Electroencephalographic cartography. II. By means of statistical group studies-activation by visual attention

10 male volunteers, right-handers, mean age 30.4 years, were recorded in four successive sequences: under 'eyes closed' conditions, right and then left hemisphere, followed by an 'eyes open' situation with visual attention fixed on a cartoon, right and then left hemisphere recordings. Each EEG recording was made simultaneously over 16 EEG channels for each hemisphere, according to a protocol previously described as well as Fourier analysis and EEG mapping on a minicomputer (HP 5451 C, HP 1000). Each EEG recording was stored on a cartography data base, and 90 maps could be drawn from 10 spectral parameters applied to the raw EEG and 5 frequency bands. Permutation paired Fisher tests were applied to three main EEG parameters: mean centroid frequencies, RMS amplitudes in microvolts and relative (%) amplitudes. Activation of EEG in the 'eyes open' situation during visual fixation was found compared to the 'eyes closed' situation: decreasing dominant EEG frequency and low delta and theta mean frequencies, no change in a mean alpha frequency; increasing fast mean beta frequencies, together with a major decrease in theta, alpha, beta 1 amplitudes, and a concomitant increase in raw EEG, delta and beta 2 amplitudes. Finally, the percent alpha amplitude was decreased when other percent amplitudes were increased in delta, theta, beta 1 and beta 2 frequency bands. A symmetry between hemispheres was observed in the 'eyes closed' situation. Averaged EEG maps between subjects illustrate these findings, especially relative (%) alpha amplitude maps and also maps of coefficients of resonance of the alpha rhythm.