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Electromagnetic Fields in Biological Systems
be realized that the actions of SMFs and time-varying magnetic fields differ from each
other in terms of the mechanisms fundamental to each.
Studies on the biological effects of magnetic fields have resulted in significant developments in the medical applications of SMF as well as EMF, after the development of
high-strength superconducting magnets. The three mainstays of such medical applications are TMS, MRI, and the measurement of biomagnetic fields with a superconducting quantum interference device (SQUID). These techniques have also contributed
much to the amazing progress made in understanding brain functions. The TMS locally
stimulates the human cerebral cortex with millimeter-order spatial resolution from a
figure-eight coil placed on the skull. A three-dimensional (3D) imaging of the brain
neuron function has been enabled by the utilization of SQUID in magnetoencephalography (MEG), functional MRI (fMRI), and current-distribution MRI. Results from TMS
and imaging studies indicate potential applications of biomagnetics in brain science and
clinical neuropsychiatry.
The technique of locally applying magnetic stimulation by a strong pulsed magnetic
field on the order of 1 T transcranially to the brain is called TMS. When a strong
electric current is applied to a figure-eight coil placed over the head for 150 milliseconds a pulsed magnetic field on the order of 1 T is produced; this field generates eddy
currents in the brain, which excite the nervous system or stimulate excitable tissues.
The first study of magnetic stimulation of the human brain was conducted by Barker,
Jalionus, and Freeston (1985) who utilized single coils for the purpose; hence, localized magnetic stimulation of a targeted portion of the human brain was impossible
in this study. The focal and vectorial magnetic stimulation of a human cortex using
a figure-eight coil was developed by the following groups of researchers: Ueno et al.
(1978); Ueno, Lovsund, and Oberg (1986); Ueno, Matsuda, and Fujiki (1989, 1990);
Ueno, Matsuda, and Hiwaki (1990, 1991); and Ueno, Tashiro, and Harada (1988); this
enabled the stimulation of the motor cortex of a human brain at 5-mm resolution.
Localized magnetic stimulation contributed to the creation of functional maps of the
motor cortex related to hand and foot areas. An optimal direction of probe placement for the targeting of stimulating currents, which induce neural excitation in each
functional area of the cortex, based on functional maps was observed, which is the socalled vectorial feature. Variations in the functional maps of the cortex with changes
in orientation of the stimulating current were observed as well. It is a proven fact that
the vectorial feature allows studies that reflect both functional and anatomical organizations of neural fibers in the brain. Localized magnetic nerve stimulation of the
brain is suitable for investigations of brain function and construction without causing
damage to any tissues.
3.3 Experimental Studies on Magnetic Field Effects
Recent advance of biological science and technology can help us understand magnetic
field effects more clearly. In this major section consisting of In Vivo Studies (3.3.1), and
Tissue, Molecular, and Cellular Studies (3.3.2), we provide an overview of a variety of
studies on magnetic field effects to explore the uderlying mechanisms and the recent
preclinical applications.
Electromagnetic Fields in Biological Systems
be realized that the actions of SMFs and time-varying magnetic fields differ from each
other in terms of the mechanisms fundamental to each.
Studies on the biological effects of magnetic fields have resulted in significant developments in the medical applications of SMF as well as EMF, after the development of
high-strength superconducting magnets. The three mainstays of such medical applications are TMS, MRI, and the measurement of biomagnetic fields with a superconducting quantum interference device (SQUID). These techniques have also contributed
much to the amazing progress made in understanding brain functions. The TMS locally
stimulates the human cerebral cortex with millimeter-order spatial resolution from a
figure-eight coil placed on the skull. A three-dimensional (3D) imaging of the brain
neuron function has been enabled by the utilization of SQUID in magnetoencephalography (MEG), functional MRI (fMRI), and current-distribution MRI. Results from TMS
and imaging studies indicate potential applications of biomagnetics in brain science and
clinical neuropsychiatry.
The technique of locally applying magnetic stimulation by a strong pulsed magnetic
field on the order of 1 T transcranially to the brain is called TMS. When a strong
electric current is applied to a figure-eight coil placed over the head for 150 milliseconds a pulsed magnetic field on the order of 1 T is produced; this field generates eddy
currents in the brain, which excite the nervous system or stimulate excitable tissues.
The first study of magnetic stimulation of the human brain was conducted by Barker,
Jalionus, and Freeston (1985) who utilized single coils for the purpose; hence, localized magnetic stimulation of a targeted portion of the human brain was impossible
in this study. The focal and vectorial magnetic stimulation of a human cortex using
a figure-eight coil was developed by the following groups of researchers: Ueno et al.
(1978); Ueno, Lovsund, and Oberg (1986); Ueno, Matsuda, and Fujiki (1989, 1990);
Ueno, Matsuda, and Hiwaki (1990, 1991); and Ueno, Tashiro, and Harada (1988); this
enabled the stimulation of the motor cortex of a human brain at 5-mm resolution.
Localized magnetic stimulation contributed to the creation of functional maps of the
motor cortex related to hand and foot areas. An optimal direction of probe placement for the targeting of stimulating currents, which induce neural excitation in each
functional area of the cortex, based on functional maps was observed, which is the socalled vectorial feature. Variations in the functional maps of the cortex with changes
in orientation of the stimulating current were observed as well. It is a proven fact that
the vectorial feature allows studies that reflect both functional and anatomical organizations of neural fibers in the brain. Localized magnetic nerve stimulation of the
brain is suitable for investigations of brain function and construction without causing
damage to any tissues.
3.3 Experimental Studies on Magnetic Field Effects
Recent advance of biological science and technology can help us understand magnetic
field effects more clearly. In this major section consisting of In Vivo Studies (3.3.1), and
Tissue, Molecular, and Cellular Studies (3.3.2), we provide an overview of a variety of
studies on magnetic field effects to explore the uderlying mechanisms and the recent
preclinical applications.