Traveling waves in attention networks inherit the rhythms of sensory systems

Abstract

Attention emerges from coordinated activity across distributed brain regions, each with their own intrinsic rhythm: alpha (7-12Hz) in visual cortex and theta (3-7Hz) in auditory cortex. When attention is sustained on a visual location, alpha power increases over the corresponding ipsilateral hemisphere, a robust neurophysiological marker of sustained visuospatial attention named alpha lateralization. Hemispheric asymmetry during sustained attention was recently also reported for anterior-to-posterior alpha traveling waves -smooth phase shifts across the cortex. This finding suggests that traveling waves support top-down inter-areal communication within the attention network. Here we asked whether traveling waves indeed reflect top-down attention signals or are merely a byproduct of sustained visuospatial attention. We manipulated attention through different sensory modalities (auditory cueing and visual stimulation), thus engaging different sensory cortices, while maintaining the task as visual discrimination. Using electroencephalography, we tested the hypothesis that if traveling waves reflect attention signals within the network, their frequency should follow the intrinsic rhythm of the engaged sensory system: theta for auditory cueing and alpha for visual stimulation. If instead they are a byproduct of attention allocated to visual information, their frequency should remain in alpha. Our results support the former: auditory cueing led to lateralized theta traveling waves, while visual stimulation produced lateralized alpha traveling waves. Crucially, traveling-wave lateralization in both frequencies correlated with trial-by-trial alpha power lateralization. Together, attention signals appear to propagate as waves at the intrinsic rhythm of the engaged sensory system and locally modulate alpha power lateralization in task-relevant visual regions.