Experimental evidence for a power law in electroencephalographic $\alpha$-wave dynamics

We perform an experimental study of the time behavior of the $\alpha$-wave events occuring in human electroencephalographic signals. We find that the fraction of the time spent in an $\alpha$-burst of time size $\tau$ exhibits a scaling behavior as a function of $\tau$. The corresponding exponent is equal to 1.75$\pm$0.13. We therefore point out the existence of a new power law appearing in physiology. Furhtermore, we show that our experimental result may have a possible explanation within a class of Self-Organized Critical (SOC) models recently proposed by Boettcher and Paczuski. In particular, one of these models, when properly re-interpreted, seems to be consistent both with our result and a commonly accepted physiological description of the possible origin of $\alpha$-wave events.