BRAIN RHYTHMS—ADRIAN 459 
we 
must then decide which should have the main share of the attention, 
its function resembling that of a central university committee which 
has to decide which branch of learning should be supported by the 
next benefaction. 
The visual stimuli always get the lion’s share. If they are at all 
interesting, the central region will suppress the « rhythm over the 
occipital area, so that the visual pattern has a considerable part of the 
cortex set free for its analysis. When the visual pattern ceases to be 
interesting and the attention is directed to sounds or other sensory 
messages, the occipital lobe is not turned over to those but is filled 
again with the a rhythm. This is shown very clearly in records in 
which the visual waves are made recognizable by the use of a flicker- 
ing light, and if the flicker happens to be at twice the « rate a partial 
diversion of attention will be enough to give the large compound 
waves at the a frequency. 
Apparently the occipital part of the brain is used to analyze sights, 
and sights only. What parts deal with the patterns aroused by 
sound and touch we cannot yet say. The areas seem too small to be 
easily detected, and must certainly be much smaller than the areas 
which deal with vision. On the other hand, a concentrated mental 
effort may sometimes abolish the « rhythm although the eyes remain 
shut. Presumably in this case the whole of the « area may be turned 
over to nonvisual activities. 
There are still many gaps in the evidence, but there is much to 
support the view here put forward, namely, that there is a deep- 
seated part of the brain which contains the mechanism by which 
attention is directed one way or the other, and that the a rhythm is 
under the control of this region, if it is not directly produced by it. 
If this is so, it is not difficult to understand that abnormalities in the 
« rhythm are often associated with abnormal kinds of behavior. The 
most valuable application of the electroencephalogram in medicine 
is in the localizing of diseased regions and tumors of the brain by the 
change in the character of the waves. Another is its use in detect- 
ing the sudden explosive discharges of the nerve cells which occur in 
the brains of epileptics. But quite apart from such obvious disorder 
of the brain cells, the electroencephalogram may show an « rhythm 
which is definitely abnormal, irregular, faster or slower than usual 
or with odd-shaped waves, and in a significant proportion of the 
subjects who give such records there are abnormalities in the mental 
or emotional sphere which may be a serious handicap. There are, of 
course, many factors besides the constitution of the brain which de- 
termine whether we react like our fellows or not, but the brain is a 
not unimportant factor and the electroencephalogram seems to offer a 
means of assessing some of its deviations from the normal. It re- 
