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Bioelectromagnetism

for measurement of brain activity through tDCS and TMS are efective methods. Both tDCS and TMS

are now widely used for rehabilitation treatments in clinic. Furthermore, they can be used to evaluate

neuronal activity in the brain, brain connectivity for diagnostic purpose.

Now, we introduce the earliest demonstrations of magnetic stimulations in animals. It has passed

over half a century from D’Arsonval’s demonstration of magnetic stimulation in human retina. In

1959, Alexander Kolin (1910–1997), a Russian-born Germany-US biophysicist, from the University of

California, accomplished the frst magnetic stimulation of a frog’s sciatic nerve and muscles submerged

in Ringer’s solution by means of time-varying magnetic felds (Kolin et al., 1959). He presented that

this efect is due to eddy current induced in conductive tissue and their surroundings. In the past, he

invented in 1936, the electromagnetic blood fow meter and isoelectric focusing. For this invention, he

was the candidate for the Nobel Prize.

In 1965, Reginald G. Bickford, electroencephalographer, and B. D. Fremming stimulated the periph­

eral nerves in animals and humans using a pulsed magnetic feld lasting 40 ms (Bickford and Freming,

1965). Te resulting long-lasting activation interval made it impossible to record nerve or muscle action

potentials, and the work was not pursued further. In 1973, Per Åke Öberg of Linköping University inves­

tigated the magnetic stimulation on excitable tissues in frog nerve muscles which were placed in high-

frequency magnetic felds of 1 kHz–1 MHz (Öberg, 1973). Shoogo Ueno, professor at Kyusyu University

and later at the University of Tokyo, and his co-workers carried out experiments to measure action

potentials of lobster giant axons placed on magnets with time-varying magnetic felds (Ueno et al.,

1981, 1984, 1986). Afer the study of this single nerve axon, Ueno proposed a new type of magnetic nerve

stimulation (Ueno et al., 1988). In 1988, in order to more precisely localize the stimulating region over

the head, Ueno introduced the magnetic stimulation with a fgure-of-eight coil as the stimulating coils

(Ueno et al., 1988). Figure 2.15 shows a TMS of the primary motor cortex with the fgure-of-eight coil.

Ten, they succeeded in stimulating the human cortex with a 5 mm resolution (Ueno et al., 1990). Ueno

soon improved it by changing the coil arrangements. Te fgure-of-eight shaped coil has the merit to

induce more concentric electric feld (~mm in size) than that of a circular single coil, which results in

better focusing and control of the spatial extent of the excitation.

FIGURE 2.15 TMS of the primary motor cortex (From Ueno)