Cats are worshiped by Egyptians. Cats are blogged on Fridays. Even cat’s downfall is analyzed in feline pesematology. Nevertheless, in this part of terra firma, cats crossing your path is considered a bad omen.
You step out of the house on an important errand, and a cat crosses your path; you (are made to) promptly stop, turn around and get back into home. You wait for sufficient time inside your home, drinking a cup of water before some one elderly checks the road and prompts when everything is auspicious again for you to get back on the road.
The “reasons” for considering cat crossing your path as a bad omen are many, with new ones given on the spur everyday. Let me give here the “scientific” one given to me some years back. It goes like this: Cats sense magnetic fields and since they do, they should be magnetic or at least capable of influencing magnetic fields. So, when they cross in front of you, cats influence the local geomagnetic field, which in turn manifest as a bad omen for you. Of course, this “scientific reason” wasn’t meant to be believed, but was given to make me think “what if” and in the process, not mind actually doing what the elders of the family asked me to do, i.e the routine in the previous paragraph, when I cross path with a cat.
Flash-forward. There is a recent Physics Today article on Magnetoreception in animals by Sönke Johnsen and Kenneth J. Lohmann that states
the idea that animals can detect Earth’s magnetic field has traveled the path from ridicule to well-established fact in little more than one generation. Dozens of experiments have now shown that diverse animal species, ranging from bees to salamanders to sea turtles to birds, have internal compasses.
It has been observed that many animals possess means for detecting magnetic fields. The familiar one for us is perhaps the pigeon but even sharks and salamander possess magnetoreception. However, it is not yet clear how exactly animals sense the magnetic field. Finding this mechanism is a current research area of sensory biology.
Three mechanisms of sensing magnetic fields are proposed so far in animals. Electro-magnetic induction, ferri-magnetism and radical pair reactions that are influenced by magnetic fields. All three proposed mechanisms are capable of obtaining information from the weak geomagnetic field (varies between 30 to 60 microteslas). However, with the exception of magnetotactic bacteria, no mechanism has been conclusively established.
Sharks and rays possess magneto-induced electroreception. A conducting rod, when moved through a magnetic field is induced with a charge distribution, based on the Lorentz force. However, due to the weakness of the geomagnetic field, it requires a highly sensitive receptor for sensing the field. Sharks seem to possess such a receptor in the form of long canals filled with a high conducting jelly, with the canals beginning at tiny pores in the skin surface and ending at a depth at the ampullae made of cells that are capable of detecting very small voltage differences (~ 2 micro volts/meter).
[Image Source: Physics Today, March 2008, p.29, Magnetoreception in Animals]
With such a sensitive receptor - to quote from the above PT article
[..] magnetoreception using induction (for sharks) is theoretically possible. Depending on its compass direction, a shark or ray moving horizontally through the ocean at 1 m/s (about 2 miles per hour) could generate a voltage gradient at the receptor as high as 25 µV/m, well above the detection threshold.
There are several other complications and debates about electroreception serving as a means for magnetoreception in sharks, which I shall skip for the moment. They are all adequately explained in the above article.
However, barring pigeons and bacteria, it is yet to be established that such magnetoreception techniques are present in terrestrial animals. To quote from the PT article
[..] electromagnetic induction appears unlikely to be a widespread mechanism for magnetoreception because only elasmobranchs are known to have the extreme electrical sensitivity required. Most animals with electroreceptors have electric thresholds two to five orders of magnitude higher—too high for magnetoreception. For example, the electric fish Eigenmannia (glass knifefish), a relatively electrosensitive animal, would need to swim at 400 mph (nearly 180 m/s) to detect Earth’s field using induction.
So, to answer my doubt about cats and their magnetoreception or ability to influence the geomagnetic field, I would conclude they just can’t do it. Assuming that cats possess such electroreceptive organs (which is yet to be established) like sharks with similar electric thresholds (highly unlikely) and their 2 miles/hour travel speed, cats crossing my path should do so at about a meter per second.
That is, when they do cross in front of me, I would be unaware that they did.
Let me move on to another such pet in-house theory in this part of the world. That one should not sleep by keeping one’s head in the north side.
The “scientific reason” given for this (by one of the elders in my house) is that if you sleep with your head resting in north direction, the earth’s magnetic field will adversely affect the body and hence your health. At least, sleeping north-south is supposed to induce lots of nightmares. I have been prompted time and again to lay my bed east west.
I am skeptical of this pet-theory as I am yet to find conclusive evidence that humans are affected by magnetic fields, that too, as weak as that produced by our geo-magnetic field. The only testable proposition of the above pet-theory is subjective and concerns my health. The only tangible verification is nightmares, which I don’t get, irrespective of the direction I sleep. I do get dreams, but they happen irrespective of my sleep direction. The in-house explanation for this of course is that if I never sleep north-south, my health would have been even better than what it is now.
