BRAIN RHYTHMS? 
By E. D. Aprian, O. M., F. R. S. 
University of Cambridge 
In 1929 Prof. Hans Berger, of the Psychiatric Institute at Jena, 
published the results of some work on which he had been engaged for 
many years. He had set out to record the electric currents devel- 
oped in the human brain, and had shown that if metal electrodes were 
fixed to the scalp, it was possible to detect a regular oscillation of elec- 
trical ‘potential which was not due to muscles or skin glands or any 
other source outside the skull, and could only have come from the 
nerve cells of the cerebral cortex. The oscillation had a frequency 
of 9-10 a second. It only appeared when the subject was at rest with 
attention relaxed and eyes closed; but it obviously represented some 
kind of continuous activity in the brain covering a fairly large area. 
What he discovered was then quite unexpected. It has made us revise 
many of our ideas about the brain and has brought us a little nearer 
to understanding what goes on in it. 
The oscillation, Berger’s a rhythm, represents a very small change 
of potential, about 50 microvolts, and a very small ebb and flow of 
current in the cerebral cortex. There is nothing unexpected in the 
fact that brain cells develop small currents when they are active, for 
all active cells do so. The unexpected thing is the regularity of the 
rhythm.. It is true that if it were not so regular it might never have 
been detected, but the regularity means that large numbers of brain 
cells must be working in unison at the same rate. We should have 
expected something much more complex and variable—activity vary- 
ing from moment to moment and from place to place—and not the uni- 
form pulsation shown in a typical record of the electroencephalogram. 
We should have expected this because the brain is a great sheet of 
nerve cells and interlacing nerve fibers, and its working must depend 
on the spatial distribution of activity in it. This is determined by 
the particular pathways which must be taken by the incoming and out- 
going messages, for the messages are all in the same form wherever 
they come from and it is because they arrive in different regions that 
1Friday Evening Discourse at the Royal Institution delivered on February 4, 1944. 
Reprinted by permission from Nature, vol. 153, March 25, 1944. 
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