Human scalp-recorded EEG may be a result of activity of weakly-coupled subsystems.

The correlation dimension of monopolar electroencephalogram (EEG) recordings (reference Cz) and EEGs obtained by applying the Laplacian operator to monopolar recordings, were compared in 11 healthy subjects at P3 and P4 electrode positions of the international 10-20 system. Values of correlation dimension averaged over ten 16-s epochs (8192 samples, 512 Hz) were estimated for each subject. Laplacian derivations demonstrated lower values of correlation dimension in comparison with monopolar EEG. Tests for non-linearity with phase-randomized surrogate signals did not reveal differences between both types of derivations. These data suggest that human scalp-recorded EEG may be a result of activity of weakly-coupled subsystems and are consistent with the view that the correlation dimension can be related to the number of active neuron groups contributing to the scalp-recorded EEG.