The Circuit of Awareness 111
Certainly the falling voltages in anesthetized salamanders supported this
idea. The question was: Did the change in the current produce anesthesia?
Apparently it did, for when I passed a minute current front to back
through a salamander's head so as to cancel out its internal current, it
fell unconscious. How this state compared with normal sleep was impos-
sible to tell, but at least the animal was clinically anesthetized. As long
as the current was on, the salamander was motionless and unresponsive
to painful stimuli.
Was this real anesthesia, or was the animal just being continuously
shocked? This certainly didn't seem to be the case, but the observation
was so important and so basic to neurophysiology that I had to be sure.
It was no easy task, however, for there were, and still are, few objective
tests known for anesthesia, especially in salamanders. Brain waves had
turned out to be useless in gauging depth of anesthesia in humans, be-
cause the one good marker—very slow delta waves—only showed up
when the patient was dangerously close to death. Lacking any better
idea, however, I used my new multi-electrode monitor to make EEG
recordings of chemically anesthetized salamanders and found that they
showed prominent delta waves even though they all recovered nicely.
Delta waves would be my marker. The idea worked beautifully. Very
small currents gave me delta waves on the EEG, the waves got bigger as
I increased the current, and they all correlated with the animal's periods
of unresponsiveness.
,
.
DC THROUGH THE HEAD ANESTHETIZES THE SALAMANDER
This result naturally led to the question: Did chemical anesthetics
work by stopping the brain's electrical current? I couldn't see any way to
get direct evidence one way or the other, but I thought maybe chemical
anesthesia could be reversed by putting current into the brain in the
normal direction. I found this could be done only to a certain extent. I
could get a partial return of the higher frequency waves in the EEG, and
the anesthesia seemed to become shallower, but I couldn't get a drugged
salamander to wake up and walk away.