The Circuit of Awareness 113
slow waves. Moreover, we could exert the same control from outside by
putting current of each type into the head. This was exciting. It opened
up vast new possibilities for a better understanding of the brain. It was
still on the edge of respectability, too, since it was a logical consequence
of the work done by Gerard and his co-workers. The next experiment
was harder to believe, however.
I figured the brain currents must be semiconducting, like those in the
peripheral nerves. I thought of looking for a Hall voltage from the head
but reasoned the brain's complexity would make any results question-
able. Then I thought of using the effect backward, so to speak, measur-
ing a magnetic field's action on the brain rather than on the production
of the Hall voltage. Since the Hall voltage was produced by diverting
some of the charge carriers from the original current direction, a strong
enough magnetic field should divert all of them. If so, such a field per-
pendicular to the brain's midline current should have the same effect as
canceling out that normal current with one applied from the outside.
The animal should fall asleep.
THE HALL EFFECT—A TEST FOR SEMICONDUCTING CURRENTS
We tranquilized a salamander lightly, placed it on a plastic shelf be-
tween the poles of a strong electromagnet, and attached electrodes
to measure the EEC As we gradually increased the magnetic field
strength, we saw no change—until delta waves appeared at 2,000 gauss.
At 3,000 gauss, the entire BEG was composed of simple delta waves,
and the animal was motionless and unresponsive to all stimuli. More-
over, as we decreased the strength of the magnetic field, normal EEG
patterns returned suddenly, and the salamander regained consciousness
within seconds, This was in sharp contrast to other forms of anesthesia.