Alpha-rhythm signs of time-related inhibition of visual attention orienting during cue-target spatial processing as indexed by EEG Wavelet analysis.

Previous research has indicated that visuospatial orienting of attention is related to brain EEG -frequency band. The most recent evidence points to a determining role of occipito-parietal α-band activity (8–14 Hz) in anticipatory orienting facilitation (α-power decreases) vs. inhibition (α-power increases). Yet, while such α-modulations are a common finding, the direction of modulation and its timing varies to a great extent across studies implying dependence on task demands. Furthermore, scarce knowledge is available about the power of this EEG oscillatory band in the diverse endogenous and exogenous orienting modalities and about its trend in time. In this study, nineteen students were recruited to investigate these matters. They were administered a modified version of Posner’s ANT (Attention Network Test) made up of diverse spatial cueing tasks priming the presentation of a target. The cue provides diverse spatial information as a function of task: namely, a CC (Central Cue) task, a NC (No Cue) task, and a LC (Local Cue) task. On each trial, the EEG was recorded from 128 scalp sites going from 100 ms before the cue to 1300 ms after it, a target being presented 500 ms after the cue, to which the participants had to respond motorically. We computed LC-CC and CC-NC difference waves to get access to the orienting system and the alerting system functionality, respectively. Wavelet Analysis was used to measure event-related -band oscillations power (in uV2/Hz) between 8 - 12 Hz, so to investigate its functional role and its effects on the Attention Networks, at 20 parietal-occipital (PO5h / PPO6h; POO9h / POO10h, PPO9h / PPO10h, PO9 / PO10, PO7 / PO8) and frontal (F5 / F6, FCC5h /FCC6h, AFF5h / AFF6h, FC5 / FC6 and FFC5h / FFC6h) sites. EEG time span was divided into four ranges: 0 - 240 ms, 240 - 500 ms, 500 - 800 ms, and 800 - 1300 ms. Interestingly, CC-NC condition showed the alerting system efficiency and, once the target was delivered, also the orienting system functions. This also provided us information on differences on target processing modes in time. The results pointed out that -band gradually decreased, reaching the lowest peak power in the 800 - 1300 ms latency range. A greater -band power was measured at parietal-occipital electrodes and for the CC-NC condition, in the left hemisphere both before and after the target (0 - 240 ms, 240 - 500 ms, 500 - 800 ms) delivery, and in the right hemisphere after the target appearance only (800 ms to 1300 ms). In conclusion,our findings provide support to an active facilitative versus inhibitory role of α-power decreases and increases and suggests that these attention-related changes are differentially deployed during anticipatory attention orienting to prepare versus maintain the cortex for optimal target processing.