This standard measure of functional connectivity, however, may be difficult to link to precise cognitive dynamics, because the connectivity may reflect a combination of several processes including response preparation, stimulus evaluation, attention, orientation, etc. Thus, we extend this connectivity measure to examine whether synchronization is modulated by an experimental variable (e.g., reaction time). The idea is that process-specific connectivity should be modulated by reaction time, whereas more general inducers of connectivity (e.g., orienting attention, general response preparation) should not be. Similar to the phase analysis above, this method tests the relationship between relative phase angles between seed (FCz) and target (F6 or other) electrode pairs and reaction time. The right three columns in Figure 6A show time–frequency plots of modulated phase synchronization between FCz (MFC) and F6 (lateral prefrontal cortex). This “response-modulated” functional connectivity increased prior to the response, and was strongest during cI trials (interaction term: F1,14 = 5.48, p = 0.035). This indicates that on a trial-by-trial basis, longer reaction times during high conflict situations were preceded by enhanced electrophysiological connectivity between medial frontal and lateral prefrontal regions. Topographical maps in Figure 6B show that this effect was localized primarily to anterior and lateral prefrontal sites.
