Role of the Default Mode Network in Cognitive Transitions

Abstract

A frequently repeated finding is that the default mode network (DMN) shows activation decreases during externally focused tasks. This finding has led to an emphasis in DMN research on internally focused self-relevant thought processes. A recent study, in contrast, implicates the DMN in substantial externally focused task switches. Using functional magnetic resonance imaging, we scanned 24 participants performing a task switch experiment. Whilst replicating previous DMN task switch effects, we also found large DMN increases for brief rests as well as task restarts after rest. Our findings are difficult to explain using theories strictly linked to internal or self-directed cognition. In line with principal results from the literature, we suggest that the DMN encodes scene, episode or context, by integrating spatial, self-referential, and temporal information. Context representations are strong at rest, but rereference to context also occurs at major cognitive transitions.

Figure 1.

Task design. Participants were required to make same/different judgements on pairs of stimuli based on a task rule. Each task rule was cued by the frame color, learnt by participants in a training session prior to scanning. (a) Each of the 6 tasks and their associated frame color. There were 3 stimulus domains with 2 task rules associated with each. An additional black frame cued rest trials in which there was no upcoming task to complete. (b) Experimental design. Each trial consisted of a 2 s cue phase in which the colored frame specifying the task rule for the upcoming trial (or rest trial) was presented, followed by an execution phase (until response) or a 1.2 s delay, followed by a 1.75 s intertrial interval. “Cue-only trials” refer to task trials where there was no execution phase. The tasks were presented in a pseudorandom order creating 6 switch conditions: task stay trials (task trials preceded by the same task), within-domain switch (task trials preceded by same domain task trials), between-domain switch (task trials preceded by different domain task trials), rest switch (rest trials preceded by task trials), rest stay (rest trials preceded by rest trials), and restart (task trials preceded by rest trials).

Figure 2.

Regions of interest. (a) DMN ROIs from peak coordinates presented in Andrews-Hanna et al. (2010). (b) MD ROIs from Fedorenko et al. (2013).

Figure 3.

Contrasts of rest compared with task activity in each DMN subnetwork and the MD network. Significant (P < 0.05) increases in rest activity compared with task, as well as paired t-tests between contrasts within DMN subnetworks, are indicated with *P < 0.05, **P < 0.02, ***P < 0.01. Error bars show standard error of the mean across participants.

Figure 4.

Contrasts of between-domain switch, within-domain switch, restart and rest compared with task stay trials for each DMN subnetwork and MD regions. ((a) Core DMN, (b) MTL DMN, (c) dmPFC DMN, (d) MD). Significant (P < 0.05) increases in activity compared with task stay, as well as paired t-tests between contrasts within (sub)networks, are indicated with *P < 0.05, **P < 0.02, ***P < 0.01. Error bars show standard error of the mean across participants.

Figure 5.

Finite impulse response beta activity estimates in 1.1 s time bins during repeated rest trials before task restart for each DMN subnetwork and the MD network. ((a) Core DMN, (b) MTL DMN, (c) dmPFC DMN, (d) MD). Restart onset occurs at bin 19.

Figure 6.

Average classification accuracies minus chance for within-domain (light bars) and between-domain (dark bars) task pairs for each DMN subnetwork and the MD network. Significant classification accuracy above chance (P < 0.05), as well as significant paired t-tests between within-domain task pairs and between-domain task pairs, are indicated with *P < 0.05, **P < 0.02, ***P < 0.01. Error bars show standard error of the mean across participants.