Abstract
Correlational evidence in non-human primates has reported increases of fronto-parietal high-beta (22–30 Hz) synchrony during the top-down allocation of visuo-spatial attention. But may inter-regional synchronization at this specific frequency band provide a causal mechanism by which top-down attentional processes facilitate conscious visual perception? To address this question, we analyzed electroencephalographic (EEG) signals from a group of healthy participants who performed a conscious visual detection task while we delivered brief (4 pulses) rhythmic (30 Hz) or random bursts of Transcranial Magnetic Stimulation (TMS) to the right Frontal Eye Field (FEF) prior to the onset of a lateralized target. We report increases of inter-regional synchronization in the high-beta band (25–35 Hz) between the electrode closest to the stimulated region (the right FEF) and right parietal EEG leads, and increases of local inter-trial coherence within the same frequency band over bilateral parietal EEG contacts, both driven by rhythmic but not random TMS patterns. Such increases were accompained by improvements of conscious visual sensitivity for left visual targets in the rhythmic but not the random TMS condition. These outcomes suggest that high-beta inter-regional synchrony can be modulated non-invasively and that high-beta oscillatory activity across the right dorsal fronto-parietal network may contribute to the facilitation of conscious visual perception. Our work supports future applications of non-invasive brain stimulation to restore impaired visually-guided behaviors by operating on top-down attentional modulatory mechanisms.
Highlights
High-level cognitive functions, such as spatial attention orienting or access to perceptual consciousness, cannot solely rely on the activity of single cortical regions but require the integration of processes occurring across widely distributed cortical nodes organized in complex brain networks[1,2]
Statistical analyses on topographic maps suggest that random Transcranial Magnetic Stimulation (TMS) patterns increased synchronization around 30 Hz between the right Frontal Eye Field (FEF) and fronto-parietal regions in the left hemisphere
Statistical analyses on time–frequency datasets (Fig. 3) confirmed that, compared to random TMS bursts, rhythmic TMS patterns increased right fronto-parietal synchrony only during the delivery of active stimulation and that such effects operated within a frequency band restricted to high-beta (24–45 Hz) oscillations (Fig. 3A)(cluster T-stat = 279.485, p-value = 0.001, Cohen’s d = 1.235)
Summary
High-level cognitive functions, such as spatial attention orienting or access to perceptual consciousness, cannot solely rely on the activity of single cortical regions but require the integration of processes occurring across widely distributed cortical nodes organized in complex brain networks[1,2]. Models have claimed that when two natural cortical oscillators synchronize in frequency and/or in phase, the spikes generated by a first group of neurons will reach well-synchronized neurons within a target population at their peak of excitability, ensuring a higher gain in information transfer and, more efficient communication This so called model of communication-through-coherence[7,8] has been hypothesized to be important in mediating top-down modulations (e.g. by attentional or perceptual processes) of inputs signals entering primary sensory a reas[10]. Experimental data in support of long-distance synchronization during visual perception and the orienting of attention have been collected both in animal models[11,12,13] and humans[14,15,16] The former evidence suggests that, in such processes, fronto-parietal regions synchronize at a beta or gamma frequency band (ranging from 15 to 60 Hz) during episodes of attentional orienting or perception. These reports associated synchronization with specific behaviors solely on the basis of their co-occurrence in time, an approach which has proven unable to distinguish causal contributions of oscillatory activity from potential epiphenomena
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
