Abstract
The hypothesis of a default mode network (DMN) of brain function is based on observations of task-independent decreases of brain activity during effort as participants are engaged in tasks in contrast to resting. On the other hand, studies also showed that DMN regions activate rather than deactivate in response to task-related events. Thus, does DMN “deactivate” during effort as compared to resting? We hypothesized that, with high-frequency event-related signals removed, the task-residual activities of the DMN would decrease as compared to resting. We addressed this hypothesis with two approaches. First, we examined DMN activities during resting, task residuals, and task conditions in the stop signal task using independent component analysis (ICA). Second, we compared the fractional amplitude of low-frequency fluctuation (fALFF) signals of DMN in resting, task residuals, and task data. In the results of ICA of 76 subjects, the precuneus and posterior cingulate cortex (PCC) showed increased activation during task as compared to resting and task residuals, indicating DMN responses to task events. Precuneus but not the PCC showed decreased activity during task residual as compared to resting. The latter finding was mirrored by fALFF, which is decreased in the precuneus during task residuals, as compared to resting and task. These results suggested that the low-frequency blood oxygen level-dependent signals of the precuneus may represent a useful index of effort during cognitive performance.
Highlights
Consistent with this hypothesis, our findings suggest that taskresidual plays an important role in task engagement
Identification of task residual signals helps elucidate changes in spontaneous activity of the default mode network (DMN), which may represent a neural signature of effort during cognitive performance
The precuneus that we identified as the neural surrogate of effort is within the dorsal part of the medial posterior parietal cortex
Summary
There is growing evidence from functional imaging that neural activity during a state of “resting” represents an intrinsic baseline in the default mode network (DMN), including the posterior cingulate cortex (PCC), precuneus, medial prefrontal cortex (MPFC), and inferior parietal lobule (IPL; Gusnard et al, 2001a,b; Raichle et al, 2001; Greicius et al, 2003; Fransson, 2005, 2006; Damoiseaux et al, 2006; Fox and Raichle, 2007; Buckner et al, 2008). This DMN activity is often referred to as task-induced deactivation (TID) because the regions appear deactivated on a cognitive task. TIDs in several of the default mode regions varied parametrically as a function of task difficulty (McKiernan et al, 2003). Fransson (2006) showed that spontaneous signal fluctuations in the DMN persist and reorganize in response to changes in external work load
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