2 years ago | (#37533044)

Years ago I participated in a paid research study as part of the control group. Part of the research was having an MRI done. After being in the MRI for a short period of time I had the oddest sense of vertigo, despite staying perfectly still. I asked the technician about this, and he brushed it off like it didn't happen, or I imagined it. I was sure he was just wrong, and went home and did my own research. I recall finding some people who had the same experience, but no real idea what the mechanism was. It's fascinating that years later, I have an explanation of what I felt dizzy in the MRI. (Interestinginly, it seemed to persist for a half hour after leaving the MRI).

temporarily cause (1)

kc8tbe (772879) | more than 2 years ago | (#37533100)

To clarify, giant magnets can temporarily induce nystagmus if you move around too quickly in their magnetic field. The nystagmus goes away when you leave. MRI machines cause nystagmus like wearing your winter coat in a sauna causes a fever.

Opti-grab (0)

Anonymous Coward | more than 2 years ago | (#37533662)

Didn't Steve Martin prove this in the Jerk with the invention of the Opti-Grab?

Grammar, people! (0)

Anonymous Coward | more than 2 years ago | (#37534360)

"The subject is laying down" - gack! Try "The subject is lying down" instead.

Is there a weapon here for riot control or hunting (1)

aurizon (122550) | more than 2 years ago | (#37535442)

Hit them with the field, and they will fall over (and all their metal objects, teeth, fillings, etc, will get hot or go flying)

Re:Is there a weapon here for riot control or hunt (0)

Anonymous Coward | more than 2 years ago | (#37536364)

wtf is wrong with you?
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