49

The History of Bioelectromagnetism

with commercial pulsed devices approved by the Food and Drug Administration (FDA). In 1979, FDA-

approved devices with pulsed magnetic felds were designed to stimulate bone growth.

2.4.2.2 Electromagnetic Stimulation

In the past, electricity could be easily generated and controlled, which led researchers to investigate

the efect of electricity on biological systems. Afer the demonstration of the existence of the electro­

magnetic waves (called Hertzian wave) made by Heinrich Rudolf Hertz, the researchers were engaged

in developing methods for the production of Hertzian waves, and they suggested various applications

of the newly developed method. Naturally, the researchers who had interest in the biological efects of

electricity soon shifed their interest to the biological efects of electromagnetic waves. So, the existence

of electromagnetic waves led to the development of the research of electromagnetic stimulation.

In 1902, Berthold Beer (1859–1922), Vienna, Austria, reported that phosphenes could be produced by

applying a magnetic feld to the head (Beer, 1902). He and Adrian Pollacsek (1850–1921), both psychia­

trists, got the frst patent application for use of magnetic coils to treat psychological disorders, depres­

sion, and neuroses, known as magnetic feld therapy.

Since the late nineteenth century, the inductive brain stimulation had been known. In 1896, d’Arsonval

attempted for the frst time to stimulate the retina with a non-invasive applied magnetic feld. When a

human head was placed within a strong time-varying magnetic feld generated by a large coil carrying

30 A at 42 Hz, 110 V, human perceived a fickering visual sensation. d’Arsonval called this phenomenon

“magnetophosphene.” Te retina is known to be very sensitive to stimulation by induced current. Tis

phenomenon is the visual sensation induced in the human brain. Tis was the frst magnetic inductive

stimulation efect to the retina of the nervous system.

Unaware of d’Arsonval’s experiments, Silvanus Phillips Tompson (1851–1916), professor of Physics

at the City and Guilds Technical College in England, induced magnetophosphenes (Tompson, 1910).

He constructed a coil consisting of 32 turns of stranded copper wire (cross-sectional area of 0.2 square

inch), which was wound on the cylinder with an internal diameter of 9 and 8 inches in length. He

applied up to 180 A with 50 Hz, which produced an rms feld strength of 1,000 Gauss at the center of

the coil. Te magnetic feld strength at the mouth of the coil was about two-thirds of this value. During

the experiments, the subjects closed their eyes in a darkened room, and inserting the head into the coil

produced “a faint fickering illumination, colorless or of a slightly bluish tint.” Even in daylight with the

eyes open, the visual sensation of fickering superposed the ordinary vision.

Carl Edward Magnusson (1872–1941), professor of Electrical Engineering, and H.C. Stevens, University

of Washington, carried out the phosphene studies with a large coil which was lowered over the subject’s

head (Magnusson and Stevens, 1911, 1914). When direct current fow in the coil was given, no phosphene

was perceived. However, when direct current fow was initiated, and interrupted, phosphene was seen.

Further, they carried out experiments to check the importance of frequency and feld strength in pro­

ducing phosphene. Te phosphene appeared when the magnetic feld frequency was below 25 Hz, and

appeared brighter with a 20–30 Hz current at a given feld strength.

More than 30 years afer, Horace Basil Barlow (1921–2020), a British visual neuroscientist, University

of Cambridge, and his co-workers described magnetophosphenes. Barlow was the great-grandson of

Charles Darwin. Using alternating magnetic felds of variable frequency, they compared the proper­

ties of the sensations thereby produced, with those produced by passing sinusoidal electric currents

through the head (Barlow et al., 1947). Te magnet had a coil of 397 turns of 16-gauge copper wire. Te

coil had 10.5 cm of inner diameter and 20.7 cm of outer diameter and was 7.3 cm long. A laminated core

of 5.3 × 2.9 cm in cross section and 37 cm long was placed inside the winding. Te subject was seated with

his temple close to the core of the magnet. In this situation, they could obtain up to 900 Gauss with 20

A (60 Hz). Phosphenes were perceived at 20 A of a 60 Hz sinusoidal current. To illustrate the phosphenes

with electric stimulation of the retina by passing electric current through the head, Barlow placed an

active electrode on the side of the forehead and a reference electrode on the back of the forearm. Tese

electrodes were copper discs 3 cm in diameter covered with cloth soaked in saturated NaCl solution.