Kalina Christoff

Thoughts are pervasive in our conscious experience, arising from sources of deliberate intention, habitual pattern, or even out of the blue. Thoughts of the lattermost category, referred to as spontaneous thoughts, have become the subject of a growing number of experimental investigations. An aspect of spontaneous thought that has remained difficult to study is the neural mechanisms supporting their initial generation. This is largely due to how the generation of spontaneous thoughts is neither deliberate nor conscious, making it difficult to collect self-report data as to their timing. However, past research has shown it is possible to use self-reports about the conscious onset of spontaneous thoughts as a benchmark for analyzing neural activations in the time before their conscious onset. This depends, however, on participants being able to report on a thought’s arising both quickly and accurately. Experienced mindfulness meditators have proven a useful participant sample to use when conducting such research, given their extensive practice in noting the arising of subtle mental events into conscious experience. Picking up where previous research left off, the present thesis examined the neural correlates of spontaneous thought by combining self-reports made by a sample of experienced mindfulness meditators with neural measurements collected via fMRI. Participants were instructed to report on the initial arising of spontaneous thoughts into their conscious experience, allowing us to analyze neural activations in the time leading up to their reports when the mechanisms supporting thought generation are believed to unfold. Unlike previous research, we did not observe neural activation associated with generation in the time leading up to participants self-reports. We instead observed widespread neural activation across brain systems involved in task monitoring, decision making, action planning, and semantic processing. These results suggest participants may have had difficulty reporting on the arising of spontaneous thoughts and thus relied upon semantic decision-making to evaluate their experience more rigorously. This raises the possibility that information about internal states, like thoughts, is at least partially stored as semantic knowledge. Our findings also provide important methodological guidelines to consider in future research examining the onset of subtle mental events.

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Spontaneous thought refers to a mental state, or series of mental states, that are unconstrained by a specific task and move freely over time. Converging evidence suggests that spontaneous thoughts may contain mental imagery of scenes ('scene construction') when remembering the past and imagining the future ('mental time travel'). However, no research has directly examined the relationship between scene construction and mental time travel during spontaneous thought. We used experience sampling and multi-level modeling to obtain subjective reports from eighty participants during waking rest, and examined these reports along three dimensions: (1) freedom of movement (referring to the degree to which thoughts are deliberate or spontaneous), (2) mental imagery (including scene construction, inner speech, and isolated elements), and (3) temporal orientation (towards the past, present, and future). Our results showed that multiple types of mental imagery, including scene construction, inner speech, and isolated elements, were positively associated with spontaneous thoughts generated during waking rest. Furthermore, all forms of mental imagery were positively associated with past and future orientation. In contrast, deliberate thoughts generated during waking rest were negatively associated with mental imagery and present orientation. These data suggest that various forms of mental imagery, including scene construction, inner speech, and isolated elements, all support spontaneous thoughts of the past and future. This research advances our understanding of healthy, adaptive human thought patterns in everyday life, and provides a baseline for better understanding unhealthy, maladaptive thought patterns in clinical contexts.

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Freedom-of-movement in thought (the degree to which thought is constrained in its variety as opposed to being free to change) can be empirically dissociated from other well-studied dimensions of thought such as its task-unrelatedness in everyday life setting, but has yet to be studied in a controlled experimental environment. While there are several proposed mechanisms by which thought can become constrained (and therefore less freely moving), none have bene explored empirically. The present study set out to uncover which constructs associated with thought’s task-relatedness were also related to its freedom-of-movement and to test potential mechanisms of constraint. Motivation was within-subjects through a variable-value time-sensitive task and administered experience sampling probes asking participants to self-report the level of freely-moving thought, task-unrelated thought, deliberate control, arousal, and valence they were experiencing. Electrodermal activity and pupillometry were used as an index of physiological arousal in addition to self-reports. When participants were more highly motivated they reported having more constrained and more task-related thoughts, and having greater control over their thoughts. Control fully mediated motivation’s impact on freedom-of-movement of thought, but only partially mediated motivation’s impact on task-unrelated thought. Neither self-report or physiological measures of arousal were impacted by the manipulation, but high levels of both task-unrelated and freely-moving thought were associated with high ratings or self-reported arousal, higher pupillary responses to stimuli and smaller average pupil size, with freely-moving thought being uniquely associated with reduced skin conductance. Additionally, high freely-moving thought ratings were uniquely associated with slower responses, while high task-unrelated thought ratings were uniquely associated with low valence ratings. Overall, these findings support and further extend the previously identified dissociation between task-unrelatedness and freedom-of-movement as two separable dimensions of thought. They indicate that a person’s degree of control over their own thoughts is a crucial determinant of the content and especially the dynamics of that thought, but further work needs to be done to explore what nonconscious factors constrain thought movement.

