Dissociated alpha-band modulations in the dorsal and ventral visual pathways in visuospatial attention and perception

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Modulations of occipito-parietal alpha-band (8-14 Hz) power that are opposite in direction (alpha-enhancement vs. alpha-suppression) and origin of generation (ipsilateral vs. contralateral to the locus of attention) are a robust correlate of anticipatory visuospatial attention. Yet, the neural generators of these alpha-band modulations, their interdependence across homotopic areas, and their respective contribution to subsequent perception remain unclear. To shed light on these questions, we employed magnetoencephalography, while human volunteers performed a spatially cued detection task. Replicating previous findings, we found alpha-power enhancement ipsilateral to the attended hemifield and contralateral alpha-suppression over occipito-parietal sensors. Source localization (beamforming) analysis showed that alpha-enhancement and suppression were generated in 2 distinct brain regions, located in the dorsal and ventral visual streams, respectively. Moreover, alpha-enhancement and suppression showed different dynamics and contribution to perception. In contrast to the initial and transient dorsal alpha-enhancement, alpha-suppression in ventro-lateral occipital cortex was sustained and influenced subsequent target detection. This anticipatory biasing of ventro-lateral extrastriate alpha-activity probably reflects increased receptivity in the brain region specialized in processing upcoming target features. Our results add to current models on the role of alpha-oscillations in attention orienting by showing that alpha-enhancement and suppression can be dissociated in time, space, and perceptual relevance.