Stimuli are selected through selective synchronization: An article in the journal NEURON demonstrates how selective synchronization between brain areas can modulate the effective connectivity between them.
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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.
Differences in synchronisation between areas in the visual system of a monkey, depending on attention (further explanation in research paper)
Conrado A. Bosman, Jan-Mathijs Schoffelen, Nicolas Brunet, Robert Oostenveld, Andre M. Bastos, Thilo Womelsdorf, Birthe Rubehn, Thomas Stieglitz, Peter De Weerd, Pascal Fries (2012) Attentional Stimulus Selection through Selective Synchronization between Monkey Visual Areas. Neuron 75 (5), pp. 875-888