Those dudes shoving rare-earth magnets under their skin are basically feeling a magnet pulling against it. I don't know if that's true magnetosensation.
For the sake of playing devil's advocate, I'll argue it could be, especially if it generates a new passive perception of your environment. Even if the information is being fed to somatosensory receptors, the information conveyed and interpreted is still magnetic-field information at the end of day. The bigger question to me is: can you feed different information streams through shared receptors and be able to maintain two distinct senses out of this? In the case of the magnets in the finger-tips, it may not end up being too confounding as I would guess the push/pull of the magnets would be peristant and override other tactile information at those specific receptors. :: shrug :: I'm just playing thought-games, though.
There are a lot of different kinds of somatosensory receptors (touch, temperature, proprioception, nociception, introception), and it's hard to tell which receptor would be most suited to transducing a magnetic stimulus, much less if it truly does. I think, to be honest, we can't really know what the heck true magnetoception is until we grow some magnetite crystals in our noses.
So magnets act as an electromagnetic energy -> kinetic energy transducer, which is what certain somatosensory receptors are good at detecting (i.e. SA-II and Pacinian receptors).
I think the issue you raise is word/term-based. Does "magnetoception" mean you have perception of magnetic field information, independent of the sensory pathway? Or does it require the use of a sensory pathway that evolution produced specifically for that type of information? Does it have to be the same type of perception of EM-fields that other animals have? I imagine magnetoception is not consistent across different animals.
Implanting magnets in your finger-tips could be considered a "hack" for translating magnetic information to a domain that allows for non-magnetic (e.g. SAII/Pacinian) receptors to fire in a manner that is tightly correlated with a surrounding EM-field. In that regard, you are successfully transmitting magnetic information to the CNS (albeit in an atypical way), and the central point of debate is: is the brain capable of decoding that as a new perception, independent of what receptor/type of receptor sent that information up the system?
How is it different from bits of magnetite in a birds beak? If the brain is as plastic as Eagleman says, it's the closest thing we're likely to get for quite some time. Continuing that thread of thought, what would be true magnetosense? Genetically inducing magnetite accumulation in fingernails? Bones?
So I poked around the literature and it says (this is from 2013): The first thing that jumps out at me is that the trigeminal nerve (specifically the ophthalmic branch) and the trigeminal system in general mediate this. The trigeminal nerve handles both sensory and motor signals, and the histology doesn't seem to line up with touch receptors observed elsewhere in bird bodies. Wikipedia sez: The answer appears to be 'we have no fucking clue'. In cartilaginous fish, there are the ampullae of Lorenzini: Hens have mineral deposits in the dendrites in their beak, which is radically different from the usual touch receptor.Behavioral evidence indicates that there are magnetoreceptors in the beak of birds. These receptors include magnetite, as indicated by the pulse experiments, and they mediate their input to the brain by the ophthalmic nerve and the trigeminal system. They are not involved in the avian magnetic compass; instead, they seem to normally convey information on magnetic intensity. Their natural function appears to be to provide birds with magnetic information as one factor in the multi-factorial navigational ‘map’—not only homing pigeons within their home region, but also migrants when they return to their familiar breeding site or wintering area. The exact position of these magnetite-based receptors is unclear. The effect of the local anesthetic seemed to speak in favor of the receptors described in the skin of the upper beak (e.g., Hanzlik et al. 2000; Fleissner et al. 2003; Falkenberg et al. 2010), yet the histological study by Treiber et al. (2012) calls the existence of these receptors in question, a finding that received considerable public attention. This may point to the single-domain receptors described in the nasal region (e.g., Beason and Nichols 1984, Beason and Brennan 1986; Williams and Wild 2001), but it appears highly unlikely that the externally applied anesthetic could have reached them. The observation that young chickens with the tip of their beak removed, as routinely done in the poultry industry, were impaired in locating a magnetic anomaly (Freire et al. 2011) also suggests a position of the receptors further in front of the beak.
For animals the mechanism for magnetoception is unknown, but there exist two main hypotheses to explain the phenomenon.[4] According to one model, cryptochrome, when exposed to blue light, becomes activated to form a pair of two radicals (molecules with a single unpaired electron) where the spins of the two unpaired electrons are correlated. The surrounding magnetic field affects the kind of this correlation (parallel or anti-parallel), and this in turn affects the length of time cryptochrome stays in its activated state. Activation of cryptochrome may affect the light-sensitivity of retinal neurons, with the overall result that the bird can "see" the magnetic field.[5] The Earth's magnetic field is only 0.5 Gauss and so it is difficult to conceive of a mechanism by which such a field could lead to any chemical changes other than those affecting the weak magnetic fields between radical pairs.[6] Cryptochromes are therefore thought to be essential for the light-dependent ability of the fruit fly Drosophila melanogaster to sense magnetic fields.[7] The second proposed model for magnetoreception relies on Fe3O4, also referred to as iron (II, III) oxide or magnetite, a natural oxide with strong magnetism. Iron (II, III) oxide remains permanently magnetized when its length is larger than 50 nm and becomes magnetized when exposed to a magnetic field if its length is less than 50 nm.[8] In both of these situations the Earth's magnetic field leads to a transducible signal via a physical effect on this magnetically sensitive oxide.
These organs are made up of mucus-filled canals that connect from the skin's pores to small sacs within the animal's flesh that are also filled with mucus. The ampullae of Lorenzini are capable of detecting DC currents and have been proposed to be used in the sensing of the weak electric fields of prey and predators. These organs could also possibly sense magnetic fields, by means of Faraday's law.
I interviewed up at BCM this past year. Dave Eagleman is a cool dude.
Right on. For med school or neuro? Are you attending?
Neuro. Got rejected. Was told I would have gotten in had they got their training grant like they usually get this year.
Oh right, I should have assumed from your username. Sorry to hear that it didn't work out!