One can never win such arguments.
Anyway, just to seek an answer to my doubt let me conjecture this. If my nightmares are controlled by my sleep position, which in turn is supposed to be influenced by the geomagnetic field, then one could conjecture that somehow the geomagnetic field affects human brain activity. At first glance, this seems possible. After all, the neurons in the brain, when active, are electrical signals (charges) in motion. It is possible that such a moving charge is influenced by a magnetic field of spatially or temporally varying field strength.
So I explored for corroboration for this phenomenon. For instance, the recent Physics Today article [see reference 1 below] that I mentioned above, states that human tissue is found to be not influenced by magnetic fields. It says, this is one reason intuitive understanding or the medical literature on human senses doesn’t help much in detecting the mechanism for magneto-reception in humans and animals.
[...] humans do not appear to have the ability to sense magnetic fields. Whereas most nonhuman senses, such as polarization detection and UV vision, are relatively straightforward extensions of human abilities, magnetoreception is not.
Also, the geomagnetic field is very weak for easy detection as stated in the above article
[...] the weakness of the interaction between Earth’s field and the magnetic moments of electrons and atoms, roughly one five-millionth of the thermal energy kT at body temperature, makes it difficult to even suggest a feasible mechanism.
A further web search landed me with at least three different evidences that suggest human magnetic sense [follow the links in reference 2 below]. But let me discuss here the results from a recent peer reviewed research paper in Neuroscience journal [see reference 3 below].
The paper title “Evidence of a nonlinear human magnetic sense” itself intrigues us. The authors have done experiments with 17 humans subjected to a local magnetic field (2 Gauss, 60 Hz - a field strength comparable to that in the general environment) applied around their head. See the picture below for the schematic of the experiment, taken and reorganized from the paper. Schematic (a) shows the magnetic field application, while (b) shows the measurement of brain electrical activity.
By measuring the brain activity through electrodes kept at various location on the head (see (b) in picture above), the authors are able to show that magnetosensory evoked potentials (MEPs) in the brain or its activity in terms of electrical signals is altered (or affected) by the switch on and switch off of such a 2 G magnetic field. To quote from the lucidly written discussion section of the paper (even a non-expert like me can follow it easily)
[...] the observed changes in brain electrical activity were true MEPs. The results therefore can be interpreted to show that human subjects possess a magnetic sense. The mechanism of this sense as well as the anatomic location at which it is mediated (see below) remains unexplained. Further, transduction of the field (conversion into an electrical signal by a receptor) did not result in perception, as in the case of the special senses. Thus the “magnetic sense” must be understood more narrowly, similar to the chemical senses for detection of pH, O2, and blood pressure.
To put this finding in perspective, I quote one more paragraph from the discussion section in full (omitting the references)
Strong magnetic fields (
10,000 G), such as those used for transcutaneous magnetic stimulation, instantaneously activate voltage-sensitive ion channels in axonal membranes. Fields on the order of 1 G cannot do so, and their biophysical mechanism of action is still unknown. Nevertheless, they can produce electrophysiological changes in animals throughout the phylogenetic spectrum. In some species, specialized receptor organs have been described. The anatomical basis for the detection of weak fields by human beings, however, has not been located. Consequently, the best evidence presently possible that human beings possess a magnetic sense consists of measurements of potentials evoked by a field stimulus. The primary objective of this study was to provide direct evidence indicating that detection of weak fields was a form of sensory transduction.
Bold font-face is mine.
So let me speculate now - I am no expert in neuroscience - to answer my doubt about my sleep position.
Even if human brain activity could be influenced by a magnetic field, while sleeping, neuron activity of the brain is expected to be minimal - not a conducive situation for magnetoreceptive interaction leading to nightmares. Further, as the current scientific knowledge indicates, there is no conclusive proof that humans exhibit magneto-reception anywhere in their body (leave alone brain) to detect the weak geomagnetic field (weaker than what is tested in the experiment discussed above). Brain activity is evidenced only to be influenced by proximity external magnetic stimulus. So I don’t need to relate my nightmares - if I get them - to my sleep position.
My dreams and nightmares could after all have a simple explanation in what I ate that day. Wonder how what I eat can affect my dreams? Well that is another age old belief in this part of the world that needs exploration.
References
1. Sönke Johnsen and Kenneth J. Lohmann, Magnetoreception in animals, March 2008, page 29, Physics Today
2. Magnetoreception Wikipedia page [sites one two three webpages that discuss human and animal magnetic sense]
3. CARRUBBA, S., FRILOTII, C., CHESSONJR, A., MARINO, A. (2007). Evidence of a nonlinear human magnetic sense. Neuroscience, 144(1), 356-367. DOI: 10.1016/j.neuroscience.2006.08.068
