Recently technological advances allow monitoring different physiological variables non-invasively and continuously over time. Temporary fluctuations in variables whose statistical study can be approached as time series, allow understanding the underlying dynamics of the organ generating such fluctuations. Here we study the variability of brain networks based on using electroencephalographic (EEG) records from in two groups of people whose extreme ages were 10 (four children) or 70 year old persons under good physical and mental health, according to a set of tests previous to the recordings. The EEG recording protocol used was the international 10-20 configuration for nineteen electrodes. The time series were filtered to obtain the alpha range (8-13 Hz) from non-overlapping time intervals Δ t, each consisting of N data points. The spatial correlation matrix C was calculated for each interval. Our results show the loss of variability of the functional brain network in the 70 year old population when compared with the children population. This method may now be extended to analyse responses of people of a wider range of ages and under different cognitive situations. [ABSTRACT FROM AUTHOR]