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THE NEUROANATOMICAL SUBSTRATES OF MIND-WANDERING
Mind wandering is a ubiquitous phenomenon of our mental life that is related to perceptual decoupling of the immediate external environment. In another words, mindwandering episodes disconnect the perception of external stimulus events in a regular and periodic way (Kam & Handy, 2013). Thus in the cognitive neuroscience has been growing an big interest in understanding the impact of this perceptual decoupling related to mind wandering in the processing to stimuli in the external environment (Barron et al., 2011; O’Connell et al., 2009; Smallwood et al., 2008; Stawarczyk, Majerus, Maquet, & D’argembeau, 2011). Mind wandering is now being recognized as a new expresion of attentional selection, due to this specific feature to disconnected the attention the outside world, such that we no longer select the external stimuli for sensory processing. Therefore, in the last few decades, great progress has been made in the understanding of the neural underpinnings of spatial attention related to mind wandering. In humans, functional MRI (fMRI) has revealed that spatial attention is comprised of two fronto-parietal attention networks (Corbetta, Patel, & Shulman, 2008; Corbetta & Shulman, 2002). A dorsal attentional network (DAN) includes the intra-parietal sulcus (IPS)/superior parietal lobule and the frontal eye field (FEF)/dorsolateral prefrontal cortex. The ventral attention network (VAN) comprises the temporal-parietal junction (TPJ) and the ventral prefrontal region (inferior and middle frontal gyrus). Importantly, the DAN is thought to be bilateral and symmetric, whereas the VAN is strongly lateralized to the right hemisphere (Corbetta et al., 2008). These fMRI results are based on variants of the classic Posner location-cueing paradigm (Posner, Walker, Friedrich, & Rafal, 1984), often used in the study of spatial attention. In this paradigm, the presentation of a visual target is preceded by a cue, and participants are required to respond to the target and not to the cue (which can or cannot be predictive of one or more of the targets features).
It is also important to highlight, that the DAN is active during the orienting period between cue and target, while the VAN shows an increase response when participants have to respond to uncued (and thereby sometimes unexpected) targets (Corbetta et al., 2008). (Figure 4).
Default mode network and mind-wandering
In the last decade, one of the focuses of interest for neuroscientists have been study the human brain intrinsic properties to generate and sustain an internal stream of thoughts unrelated to the external world specifically the interest has focused on the neuroanatomy related to mind-wandering. Prior studies have reported increased activity in a coordinated system of brain regions, later dubbed as the “default mode network” (DMN), occurring when individuals do not have to perform demanding perceptual tasks (Raichle et al., 2001).
The brain areas of this network include the ventral medial prefrontal cortex (vMPFC), the posterior cingulate cortex (PCC), the inferior parietal lobule (IPL), the dorsal medial prefrontal cortex (dMPFC), and the hippocampal formation (HF) (for a review see Buckner, Andrews-Hanna, & Schacter, 2008). Evidence also suggests that the DMN is a coherent system, because this set of brain regions shows an intrinsic functional correlation between each other, and are connected via direct and indirect anatomic projections.
Therefore two subsystems, organized as hubs of functional conection, have been proposed within the DMN: 1) the PCC, and 2) the MPFC. Moreover, the dMPFC and HF are also both correlated with other regions of the DMN. It is suggested that the HF and dMPFC are two distinct subsystems connected to the two hubs of a larger DMN (Buckner et al., 2008). However, despite the DMN being associated with stimulus-independent thoughts (Buckner et al., 2008), it is still not clear the specific role of DMN during mind-wandering. This is probably because DMN activity cannot be attributed solely to spontaneous thought (Raichle, 2009; Raichle & Snyder, 2007). For instance, seizure episodes in epileptic patients also coincide with a sudden increase in the activity of the DMN, suggesting a possible link between this network and the onset of crises (Broyd et al., 2009; Ossandon et al., 2011).
Furthermore, spontaneous activity measured with blood oxygen level-dependent (BOLD) during fMRI in the resting awake or anesthetized brain, is organized in multiple highly specific functional anatomical networks, called resting state networks, RSNs (Biswal et al., 2010; Mantini, Perrucci, Del Gratta, Romani, & Corbetta, 2007). These RSNs show fluctuations at frequencies between 0.01 and 0.1 Hz, and exhibit strong patterns of coherence within known brain systems (Raichle & Snyder, 2007). For example, it has been shown that RSNs patterns have a similar anatomical connectivity in both the animal (Vincent et al., 2007) and human brain (Zhang et al., 2008).
BEHAVIORAL AND NEURAL CORRELATES OF SENSORY ATTENUATION: AN ERP STUDY OF NEURAL EVENTS LEADING TO MIND WANDERING.
