Variation in length of alpha waves reveals how forebrain activity is organized

Background 

The cerebral cortex is composed of functional units known as columns. The "two levels" hypothesis states that the activity in a column is either at a high level or at a normal, relatively low level. Measurements indicate that the duration of the high activity in a column is around 450 ms. The number of highly active columns is often 4–5. These data are from previous studies on alpha waves in electroencephalograms. The idea is that alpha waves are created when a regulating system keeps the number of highly active columns within proper limits. If this is true, then regulating signals determines the length of the alpha waves, which opens up for a possibility to test the hypothesis.

Methods and results 

Wavelengths were measured in sequences of alpha waves, and distinctive patterns in the wavelength variation were found. The elements of these patterns were repeated at intervals that exactly matched the predicted duration of high activity in individual columns.

Conclusions 

The discovery of patterns in the wavelength variation confirms the central part of the two levels hypothesis. The patterns reveal the actual number of highly active columns. Moreover, the duration of high activity in a column can be measured. Number and duration outside the optimal ranges may lead to a variety of symptoms.