67

The History of Bioelectromagnetism

 

by both groups was limited by the complexity of the gradient detection, imperfect coil cancellation, and

feld distortion due to ferrite which was necessary to raise the heart signal waveforms above the amplifer

input noise (Cohen, 1969). To overcome these limitations, a magnetically shielded chamber with a 2.23 m

inner size of the room was used. It consisted of two cubic shells of 1.5 mm thick ferromagnetic shield­

ing and one layer of aluminum. In this chamber, David Cohen recorded the MCG by a magnetometer

which is an air-core with a 200,000 turn coil of 5 cm in length and 8 cm in diameter (Cohen, 1967a, b).

Ten, Cohen described frst the magnetic feld of the brain’s spontaneous α-rhythm with an induction

coil magnetometer using this chamber (Cohen, 1968). Later, Cohen moved to MIT, and there he built a

more conventional fve-layer shielded room with a SQUID magnetometer. Te introduction of a SQUID

magnetometer gave the increase in sensitivity of biomagnetic measurements (Zimmermann et al., 1970).

SQUID device works at the liquid helium temperature, −270°C, and detects extremely low magnetic

felds ~10⁻⁹ T. Cohen and his co-workers recorded frst human MCG with SQUID in 1969 (Cohen et al.,

1970). Te introduction of SQUID and the work of Cohen and Zimmerman in MIT was a breakthrough

in biomagnetism. Cohen and James Edward Zimmerman (1923–1999) recorded MCG with a SQUID

magnetometer in this shielded room. Cohen is considered to be the pioneer in biomagnetism.

From these pioneering investigations with the newly developed SQUID in the 1970s, biomagnetism

became a more popular research feld. Many laboratories developed SQIUD-magnetometers for bio-

magnetic investigations. Te frst biomagnetic conference took place at MIT on August 8–11, 1976, as an

International Workshop (Cohen, 2004). Tere were only 23 attendees: from USA 15, Finland 3, Canada 2,

France 2, and Japan 1. Te attendee from Japan was Makoto Kotani, professor and later the President

of Tokyo Denki University, who is the pioneer in the research of biomagnetism in Japan (Kotani, 2011;

Uchikawa, 2020). Topics in this workshop were MCG, magnetoencephalography, and SQUID. Although

the frst Workshop was small, the Workshop became a regular Conference. Te International Conference

on Biomagnetism (BIOMAG 2022) will he held in Melbourne, Australia in 2022.

During the 1980s, research groups in biomagnetism grew steadily all over the world and published a

number of studies obtained with single-channel SQUID magnetometers. In this way, the frst measure­

ments were performed with a single-channel magnetometer. Afer that, the instrumentation gradually

improved from single-channel to multi-channel magnetometers. All commercially available multi­

channel systems are based on low-temperature SQUIDs. Now, 275-channel SQUID magnetometers are

available for medical uses.

2.5.2.4 Non-Invasive Electric and Magnetic Stimulations

Te early history of electromagnetic stimulation was reviewed in Section 2.4.2. Te use of the Transcranial

Electrical Stimulation for therapy goes back to the discovery of electrosensitive animals such as the tor­

pedo fsh. Tis electrotherapy continued until the end of the seventeenth century. More than 200 years

ago, Luigi Galvani and his nephew, Giovanni Aldini, used electrical stimulation to improve melan­

choly in patients with invasive electric stimulation. Transcranial Direct Current Stimulation (tDCS)

as the kind of transcranial electrical stimulation has been considered a neuro-modulatory interven­

tion. In 1938, the use of electrical stimulus treatment (ECT) in epilepsy and in mental illnesses was

introduced by two Italian physicians, Ugo Cerlett (1877–1963), neurologist, professor at University of

Rome La Sapienza, Rome, and his student Lucio Bini (1908–1964) (Rowbottom and Susskind, 1984).

ECT is a therapy in which electric current is used to provoke a seizure for a short duration. Tis newly

developed ECT spread rapidly through Europe and North America in the 1950s and 1960s. ECT was

cleared by the FDA for the treatment of depression as a preamendment device. ECT has been used to

treat a variety of psychiatric disorders: depression (unipolar and bipolar), schizophrenia, bipolar manic

(and mixed) states, catatonia, and schizoafective disorder. Te wave-forms for ECT are of high current,

approximately 800 mA with trains (AC or pulsed bursts) lasting 1–6 Hz. Te electrodes are placed either

unilaterally or bilaterally on the cranium. Te non-invasive techniques had been investigated only in

a small number of studies. During the operation of tDCS, a weak-amplitude direct electric current is

passed over the brain through two surface electrodes placed on the scalp. Now, non-invasive methods