112
The Body Electric
DC THROUGH THE HEAD PARTIALLY AWAKENS THE SALAMANDER
In the course of these observations, I found that when the head volt-
age was dropping as a chemical anesthetic took hold, specific slow waves
always appeared briefly in the recordings. They were at the low end of
the delta frequencies, 1 cycle per second or even less, and they also
showed up when the voltage came back as the drug wore off. To find out
if these waves always signaled a major change in the state of con-
sciousness, I decided to use a standard amount of direct current to pro-
duce anesthesia, measure the amplitude (size) of the delta waves in the
EEG, and then add some one-second waves of my own to the current I
was putting into the animal's head. In other words, I would introduce
some "change-of-state" waves from outside and see if they produced a
shift in the EEG. I couldn't record the EEG simultaneously, because the
waves I added would appear on the trace, so I rigged up a switch to cut
out the added waves after a minute and turn on the EEG recorder at the
same time, without stopping the direct current that would keep the
salamander unconscious.
It seemed to work. The added waves markedly increased the ampli-
tude of the salamander's own deep-sleep delta waves. Was this an ar-
tifact? Were the added waves just causing an oscillation in the brain
currents that persisted after the external rhythms were removed? It
didn't seem likely, because the waves I added were at the change-of-state
frequency of 1 cycle per second, while the measured deltas were at the
deep-sleep frequency of 3. However, an additional test was possible. I
could add waves of other frequencies and see if they worked as well as 1
cycle per second. They didn't; in fact, as the frequency of the added
waves increased over that rate, the deep-sleep delta waves got smaller.
The one-second waves were a marker of major shifts in consciousness.
This line of work corroborated one of the main points of my hypoth-
esis. Direct currents within the central nervous system regulated the
level of sensitivity of the neurons by several methods by (hanging the
amount
of current
in one direction,
by changing the direction of the
current (reversing the
polarity),
and by modulating the current with