It is known that the default mode network (DMN) may be modulated by a cognitive task and by performance level. Changes in the DMN have been examined by investigating resting state activation levels, but there have been very few studies examining the modulation of effective connectivity of the DMN during a task in healthy older subjects. In this study we examined how effective connectivity changed in the DMN between rest and during a memory task. We also investigated whether there was any relationship between effective connectivity modulation in the DMN and memory performance, in order to establish whether variations in cognitive performance are related to neural network effective connectivity, either at rest or during task performance. Twenty-eight healthy older participants underwent a resting-state functional MRI (rfMRI) scan and an emotional face-name encoding task. Effective connectivity analyses were performed on the DMN in order to examine the effective connectivity modulation in these two different conditions. During the resting state there was strong self-influence in the regions of the DMN, whille the main regions with statistically significant cross-regional effective connectivity were the posterior cingulate cortex (PCC) and the hippocampus (HP). During the memory task the self-influence effective connectivites remained statistically significant across the DMN and there were statistically significant effective connectivites from the PCC, HP, amygdala (AM) and parahippocampal region to other DMN regions. We found that effective connectivities from PCC, HP and AM (in both resting state and during task) were linearly correlated to memory performance. The results suggest that superior memory ability in this older cohort was associated with effective connectity both at rest and during the memory task of three DMN regions which are also known to be important for memory fuction.
Li, X., Kehoe, E. G., McGinnity, TM., Coyle, D., & Bokde, A. (2015). Modulation of effective connectivity in the default mode network at rest and during a memory task. Brain Connectivity, 1. https://doi.org/10.1089/brain.2014.0249