Figure 5.

MEG directed connectivity confirms the reversal of DLPFC and aPFC information flow. GC and PSI were used to estimate the directed influences between the DLPFC and aPFC regions (as defined by the fMRI experiment) during task encoding. Note that these directed connectivity methods are correlational in nature and are not able to assess true causality (though modulation of these measures by experimental manipulation can strengthen that inference). A, GC of gamma power indicated that aPFC and DLPFC influence each other bidirectionally during encoding (largest p = 6e-37). There was a significant dominant influence from DLPFC to aPFC during the first novel task encoding screen and a significant dominant influence from aPFC to DLPFC during the second practiced task encoding screen. This supports the prediction of bottom-up information flow during novel task preparation and top-down information flow during practiced task preparation. See Tables 3 and 4 for details. Practiced task interactions may be delayed relative to novel task interactions because of the additional time necessary for retrieval of higher-level task information from LTM. B, The PSI statistic, an alternative to GC with fewer false positives for noisy data (Nolte et al., 2008), supports the GC finding. C, This reversal of information flow was also present during first trials and was significantly different between novel and practiced task preparation (p = 0.001). D, E, The gamma power estimates used for GC analysis (averaged by block) were significantly correlated between aPFC and DLPFC, indicating strong functional connectivity and supporting the conclusions based on GC and PSI.