240
The Body Electric
conveys information in its fluctuations, it must be reflected by a mag-
netic field around the body, whose pulsing would reveal the same infor-
mation. When I first proposed this idea, many of my colleagues
dismissed it as rank nonsense. I couldn't prove them wrong, because
there were no instruments to measure a field as weak as that generated
by such small currents. Everyone knew the human body had no effect on
a compass needle or any other magnetic-field detector available at the
time.
Then, in 1964, a solid-state physicist named Brian D. Josephson in-
vented the electronic device now called a Josephson junction, a simple
item that won him a Nobel Prize. Basically it consists of two semicon-
ductors connected so that current can oscillate in a controlled fashion
between them. Today it has many applications, especially in computers.
When cooled near absolute zero in a bath of liquid helium, it becomes a
superconductor in which the current plays back and forth endlessly. Su-
perconduction is the passage of electrons through a substance without
the resistance normally found in any conductor. This apparatus, called a
superconducting quantum interferometric device, or SQUID for short, is
a magnetic field detector thousands of times more sensitive than any
previously known.
In 1963, G. M. Boule and R. McFee just barely managed to measure
the relatively large magnetic field produced by the human heart—using
the best old-fashioned instrument, a coil with 2 million turns of wire.
Then, in 1971, working in a null-field chamber, from which the earth's
magnetism and all artificial fields were screened out, Dr. David Cohen of
MIT's Francis Bitter National Magnet Laboratory, who'd been corre-
sponding with our lab since the early years, first used the SQUID to
measure the human head's magnetic field. Two kinds of magnetic fields
have been found. Quickly reversing AC fields are produced by the back-
and-forth ion currents in nerve and muscle. They're strongest in the
heart, since its cells contract in synchrony. The SQUID has also con-
firmed the existence of the direct-current perineural system, which, es-
pecially in the brain, produces steady DC magnetic fields one billionth
the strength of earth's field of about one-half gauss.
By 1975, Drs. Samuel Williamson, Lloyd Kaufman, and Douglas
Brenner of NYU had succeeded in measuring the head's field without a
shielded enclosure, even amid the electromagnetic noise of downtown
Manhattan. More important, they've found that the magnetoencepha-
logram (MHG)—a recording of changes in the brain's field analogous to
the EEG - is often a more accurate reflection of mental activity than the
EEG. Because the magnetic field passes right through the dura, skull