OK, this behavioral study (
Prato et. al. 2013 ) which shows an extremely robust effect, deals with hyper-weak (33 nT) 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 box. The study sort of falls outside of the usual Magnetoreception studies to do with animal navigation. I only stumbled across it yesterday. It's one of the most thorough studies I've ever read, but I still don't know what to make of it. 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...
Over 5 days, separate groups of mice were individually placed on a hot plate to cause pain to their feet (
pre-exposure - open circles fig 2), and the length of time in seconds was recorded before they lifted a foot to lick it (latency). Immediately following foot shock, these groups of mice were placed inside various light shielded boxes, (
because photons somehow alter the observed analgesic effect)...
From left to right... they were individually placed for 1 hour inside a sham control fibreglass box (not expected to affect EM fields), a steel box (expected to reduce EF, but not MF), a mu-Metal box (expected to substantially reduce both EF
and MF), and a series of other identical mu-Metal boxes which had been fitted with coils that could produce the targeted MF's shown in figure 2.
Immediately following release from the box, the mice were again individually placed on a hot plate to cause pain to their feet (
post-exposure - filled circles fig 2), and the length of time in seconds was recorded before they lifted a foot to lick it (latency).
View attachment 769
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 box for 1 hour, had increasing latency to footshock after they left the box and were tested again. This behavior was in the opposite direction to groups of mice placed in the sham fibreglass, and stainless steel control boxes for 1 hour, as they had reduced latency to footshock after they left their box and were tested again.
By adding other mu-Metal boxes fitted with coils that could produce specific MF's, the authors now bizzarely show that these specific MF strengths and frequencies also allow an increasing latency in mice to footshock after they left their box and were tested again... however this time the effect only becomes visible on day 4 and 5, and is reduced by some 60%...
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 further each day). And that this effect is inversely related to what one would normally expect to see. But really bizzarely, this inverse reinforcing effect only appears on post-exposure, and not on pre-exposure to the mu-Metal box over the 5 days. Before the mice go into the mu-Metal box, 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!
...that hyper-weak magnetic fields in the frequencies shown, reduce (but not eliminate) this effect, makes things even more complicated.
At 33 nT, these fields are really too weak to have any known chemical effect, that could partially reverse the analgesic effect the authors describe.