Can hyper-weak magnetic fields affect behaviour… and memory?

Apparently so… this behavioral study ( Prato et. al. 2013 ) which shows an extremely robust effect, deals with hyper-weak (33 nanoTelsla) magnetic field (MF) effects on mice. These hyper-weak magnetic fields reduce a strange analgesic effect on mice previously discovered by the authors. This analgesic effect is caused by 1 hour of shielding from ambient MF’s inside a Mu Metal chamber. The study sort of falls outside of the usual Magnetoreception studies to do with animal navigation. It’s one of the most thorough studies I’ve ever read. It’s very detailed and somewhat difficult to understand so I will try to simplify, and briefly explain the main issues as I see it…

In fig. 1 below which took place over 5 days of experiments, separate groups of mice were individually placed on a hot plate to cause pain to their feet (pre-exposure – black circles), and the length of time in seconds was recorded before they lifted a foot to lick it. This lifting and licking behaviour  from a heated plate called ‘foot shock’, is generally accepted as a good indication of the degree of pain the mice are experiencing. Immediately following foot shock, these groups of mice were placed inside various light shielded chambers, (the light shielding is important because photons somehow alter the observed analgesic effect)…

From left to right… they were individually placed for 1 hour inside a sham control fibreglass chamber (not expected to affect electromagnetic fields), a stainless steel chamber (which is expected to reduce the electric component of any external electromagnetic field, but not the magnetic component – which should pass right through the steel), a mu-Metal chamber (expected to substantially reduce both the electric and magnetic components of any external electromagnetic field), and a series of other identical mu-Metal chambers which had been fitted with shielded EM coils that could produce hyperweak magnetic fields of different frequencies on demand.

Immediately following release from the chamber, the mice were again individually placed on a hot plate to cause pain to their feet (post-exposure – red circles fig 1), and the length of time in seconds was recorded before they lifted a foot to lick it.

250 mice were tested in this double blinded study, which replicates an earlier study, by bizarrely showing that the group of mice which we’re shielded from the earths local geomagnetic field within the positive control mu-Metal chamber for 1 hour, had increasing latency to footshock after they left the chamber and were tested again. This behavior was in the opposite direction to groups of mice placed in the sham fibreglass, and stainless steel control chambers for 1 hour, these mice had reduced latency to footshock after they left their chamber and were tested on the hot plate again.

This is really interesting, because it shows that being temporarily removed from the earths magnetic field, causes some type of behavioral reinforcing effect (because footshock latency time increases each day as the experiment progresses). And that this effect is inversely related to what one would normally expect to see. But really bizarrely, this inverse reinforcing effect only appears on post-exposure, and not on pre-exposure to the mu-Metal chamber over the 5 days. Before the mice go into the mu-Metal chamber, this group of mice have a similar response to pre-exposure footshock as all the other mice, but a completely different reinforcing effect to post-exposure footshock… which gets stronger every day!

By adding other mu-Metal chambers fitted with coils that could produce specific magnetic fields, the authors now bizarrely show that these specific MF strengths and frequencies still allow an increasing latency in mice to footshock after they left their chamber and were tested again… but this time the effect only becomes clearly visible on day 4 and 5, and is reduced by some 60%…

…in summary, they show that just these specific hyper-weak magnetic fields introduced by the researchers through shielded coils can reduce (but not eliminate) the analgesic effect, which makes things even more complicated.

At just 33 nanoTesla, these magnetic fields are over 1000 times weaker than the earths geomagnetic field, and are really too weak to have any known chemical mechanism, that could partially reverse the analgesic effect the authors describe.

I’ve been looking around for other other papers which may help shed light on Prato’s study… I came across a paper in which the authors produce a very similar analgesic response using combat-related stimuli in combat-related posttraumatic stress disorder (PTSD) suffers….

Pitman et. al. (1990) “Naloxone-reversible analgesic response to combat-related stimuli in posttraumatic stress disorder. A pilot study.”

http://www.ncbi.nlm.nih.gov/pubmed/2350206

This PTSD study also seems to show a distinct memory effect, and the basic similarity between both this study and Prato’s mice study, suggests to me that the results produced in the mice study, might also be related to memory.

Just in case I’ve not made clear why these studies are similar… both studies use organisms which have been exposed to a traumatic event in the past… and then expose them to a recreation of the traumatic event in the present… where a period of time has elapsed between both events. Both the PTSD sufferers, and the magnetically shielded mice display an analgesic effect.

The mice study implicates very weak ambient geomagnetic fields as being the important factor, and I’m therefore speculating that ambient magnetic fields might be important to a memory consolidation, such that blocking the ambient magnetic fields produces a PTSD-like response within the mice, and a subsequent analgesic effect upon re-exposure to the stimuli – just like the authors show in this study of combant related PTSD sufferers.

In mice who were also shielded from the ambient geomagnetic field within a Mu-metal chamber, but had a 33nT hyper-weak magnetic field reintroduced from a magnetic coil within the mu-metal chambers (much much weaker than the earths ambient field), the subsequent PTSD-like response is much reduced.

This difference between the mice groups sham control test, Mu-metal/33nT field test, and the Mu-metal positive control test, suggest to me something like a logarithmic effect from ambient magnetic fields on memory encoding. This would mean that the stronger the ambient magnetic field is, the smaller the contributory effect it has on memory consolidation, so that the weaker the magnetic field the dis-proportionally larger effect they contribute to memory consolidation.

Now that’s nice… because it seems to tie up with something we generally see from magnetoreception studies… that the weaker fields seems to be having some effect… where as the stronger fields don’t… that is, the weaker the field, the greater the effect (disproportionately speaking).

It’s also worthwhile considering the exciting Landler study on the spontaneous alignment of snapping turtles exposed to hyper-weak magnetic fields (MF) between about 30 – 50 nanoTesla.

Landler et al 2015 “Spontaneous Magnetic Alignment by Yearling Snapping Turtles: Rapid Association of Radio Frequency Dependent Pattern of Magnetic Input with Novel Surroundings”

This replicates the behavioural effects of hyper-weak magnetic fields on goal-directed orientation, but more importantly this clever study seems to demonstrate that magnetic fields appears to play an important, and as yet poorly understood role, in encoding spatial information in the animal’s immediate surroundings.

The results from these recent studies seem to show that hyper-weak magnetic fields may play a completely unexpected and crucial role in memory processing and consolidation.

 

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One thought on “Can hyper-weak magnetic fields affect behaviour… and memory?

  1. Pingback: Requirement for Hypomagnetic field (Zero field) studies may apply to anomalous research? | Thinking Deeper

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