The spatial and temporal variability of the magnetoencephalogram alpha rhythm in the normal human subject

Using one-channel SQUID biomagnetometer alpha rhythm was recorded in five healthy men and eight healthy women. Maps of distribution of maximum values of mean MEG amplitudes were analyzed. Most frequently MEG maxima predominated in the parietal parts of the head. Less frequently they were found in the occipital parts. In single instances they could be found in the posterocentral sections and on the midline. In most cases an amplitude interhemispheric asymmetry of extrema was revealed. In men the mean amplitude of the alpha-rhythm predominated more frequently on the left side and in women--on the right one. The map of distribution of mean amplitudes was stable at least during two weeks. Narrow-band filtration allowed to reveal up to three discrete amplitude modes. At definite frequencies the MEG amplitude was continuously stable during several seconds.