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Geomagnetic Field Effects on Living Systems

at 1/r⁴ and “octuple” whose strength becomes weaker at 1/r⁵. In the gravitational feld, there is a single

“monopole” feld whose strength becomes weaker at 1/r², but in the GMF, such a monopole has not yet

been discovered and at least two poles always appear in pairs. He used this method to analyze the GMF

data measured around the world and proved that the main components of the GMF originated inside

the Earth, not from space. Furthermore, it was clarifed that about 80% of the components of the GMF

can be explained by the dipole MF originating from the inside of the Earth. Generally speaking, he is

considered to be one of the discoverers of the GMF.

Gauss has also developed a device that accurately measures the GMF. Tis device quickly spread

all over the world, and continuous measurements were made all over the world in the 1840s. In Japan,

measurements of the GMF began in Tokyo in 1883, but it became difcult to measure the GMF because

the noise of the EMFs became too strong due to the expansion of electric transmission lines and trams.

Terefore, since 1913, the Geomagnetic Observatory, which was relocated to Kakioka, Ishioka City,

Ibaraki Prefecture, has been measuring the GMF for more than 100 years (Suganuma, 2020).

It has been confrmed that various animals possess magnetoreception that perceives the direction,

strength, and location of the GMF. In many migratory birds, photosensitive chemical reactions involv­

ing the cryptochrome (CRY) favoprotein were thought to play an important role in the ability to sense

the GMF. In the case of Drosophila, CRY1 found in these fies mediates light-dependent magnetorecep­

tion in a wavelength-dependent manner (Gegear et al., 2008, 2010; Fedele et al., 2014a,b). Surprisingly,

this fnding was later extended to CRY2 by showing that monarch butterfy and human CRY2 overex­

pressed in CRY-defcient fies could restore magnetosensitivity and its light-dependency (Gegear et al.,

2010; Foley et al., 2011). In the case of monarch butterfies, although monarch butterfy CRY2 has been

shown to mediate light-dependent magnetosensitivity in the Drosophila cellular environment, similar

to human CRY2 (Gegear et al., 2010; Foley et al., 2011,2014a), monarch butterfies respond to a reversal of

the inclination of the GMF in a UV-A/blue light and CRY1, but not CRY2, dependent manner, and both

antennae and eyes, which express CRY1, are magnetosensory organs (Wan et al., 2021).

Humans are widely assumed not to have a magnetic sense for the GMF and also higher intensity

SMFs (Phillips et al., 2010). A research team of the University of Massachusetts Medical School exam­

ined the light-dependent magnetosensing potential of human CRY2 (hCRY2) (Foley et al., 2011). To

test whether the hCRY2 protein has similar magnetic sensory abilities, researchers have developed a

transgenic Drosophila model that lacks the native CRY but instead expresses hCRY2 (Foley et al., 2011).

Tus, they used hCRY2, which is abundantly expressed in the human retina, as a transgenic approach

(Foley et al., 2011). Using a previously developed behavioral system (Gegear et al., 2008, 2010), when the

CRY2 protein expressed in the human retina is transplanted into Drosophila, they examined whether

these transgenic fies could sense and respond to the MF generated by the electric coil (Foley et al., 2011).

Te results showed that the hCRY-rescued transgenic fies can sense the MF (Foley et al., 2011).

However, it remains unclear whether this function is translated into a biological response downstream of

the human retina (Foley et al., 2011). Tese fndings demonstrated that hCRY2 has the molecular capabil­

ity to function in a magnetic sensing system and may pave the way for further investigation into human

magnetoreception (Foley et al., 2011). Te light sensitivity of the human visual system has been shown

to be remarkably sensitive to the modulated direction of the GMF (Toss et al., 2000, 2002). Alternating

MFs signifcantly altered electroencephalogram (EEG) signals in several brain regions, indicating the

presence of “magnetosensory evoked potentials” (Carrubba et al., 2007; Mulligan and Persinger, 2012).

Do we humans really have the ability to sense the GMF? However, it has been estimated that humans

lack at the very least an active perception of the GMF (Nordmann et al., 2017). Nordmann et al. (2017)

emphasized that this complicates the design of experiments that aim to unravel specifc aspects of the

sensory modality, and compromises an experimenter’s ability to detect obvious artifacts. Te applica­

tion of magnetic stimuli risks EM induction in a recording electrode, which makes the interpretation of

electrophysiological data challenging (Nordmann et al., 2017). Anything from nT strength RF interfer­

ence to the chosen perfume of experimenters can render an assay useless (Engels et al., 2014; Pinzon-

Rodriguez and Muheim, 2017).