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The accuracy of subjective reports, especially those involving introspection of one’s own internal processes, remains unclear, and research has demonstrated large individual differences in introspective accuracy. It has been hypothesized that introspective accuracy may be heightened in persons who engage in meditation practices, due to the highly introspective nature of such practices. We undertook a preliminary exploration of this hypothesis, examining introspective accuracy in a cross-section of meditation practitioners (1 - 15,000 hrs experience). Expert meditators showed significantly better introspective accuracy than novices; overall meditation experience also significantly predicted individual introspective accuracy. We then undertook a neuroimaging study (with a partially overlapping sample of meditators) to investigate possible structural brain differences between long-term meditators with high introspective accuracy, and meditation-naïve control subjects. Using magnetic resonance imaging to acquire 3D anatomical brain images, we used voxel-based morphometry to assess grey matter concentration differences between groups, and also as a function of meditation experience. Between-groups results suggest significantly greater concentrations of grey matter in primary somatosensory cortex in long-term meditators vs. controls; among meditators, grey matter concentration was found to increase in several regions key to body-awareness with increasing experience in the body-scanning meditation practice.

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Our capacity for self-control is supported by the use of behaviour-guiding rules. A fundamental question is how we decide which one of out of many potential rules to follow. If different rules were integrated with their expected reward-value, they could be compared, and the one with the highest value selected. However, it currently remains unknown whether any areas of the brain perform this integrative function. To address this question, we took advantage of functional magnetic resonance imaging (fMRI)-adaptation—the ubiquitous finding that repeated as compared to novel stimuli elicit a change in the magnitude of neural activity in areas of the brain that are sensitive to that stimulus. We created a novel fMRI-adaptation paradigm in which instruction cues signaled novel or repeated task-rules and expected rewards. We found that the inferior frontal sulcus (IFS)—a sub-region of the lateral prefrontal cortex—exhibited fMRI-adaptation uniquely when both rule and reward information repeated as compared to when it was novel. fMRI-adaptation was not observed when either factor repeated in isolation, providing strong evidence that the IFS supports an integrated representation of task-rules and rewards. Consistent with an integrative role, the IFS exhibited correlated activity with numerous rule-related and reward-related areas of the brain across the entire experimental time-course. Additionally, the correlation strength between the IFS and a subset of these regions changed as a function of the novelty of rule and reward information presented during the instruction cue period. Our results provide novel evidence that the IFS integrates rules with their expected reward-value, which in turn can guide complex decision making.

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Creativity is most often defined as the ability to produce ideas that are both novel and useful. Consistent with this twofold definition, psychological theories have suggested that creativity involves a twofold process characterized by a generative (or associative) component that facilitates the production of novel ideas, and an evaluative (or analytic) component that enables the assessment of these ideas as to their usefulness. To investigate this, the present study employed a novel paradigm that was specifically designed to allow for separately examining the generative and evaluative components of the creative process. Functional magnetic resonance imaging (fMRI) was used to identify the contribution of particular brain regions to creative generation and evaluation. Participants were presented with short book descriptions and, using an fMRI-compatible drawing tablet, designed corresponding book cover illustrations while alternating between the generation and evaluation of ideas. Creative generation and evaluation were associated with recruitment of distinct neural circuits, with generation preferentially recruiting medial temporal lobe regions, and evaluation showing joint recruitment of executive and default network regions. These findings suggest that the medial temporal lobe may play an important role in the generation of novel ideas, and that creative evaluation may extend beyond deliberate and cognitive analytical processes supported by executive resources to include spontaneous, affective, and visceroceptive analytical processes. In summary, separating and alternating between generative and evaluative modes during a creative task helped to provide a better characterization of the contributions of creativity-related brain areas to the creative process, which had previously only been inferred indirectly. The results of this study suggest that creative thinking recruits a unique configuration of neural processes not typically used together in more traditional tasks.

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In real-time fMRI regulation studies, subjects view feedback showing the fluctuating activation within a particular region of their brains as they attempt to regulate that region’s activation. This technology is of theoretical and clinical interest; however, it is unclear whether real-time regulation training is equally effective for all brain regions. Real-time feedback can be positive (if activation is in the desired direction) or negative (if in the opposite direction), suggesting a potential confound for training studies. We reasoned that if particular brain regions are differentially activated according to feedback valence, activations related to feedback might interact with the regulation task. Thus, we designed a study that allowed us to manipulate the valence of feedback in a real-time training context. Subjects were instructed to up-regulate and down-regulate their parahippocampal place area (PPA) in 30-second blocks while in the scanner, viewing feedback which they believed to reflect the activation of this region. In reality, the feedback was pre-constructed, and alternated between positive and negative valence blocks of varying length. Comparing positive with negative feedback, positive feedback activated nucleus accumbens, a reward centre, and certain emotion-relevant regions. Negative feedback produced little consistent activation over positive feedback. In general, feedback effects were greater for moderate feedback than strong feedback, possibly reflecting heightened uncertainty toward moderate feedback. We conclude that feedback-based activations are unlikely to interfere with regulation training for most cortical regions, though emotion-relevant regions may be more sensitive to feedback valence. We also propose that researchers explore feedback methods which emphasize reward-based learning.

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