The study from Siegel et al. (2008) provided one of the first evidence for a modulation of phase coherence induced by attention with different spectral signatures and stimulus dependence between cortical areas. Indeed, Siegel et al. recorded MEG data in eight subjects performing a motion discrimination task, in which they had to discriminate the motion direction of a cloud of dots in the cued hemifield ignoring the uncued hemifield. Coupling between five regions specifically implicated in the attention mechanisms and visual motion processing (see Figure 8 for details on the regions) was estimated through phase coherence, either in the stimulus or in the delay interval. A relative enhancement of phase coherence was found at high frequencies (35–100 Hz) and a relative decrease was found at low frequencies (5–35 Hz) in the hemisphere contralateral to the attended hemifield (Figure 8). Specifically, in the delay interval a reduction of gamma band connectivity was observed in the hemisphere ipsilateral to the cued hemifield between the posterior Intra Parietal Sulcus (pIPS) and middle Temporal (MT+), sustained also during the stimulus presentation, and between FEF
