Working-memory load and dimensional complexity of the EEG.

This investigation shows that a working-memory load induced by a memory scanning task has an effect on nonlinear descriptors of the EEG dynamics. The effect was locally specific above the fronto-temporal (right) cortex and it may be described as a reduction in the dimensional complexity of cortical brain activity. The meaning of the effects seems to differ from that of EEG spectral power, which varied with time during the experiment and not with changes in the working-memory load conditions. Behaviorally controlled over- and underload led to increased variance of the dimensional complexity, thus indicating that dimensional complexity correlates more closely with actual performance than with more general descriptions of brain states. Habitual response speed had an effect at the parietal lead, thus indicating that fast responders reduced their dimensional complexity as the task demand increased. In contrast, the slower responders showed no such definite trend.