Temporal evolution of alpha and beta bands during visual spatial attention.

Event-related potentials (ERPs) are an electrophysiological index of various cognitive processes such as attention. However, this kind of analysis does not allow observation of differences in the spectral content taking place during a sensory, cognitive or motor task. The goal of the present work was to compute the temporal dynamics of EEG oscillations using a technique called temporal spectral evolution (TSE). The electroencephalogram (EEG) was recorded during the presentation of flashed stimuli that were randomly presented to the left or right visual field. Subjects were asked to pay attention, alternately in different blocks of trials, to the left or to the right to detect an infrequent target. The results showed a decrease in the alpha band in a time window of 375-500 ms and an increase in the beta band at 500-875 ms after stimulus onset, for both attended and unattended stimuli. Statistical analysis showed that the decrease in alpha and the increase in beta were more marked during the attentional condition. In conclusion, these results demonstrate that the decrease in alpha band and the increase in beta band are electrophysiological markers of visual spatial attention.