Magnetic field effects on biomolecules, cells, and living organisms.

This article surveys three major areas of biomagnetic research: (a) the magneto-orientation effect; (b) the role of the geomagnetic field in bird orientation and navigation; and (c) the biological effects of extremely low-frequency magnetic fields. The magneto-orientation effect is caused by diamagnetic anisotropy of highly ordered biological structures, such as visual photoreceptor and chloroplast membranes, in a homogeneous magnetic field of about 10 kG. While it is not possible to orient the individual constituent molecules with such a field because of thermal fluctuation, these ordered structures can be oriented as a whole by virtue of summing the anisotropy over a large number of mutually oriented molecules. While the magneto-orientation effect seems to require the use of unphysiologically strong magnetic fields, certain birds apparently have highly sensitive sensors to detect the geomagnetic field for the purpose of orientation and navigation. However, the advances in this latter field were made mainly in the behavioral studies; the magneto-sensors the the neural mechanisms remain elusive. A number of candidates of the sensors are evaluated. We suggest that pecten oculi, which is unique to avian eyes, should not be overlooked for its possible role as a magneto-sensor based on the magneto-orientation effect. Birds primarily use a static (DC) magnetic field for orientation, but recent investigations indicate that weak alternating (AC) magnetic fields with extremely low frequency (ELF) may have hazardous health effects. Such reports are often received with skepticism, because the effects usually involve magnetic energies that are less than the kT energy. However, some of the in vitro studies yield experimental results that are too significant to be ignored. Here, we propose an argument to explain why low-level magnetic fields can be detected without being overshadowed by thermal noises. Relevance of biomagnetic research to the development of biosensors and novel computational paradigms is also discussed.