Interactions between default mode and control networks as a function of increasing cognitive reasoning complexity

Successful performance of challenging cognitive tasks depends on a consistent functional segregation of activity within the default‐mode network, on the one hand, and control networks encompassing frontoparietal and cingulo‐opercular areas on the other. Recent work, however, has suggested that in some cognitive control contexts nodes within the default‐mode and control networks may actually cooperate to achieve optimal task performance. Here, we used functional magnetic resonance imaging to examine whether the ability to relate variables while solving a cognitive reasoning problem involves transient increases in connectivity between default‐mode and control regions. Participants performed a modified version of the classic Wason selection task, in which the number of variables to be related is systematically varied across trials. As expected, areas within the default‐mode network showed a parametric deactivation with increases in relational complexity, compared with neural activity in null trials. Critically, some of these areas also showed enhanced connectivity with task‐positive control regions. Specifically, task‐based connectivity between the striatum and the angular gyri, and between the thalamus and right temporal pole, increased as a function of relational complexity. These findings challenge the notion that functional segregation between regions within default‐mode and control networks invariably support cognitive task performance, and reveal previously unknown roles for the striatum and thalamus in managing network dynamics during cognitive reasoning. Hum Brain Mapp 36:2719–2731, 2015 . © 2015 Wiley Periodicals, Inc .