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Summary: Oscillatory neuronal synchronization, within and between cortical areas, may mediate the selection of attended visual stimuli. However, it remains unclear at and between which processing stages visuospatial attention modulates oscillatory synchronization in the human brain. We thus combined magnetoencephalography (MEG) in a spatially cued motion discrimination task with source-reconstruction techniques and characterized attentional effects on neuronal synchronization across key stages of the human dorsal visual pathway. We found that visuospatial attention modulated oscillatory synchronization between visual, parietal, and prefrontal cortex in a spatially selective fashion. Furthermore, synchronized activity within these stages was selectively modulated by attention, but with markedly distinct spectral signatures and stimulus dependence between regions. Our data indicate that regionally specific oscillatory synchronization at most stages of the human dorsal visual pathway may enhance the processing of attended visual stimuli and suggest that attentional selection is mediated by frequency-specific synchronization between prefrontal, parietal, and early visual cortex. [Copyright &y& Elsevier]

Summary Visual cortical areas subserve cognitive functions by interacting in both feedforward and feedback directions. While feedforward influences convey sensory signals, feedback influences modulate feedforward signaling according to the current behavioral context. We investigated whether these interareal influences are subserved differentially by rhythmic synchronization. We correlated frequency-specific directed influences among 28 pairs of visual areas with anatomical metrics of the feedforward or feedback character of the respective interareal projections. This revealed that in the primate visual system, feedforward influences are carried by theta-band (∼4 Hz) and gamma-band (∼60–80 Hz) synchronization, and feedback influences by beta-band (∼14–18 Hz) synchronization. The functional directed influences constrain a functional hierarchy similar to the anatomical hierarchy, but exhibiting task-dependent dynamic changes in particular with regard to the hierarchical positions of frontal areas. Our results demonstrate that feedforward and feedback signaling use distinct frequency channels, suggesting that they subserve differential communication requirements. [ABSTRACT FROM AUTHOR]

Summary: A central motif in neuronal networks is convergence, linking several input neurons to one target neuron. In visual cortex, convergence renders target neurons responsive to complex stimuli. Yet, convergence typically sends multiple stimuli to a target, and the behaviorally relevant stimulus must be selected. We used two stimuli, activating separate electrocorticographic V1 sites, and both activating an electrocorticographic V4 site equally strongly. When one of those stimuli activated one V1 site, it gamma synchronized (60–80 Hz) to V4. When the two stimuli activated two V1 sites, primarily the relevant one gamma synchronized to V4. Frequency bands of gamma activities showed substantial overlap containing the band of interareal coherence. The relevant V1 site had its gamma peak frequency 2–3 Hz higher than the irrelevant V1 site and 4–6 Hz higher than V4. Gamma-mediated interareal influences were predominantly directed from V1 to V4. We propose that selective synchronization renders relevant input effective, thereby modulating effective connectivity. [ABSTRACT FROM AUTHOR]