[The EEG frequency spectra during the perception and mental rotation of 2- and 3-dimensional objects]

The EEG spectral power in 4 frequency ranges (8-13, 15-25, 25-35, and 35-45 Hz) was studied during mental rotation of two- and three-dimensional objects. Only those EEG segments were analyzed which corresponded to the tasks with similar time of solving. The EEG spectral power of the alpha range was higher under control conditions than during task solving. The spectral power in the range of 15-45 Hz was higher under the operation than under the control conditions. This finding confirms the assumption that EEG desynchronization in the alpha range is accompanied by the high-frequency synchronization. The EEG high-frequency power was higher during mental rotation of two-dimensional objects than three-dimensional ones. Since the angular difference between the two-dimensional objects was larger than between the three-dimensional ones, the rotation angle rather than the "depth" of space increased cortical activation. Under experimental conditions, EEG spectral power in the range of 15-45 Hz was always the highest in the occipital areas, which was associated with the visual modality of stimuli. The EEG spectral power in the gamma range (35-45 Hz) was substantially higher at the first second of operation as compared with the second one testifying that EEG changes in this range are more related with the processes of perception and recognition than with mental operations with images.