Spontaneous attenuation of sensory processing in the human brain substantially contributes to attentional decoupling, which results in mind-wandering experience. However, it is not clear how this sensory attenuation develops in time. Here, we used a continuous attentional assessment during a visual discrimination task, and addressed the electrophysiological correlates of the dynamics of these phenomena. We described modulations of components related to early visual processing shortly before participants reported mind-wandering episodes. The enhancement of P1 prior to mind-wandering reports, as compared to on-task conditions, might reflect the absence of suppression of unattended stimuli, related to alertness activity. The N1 modulation suggests decreased neural resources during mind wandering related with the early visual processing of the sensory input. Mind wandering also increased the amplitude of a late component peaking around 300-500 ms, perhaps because of increased response preparation. Thus, early, abrupt sensory attenuation appears to be strongly linked to the mind-wandering phenomenon. Keywords: ERP, attentional decoupling, sensory attenuation, thought sampling questions.
EEG data acquisition and preprocessing.
EEG was acquired using a 128-channel HydroCel Geodesic Sensor Net of 129 Ag/AgCl electrodes (Electrical Geodesics, Inc.-EGI system, Eugene, OR, USA). All electrodes impedances were kept below 50 kΩ (Ferree, Luu, Russell, & Tucker, 2001), and the signal was re-referenced to the Cz electrode. The raw EEG signal was filtered on-line using a 0.1 Hz highpass filter, digitized with a sampling rate of 1000 Hz, and sub-sampled to 250 Hz. ERP data were filtered off-line using a 0.1-30 Hz bandpass filter. Data were then segmented into 700 ms epochs (-100 to 600 ms), and baseline was corrected at -100 with respect to stimulus onset, which were sorted by trial type response (for target and nontarget letters categorized as off-task or on-task conditions) before to presentation of the TSQ.
Table of contents :
ABSTRACT
ACKNOWLEDGEMENTS
TABLE OF CONTENTS
TABLE OF FIGURES
CHAPTER 1. LITERATURE REVIEW
INTRODUCTION
1.1. MIND WANDERING: CONCEPTUAL AND THEORETICAL ISSUES
1.1.1. Theoretical framework of mind-wandering
1.1.2. Terminology of mind-wandering
1.2. STUDY OF BRAIN SIGNALS WITH ELECTROENCEPHALOGRAPHY (EEG).
1.2.1. Event-related potentials
1.3. EXPERIMENTAL METHODS TO STUDY MIND-WANDERING
1.3.1. Neurophenomenological measures
1.3.2. Behavioral measures
1.3.3. Neurocognitive measures
1.4. THE NEUROANATOMICAL SUBSTRATES OF MIND-WANDERING
1.4.1. Dorsal and ventral attention networks
1.4.2. Default mode network and mind-wandering
1.5. TOWARD FINDING THE NEURAL CORRELATES OF MIND-WANDERING
1.5.1. Task-evoked responses and mind-wandering
1.5.2. Brain rhythms and mind-wandering
CHAPTER 2. OUTSTANDING QUESTIONS
2.1. AIMS OF THE THESIS
CHAPTER 3. EXPERIMENTAL CONTRIBUTION.
INTRODUCTION TO THE FIRST ARTICLE
3.1. FLUCTUATING MIND: SPONTANEOUS PSYCHOPHYSICAL VARIABILITY DURING MIND-WANDERING
3.1.1. Abstract
3.1.2. Introduction
3.1.3. Materials and methods.
3.1.4. Results
3.1.5. Discussion
3.1.6. Author Contributions
3.1.7. References
INTRODUCTION TO THE SECOND ARTICLE
3.2. BEHAVIORAL AND NEURAL CORRELATES OF SENSORY ATTENUATION: AN ERP STUDY OF NEURAL EVENTS LEADING TO MIND WANDERING.
3.2.1. Abstract
3.2.2. Introduction
3.2.3. Materials and methods
3.2.4. Results
3.2.5. Discussion
3.2.6. Author contributions
3.2.7. References
CHAPTER 4. GENERAL DISCUSSION AND CONCLUSION
4.1. GENERAL DISCUSSION.
4.1.1. Synthesis of the main results
4.1.2. Behavioral variability of mind wandering.
4.1.3. Neural correlates of mind wandering
4.1.4. Mind wandering and executive control.
4.1.5. Mind wandering and attentional regulation
4.1.6. Mind wandering and the information processing model
4.2. LIMITATIONS AND PERSPECTIVES FOR FUTURE RESEARCH.
4.2.1. General limitations.
4.2.2. Implications for future research.
4.3. CONCLUSIONS
GENERAL REFERENCES.
