(ORDO NEWS) — Numerous organisms use the Earth‘s magnetic field as a sensory cue to migrate, align the body, or search for food.
It is believed that a person does not feel the geomagnetic field, but a new study has confirmed the existence of a human magnetic sense and suggested the presence of a quantum mechanical mechanism of magnetoreception.
The scientists behind the new study write that they figured out that the magnetic field is the mechanism that determines light-dependent magnetic orientation in men, using the swivel chair experiment combined with a two-choice forced choice method.
Two groups of subjects with different abilities for magnetic orientation were identified. The magnetic orientation of the subjects was sensitive to the wavelength of the incident light and was critically dependent on blue light entering the eyes.
It is important to note that, apparently, these reactions are due to the resonant mechanism of the magnetic field, as evidenced by the violation or enhancement of the ability to orientate by radio frequency magnetic fields at the Larmor frequency and the dependence of these effects on the angle between the radio frequency and geomagnetic fields.
In addition, the inversion of the vertical component of the geomagnetic field revealed a non-canonical effect of compass tilt on magnetic orientation. These results support the existence of the human magnetic sense and suggest a quantum mechanical mechanism for magnetoreception.
Numerous organisms from a wide range of taxa, including birds, sea turtles, reptiles, insects, magnetotactic bacteria, and plants, use the geomagnetic field (GMF) as a sensory cue for migration, short distance movement, body alignment, foraging, or growth (plants ), depending on the species and biological context.
Information about both the magnetic compass and the magnetic map can be obtained from the GMF; the first is necessary for various types of magnetically sensitive behavior.
The tilt compass or polarity compass can provide animals with directional information through contrast mechanisms: light dependent radical pairs in cryptochromic flavoproteins in bird eyes and light independent iron containing biogenic magnetite in bacteria or salmon ethmoid bone.
It is believed that light-induced radical pairs consisting of a flavin-adenine dinucleotide (FAD) radical and a tryptophan radical in cryptochromes act as a magnetic compass sensor in migratory birds through a quantum mechanical mechanism.
In these species, the tilt compass is activated by blue or green light24 and disturbed by red light, indicating that different wavelengths play different roles in radical pair-mediated behavior21.
Research on magnetoreception in humans is very limited. It is widely believed that the Earth’s static magnetic field is not perceived by humans, while alternating magnetic fields such as power frequency fields and pulsed fields can have negative health effects and therapeutic applications, respectively.
After previous conflicting reports, two recent studies using different experimental approaches support the existence of GMF responses in people with a sharp contrast.
In the swivel chair experiment, hungry men, but not women, were able to navigate based on blue light to a specific magnetic direction previously associated with food in the surrounding GMF31.
This study suggests that magnetoreceptors are in the eyes, but does not demonstrate an underlying sensory mechanism. On the contrary, electroencephalography has shown that in some people in dark conditions there is a decrease in alpha-wave activity of the brain.
The observed sensitivity to the polarity of the applied magnetic field suggests a mechanism based on magnetite. However, the existence of the human magnetic sense itself and any underlying mechanism is still far from clear.
To establish the existence and underlying mechanism of human magnetic sensing, we studied magnetic orientation in males, who showed remarkable magnetic sensitivity by combining the swivel chair method with the two alternative forced choice (2-AFC) paradigm, using oscillating magnetic fields as a diagnostic tool for a magnetic field resonance mechanism such as the radical pair mechanism.
Differential Sensitivity in Ambient Orientation Responding to GMF
Male subjects were starved or fed normal food, then tested using the swivel chair method in combination with the 2-AFC paradigm, which required subjects to choose one of two directions on the north-south magnetic axis.
During the association phase of the experiment, the subjects with their eyes closed and wearing headphones were aligned by the experimenters in such a way as to face the northern magnetic field, sitting on a swivel chair, and depending on the session, they were either conditioned to associate this direction with food or were not conditioned.
During the testing phase, during which “modulated” magnetic north was randomly set to true magnetic north or true magnetic south, subjects were asked to indicate the direction of the modulated magnetic north without reference to other information, including visual and auditory cues. The test was initially performed in full visible light (350-800 nm) (Table S1, #1 and Fig. S1A).
Subjects who were fasted to obtain a significant reduction in blood glucose (Table S2) were divided into two groups.
Group 1 (Fig. 1B, left, n = 20, about 60%) showed a significant increase in the ability to correctly orientate when associated with food compared to subjects who were not conditioned, while group 2 (Fig. 1B, right, n = 14, about 40%) showed a significantly lower level of food association (see Figures S2 and 1C for subject clustering).
In our previous study, under full wavelength conditions and light >400nm but not >500nm, most subjects showed significantly correct magnetic orientations with food association, while the rest did not.
In an attempt to objectify the clustering of subjects in the present study, principal component analysis of data recorded for fasted subjects with and without food association under full wavelength conditions and >400 nm light, as shown in Fig. 2A,C, made it possible to obtain two groups of subjects (Fig. 1C).
The results shown in fig. 1B are consistent with a reanalysis of relevant data from our previous study31 (Fig. S3) and show that fasting males with a food association were grouped into two groups; one group showed a significant GMF orientation to modulated magnetic north along the magnetic north-south axis, while the other did not.
In contrast, when subjects were fed normally (Table S2), group 1 but not group 2 showed a significant decrease in the rate of correct orientation with food association (Figure 1D).
The subjects were then tested to determine the modulated magnetic north, arbitrarily set on the true magnetic east-west axis. Like the results in Fig. 1B, the speed of orientation with association with food increased in group 1 and decreased in group 2, compared with no association with fasting (Figure S4, Table S2).
In our previous study, the ambient GMF was considered to be the unconditioned stimulus during the association phase. Therefore, we examined whether the perception of the surrounding GMF during association is necessary for the correct magnetic orientation along the magnetic north-south axis, as shown in Fig. 1b.
Under conditions of near-zero GMF during the association phase, none of the fasting groups showed a significant difference in the rate of correct orientation with and without association with food (Fig. 1E), indicating that perception of environmental GMF prior to the test was necessary for correct magnetic orientation in both groups.
These results indicate that there are two groups with different magnetic sensitivities when targeting the surrounding GMF depending on the nutritional context.
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