The default network and self-generated thought: component processes, dynamic control, and clinical relevance

Mind your thoughts: associations between self-generated thoughts and stress-induced and baseline levels of cortisol and alpha-amylase

Stress is a major health burden in today's society. Research shows that negative cognitive styles are associated with increased stress reactivity, low mood and accelerated cellular aging. Our study sought to unravel the relationship between the content of self-generated thoughts and psychosocial stress measured in terms of hypothalamic-pituitary-adrenal axis and sympathetic activity. Features of self-generated thoughts were assessed using thought sampling while participants performed cognitive tasks following a stress induction or in a baseline condition. More negatively toned emotional thoughts and more social temporal thoughts with a past focus were associated with increased cortisol and alpha-amylase levels, both after stress and at baseline. More social temporal thoughts with a future focus, on the other hand, had an overall attenuating effect on the levels of both stress markers. Our results indicate a fundamental link between the thoughts and stress levels we experience. Understanding the mechanisms governing this mind-body association may have important implications for understanding and counteracting the high incidence of stress-related disorders in today's society.

What we talk about when we talk about the default mode network

The default mode network (DMN) has been widely defined as a set of brain regions that are engaged when people are in a “resting state” (left to themselves in a scanner, with no explicit task instruction). The network emerged as a scientific object in the early twenty-first century, and in just over a decade has become the focus of intense empirical and conceptual neuroscientific inquiry. In this Perspective, we contribute to the work of critical neuroscience by providing brief reflections on the birth, working life, and future of the DMN. We consider: how the DMN emerged through the convergence of distinct lines of scientific investigation; controversies surrounding the definition, function and localization of the DMN; and the lines of interdisciplinary investigation that the DMN has helped to enable. We conclude by arguing that one of the most pressing issues in the field in 2014 is to understand how the mechanisms of thought are related to the function of brain dynamics. While the DMN has been central in allowing the field to reach this point, it is not inevitable that the DMN itself will remain at the heart of future investigations of this complex problem.

Distracted and down: neural mechanisms of affective interference in subclinical depression

Previous studies have shown that depressed individuals have difficulty directing attention away from negative distractors, a phenomenon known as affective interference. However, findings are mixed regarding the neural mechanisms and network dynamics of affective interference. The present study addressed these issues by comparing neural activation during emotion-word and color-word Stroop tasks in participants with varying levels of (primarily subclinical) depression. Depressive symptoms predicted increased activation to negative distractors in areas of dorsal anterior cingulate cortex (dACC) and posterior cingulate cortex (PCC), regions implicated in cognitive control and internally directed attention, respectively. Increased dACC activity was also observed in the group-average response to incongruent distractors, suggesting that dACC activity during affective interference is related to overtaxed cognitive control. In contrast, regions of PCC were deactivated across the group in response to incongruent distractors, suggesting that PCC activity during affective interference represents task-independent processing. A psychophysiological interaction emerged in which higher depression predicted more positively correlated activity between dACC and PCC during affective interference, i.e. greater connectivity between cognitive control and internal-attention systems. These findings suggest that, when individuals high in depression are confronted by negative material, increased attention to internal thoughts and difficulty shifting resources to the external world interfere with goal-directed behavior.

Self-generated thoughts and depression: from daydreaming to depressive symptoms

Human minds often engage in thoughts and feelings that are self-generated rather than stimulus-dependent, such as daydreaming. Recent research suggests that under certain circumstances, daydreaming is associated with adverse effects on cognition and affect. Based on recent literature about the influence of resting mind in relation to rumination and depression, this questionnaire study investigated mechanisms linking daydreaming to depressive symptoms. Specifically, an indirect effect model was tested in which daydreaming influences depressive symptoms through enhancing self-focus and ruminative thought. Results were in line with the hypothesis and several alternative pathways were ruled out. The results provide initial supportive evidence that daydreaming can influence depressive symptoms through influences on self-focus and rumination. Further research should use prospective or experimental designs to further validate and strengthen these conclusions.

Contextual and perceptual brain processes underlying moral cognition: a quantitative meta-analysis of moral reasoning and moral emotions

Background and Objectives

Human morality has been investigated using a variety of tasks ranging from judgments of hypothetical dilemmas to viewing morally salient stimuli. These experiments have provided insight into neural correlates of moral judgments and emotions, yet these approaches reveal important differences in moral cognition. Moral reasoning tasks require active deliberation while moral emotion tasks involve the perception of stimuli with moral implications. We examined convergent and divergent brain activity associated with these experimental paradigms taking a quantitative meta-analytic approach.

Data Source

A systematic search of the literature yielded 40 studies. Studies involving explicit decisions in a moral situation were categorized as active (n = 22); studies evoking moral emotions were categorized as passive (n = 18). We conducted a coordinate-based meta-analysis using the Activation Likelihood Estimation to determine reliable patterns of brain activity.

Results & Conclusions

Results revealed a convergent pattern of reliable brain activity for both task categories in regions of the default network, consistent with the social and contextual information processes supported by this brain network. Active tasks revealed more reliable activity in the temporoparietal junction, angular gyrus and temporal pole. Active tasks demand deliberative reasoning and may disproportionately involve the retrieval of social knowledge from memory, mental state attribution, and construction of the context through associative processes. In contrast, passive tasks reliably engaged regions associated with visual and emotional information processing, including lingual gyrus and the amygdala. A laterality effect was observed in dorsomedial prefrontal cortex, with active tasks engaging the left, and passive tasks engaging the right. While overlapping activity patterns suggest a shared neural network for both tasks, differential activity suggests that processing of moral input is affected by task demands. The results provide novel insight into distinct features of moral cognition, including the generation of moral context through associative processes and the perceptual detection of moral salience.

Contributions of episodic retrieval and mentalizing to autobiographical thought: evidence from functional neuroimaging, resting-state connectivity, and fMRI meta-analyses

A growing number of studies suggest the brain's "default network" becomes engaged when individuals recall their personal past or simulate their future. Recent reports of heterogeneity within the network raise the possibility that these autobiographical processes comprised of multiple component processes, each supported by distinct functional-anatomic subsystems. We previously hypothesized that a medial temporal subsystem contributes to autobiographical memory and future thought by enabling individuals to retrieve prior information and bind this information into a mental scene. Conversely, a dorsal medial subsystem was proposed to support social-reflective aspects of autobiographical thought, allowing individuals to reflect on the mental states of one's self and others (i.e. "mentalizing"). To test these hypotheses, we first examined activity in the default network subsystems as participants performed two commonly employed tasks of episodic retrieval and mentalizing. In a subset of participants, relationships among task-evoked regions were examined at rest, in the absence of an overt task. Finally, large-scale fMRI meta-analyses were conducted to identify brain regions that most strongly predicted the presence of episodic retrieval and mentalizing, and these results were compared to meta-analyses of autobiographical tasks. Across studies, laboratory-based episodic retrieval tasks were preferentially linked to the medial temporal subsystem, while mentalizing tasks were preferentially linked to the dorsal medial subsystem. In turn, autobiographical tasks engaged aspects of both subsystems. These results suggest the default network is a heterogeneous brain system whose subsystems support distinct component processes of autobiographical thought.