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Modulation by task-difficulty in the default mode network varies with the complexity of perpetual information during decision making

Mohamed L. Seghier1*, Mohamed A. Fahim2, Oury Monchi3 and Claudine Habak2
  • 1 Emirates College for Advanced Education, Institute of Neurology, United Arab Emirates
  • 2 Emirates College for Advanced Education, United Arab Emirates
  • 3 University of Calgary, Canada

Introduction: Mind wandering is responsible for the lack of concentration in the classroom, which impacts on the level of comprehension and understanding by learners (Smallwood et al., 2007). However, mind wandering has also been shown to enhance creativity and problem solving skills (Leszczynski et al., 2017). It is thus important to understand the factors that modulate the interplay between the different brain networks that sustain mind wandering in order to minimize its behavioral costs and maximize its benefits. Many functional neuroimaging studies have shown that brain wandering simply reflects the brain being engaged in a different cognitive state, which involves a complex interplay between the default mode network (DMN) and other resting-state networks. Different DMN subregions are modulated by stimulus and task factors as well as by processing type (Andrews-Hanna, 2012; Seghier & Price, 2012). The amplitude of deactivation in DMN nodes can also be parametrically modulated by task difficulty (McKiernan et al., 2006; Singh & Fawcett, 2008) when participants are engaged in effortful external tasks. Here, we sought to examine how modulation of DMN activity by task difficulty is influenced by information complexity when manipulating low-level visual representations during perceptual decision making. Methods: fMRI data were collected in 20 healthy adults with a 3T Siemens scanner. Stimuli consisted of two Gabor patches presented side-by-side. Gabor patches consisted of a circular Gaussian window (envelope) multiplied with a sine-wave carrier. The carrier spatial frequency of one patch was randomly increased or decreased to generate four levels of spatial frequency difference, based on a behavioral psychophysics session. Levels of spatial frequency difference between the two patches (Weber Fractions) were set to yield correct responses of approximately 50, 75, 85 and 100% for each individual participant. These spatial frequency differences defined our four levels of discriminability (i.e. levels of task difficulty) ranging from very difficult (chance level) to very easy (100% correct). Complexity was controlled by changing the relative orientations: a same-orientation condition (‘same’), in which carrier orientation in each of the two patches was identical (fixed at vertical); and a different-oriented condition (‘diff’), in which carriers were oriented at 90° to each other (one vertical and one horizontal). Participants were asked to indicate which of the two patches contained the higher spatial frequency. More details about the paradigm can be found elsewhere (Habak et al., 2019). Data processing and statistical analyses were performed with SPM12 using standard procedures. Each trial onset was modelled as an event in condition-specific ‘stick-functions’ with a duration equal to the self-paced responses of each participant (Grinband et al., 2008). For each stimulus orientation, task difficulty was included as a single linear parametric modulator that was orthogonal to the main trial regressor. For the group analysis, contrast images of the parametric modulations by discriminability of our two stimulus orientation conditions (i.e. ‘same’ and ‘diff’), for each of the 20 participants’ first-level analyses, were entered into a second-level factorial analysis in SPM. Statistical comparisons are reported at p<0.05 FWE-corrected over the whole brain. Results: Levels of spatial frequency difference yielded matched accuracy and response times across orientation conditions. Activity modulation by discriminability, or difficulty (greater suppression), was significant in right inferior parietal lobule (IPL) for ‘same’ at p<0.05 corrected (+52 -70 +28, Z=5.2). For ‘diff’, no voxels survived a corrected level, but a similar effect in right IPL was observed at a lower threshold (Z=3.8). There was a trend (Z=1.5) for stronger modulation by discriminability/difficulty in the right IPL when orientations were the same (‘same’) than when they differed (‘diff’). At uncorrected levels (p<0.001), modulation by difficulty was also seen in left IPL for both orientations, along with posterior cingulate cortex and medial frontal cortex for ‘same’ and ‘diff’ orientations, respectively. Discussion and Conclusion: The strongest activity modulation by task difficulty was observed in the right IPL (Benedek et al., 2014; Shulman et al., 2007), but the size of this modulation varied with task complexity. The significant effect of representational complexity (Murphy et al., 2018) for perceptual information (i.e. ‘same’ vs ‘diff’ orientations) calls for better definitions of ‘task demands’ and ‘task load’ (Forster & Lavie, 2009), which are typically equated with ‘task difficulty’, when looking at the modulation of DMN activity in healthy or clinical populations. In addition, our findings have implications for educational settings regarding the way in which perceptual information is typically presented during learning.

References

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Keywords: Default Mode Network, task difficulty, task complexity, perceptual decision making, functional MRI (fMRI)

Conference: 4th International Conference on Educational Neuroscience, Abu Dhabi, United Arab Emirates, 10 Mar - 11 Mar, 2019.

Presentation Type: Poster Presentation

Topic: Educational Neuroscience

Citation: Seghier ML, Fahim MA, Monchi O and Habak C (2019). Modulation by task-difficulty in the default mode network varies with the complexity of perpetual information during decision making. Conference Abstract: 4th International Conference on Educational Neuroscience. doi: 10.3389/conf.fnhum.2019.229.00004

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Received: 03 Mar 2019; Published Online: 27 Sep 2019.

* Correspondence: Dr. Mohamed L Seghier, Emirates College for Advanced Education, Institute of Neurology, Abu Dhabi, WC1N 3BG, United Arab Emirates, mseghier@gmail.com