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

Abstract

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.

Keywords: cognitive control; connectivity; default-mode; networks; reasoning; relational complexity.

Figure 1

Schematic of the WST and modified version used in the current study. a. In the classic WST participants are shown four cards (in this example, “3,” “8,” green and orange) and are provided with a conditional rule such as If a card shows an even number on one face, then its opposite face will be green. Participants are then asked which card(s) must be turned over to test the conditional rule provided. The only cards that can disconfirm the rule are the orange (reverse side even) and 8 (reverse side orange) cards. If the 3 card is orange on its opposite face it does not invalidate the rule (the rule does not say anything about odd cards). Likewise, if the reverse of the green card is an odd number the rule cannot be disconfirmed. b. Trial structure of the modified WST used in the functional magnetic resonance imaging (fMRI) study. Participants were presented with a rule (e.g., “If A then 7”), followed by a single “card,” and were then asked to judge if the presented card could disconfirm the rule. By presenting cards serially the level of relational complexity needed to disconfirm the rule is manipulated on a trial‐by‐trial basis. [Color figure can be viewed in the online issue, which is available at http://wileyonlinelibrary.com.]

Figure 2

Complexity‐based changes in regional activity. a. Average brain activity during card processing. The task‐positive contrast (average positive card minus null trials) showed significant neural activity in regions encompassing both frontoparietal and cingulo‐opercular networks [Dosenbach et al., 2010] (see Table 2 for details). The task‐negative contrast (null trials minus average positive card effect) showed brain regions that form part of the default‐mode network [Fox et al., 2005] (Table 2 ). b. Mean brain activity change with increases in card complexity in task‐positive and task‐negative contrasts. Error bars represent the standard error of the mean. Overall, task‐positive regions increased their activity as a function of card complexity. By contrast, task‐negative regions decreased their activity as a function of complexity. Note that these averaged results for the group were representative for all individual regions. [Color figure can be viewed in the online issue, which is available at http://wileyonlinelibrary.com.]

Figure 3

Complexity‐evoked changes in PPI connectivity. a. Red nodes correspond to task‐positive regions isolated in the general linear model analysis (Figure 2; see Table 2 for details). Blue nodes correspond to task‐negative (“deactivated”) regions. The red edges indicate increases in PPI connectivity between task‐positive regions, whereas the green edges represent increases in connectivity between task‐positive and task‐negative regions (details in Table 3). b. Changes in average PPI connectivity values between task‐positive and task‐negative regions as a function of increased card complexity. Average changes were representative of edge‐specific connectivity changes due to changes in complexity. [Color figure can be viewed in the online issue, which is available at http://wileyonlinelibrary.com.]

Figure 4

Complexity‐evoked changes in PPI connectivity within the default‐mode network. a. Purple edges indicate increased PPI connectivity as a function of complexity, whereas blue edges represent decreased connectivity (details in Table 4). b. Average PPI connectivity patterns for pairwise connections showing an increase in connectivity (in purple) and decreased connectivity (in blue) as a function of increased relational complexity. [Color figure can be viewed in the online issue, which is available at http://wileyonlinelibrary.com.]