Individual variation in patterns of task focused, and detailed, thought are uniquely associated within the architecture of the medial temporal lobe

Understanding the neural processes that support different patterns of ongoing thought is an important goal of contemporary cognitive neuroscience. Early accounts assumed the default mode network (DMN) was especially important for conscious attention to task-irrelevant/personally relevant material. However, simple task-negative accounts of the DMN are incompatible with more recent evidence that neural patterns within the system can be related to ongoing processing during active task states. To better characterize the contribution of the DMN to ongoing thought, we conducted a cross-sectional analysis of the relationship between the structural organisation of the brain, as indexed by cortical thickness, and patterns of experience, identified using experience sampling in the cognitive laboratory. In a sample of 181 healthy individuals (mean age 20 years, 117 females) we identified an association between cortical thickness in the anterior parahippocampus and patterns of task focused thought, as well as an adjacent posterior region in which cortical thickness was associated with experiences with higher levels of subjective detail. Both regions fell within regions of medial temporal lobe associated with the DMN, yet varied in their functional connectivity: the time series of signals in the ‘on-task’ region were more correlated with systems important for external task-relevant processing (as determined by meta-analysis) including the dorsal and ventral attention, and fronto-parietal networks. In contrast, connectivity within the region linked to subjective ‘detail’ was more correlated with the medial core of the DMN (posterior cingulate and the medial pre-frontal cortex) and regions of primary visual cortex. These results provide cross-sectional evidence that confirms a role of the DMN in how detailed experiences are and so provide further evidence that the role of this system in experience is not simply task-irrelevant. Our results also highlight processes within the medial temporal lobe, and their interactions with other regions of cortex as important in determining multiple aspects of how human cognition unfolds

Neurocognitive patterns dissociating semantic processing from executive control are linked to more detailed off-task mental time travel

Features of ongoing experience are common across individuals and cultures. However, certain people express specific patterns of thought to a greater extent than others. Contemporary psychological theory assumes that individual differences in thought patterns occur because different types of experience depend on the expression of different neurocognitive processes. Consequently, individual variation in the underlying neurocognitive architecture is hypothesised to determine the ease with which certain thought patterns are generated or maintained. Our study (N = 178) tested this hypothesis using multivariate pattern analysis to infer shared variance among measures of cognitive function and neural organisation and examined whether these latent variables explained reports of the patterns of on-going thoughts people experienced in the lab. We found that relatively better performance on tasks relying primarily on semantic knowledge, rather than executive control, was linked to a neural functional organisation associated, via meta-analysis, with task labels related to semantic associations (sentence processing, reading and verbal semantics). Variability of this functional mode predicted significant individual variation in the types of thoughts that individuals experienced in the laboratory: neurocognitive patterns linked to better performance at tasks that required guidance from semantic representation, rather than those dependent on executive control, were associated with patterns of thought characterised by greater subjective detail and a focus on time periods other than the here and now. These relationships were consistent across different days and did not vary with level of task demands, indicating they are relatively stable features of an individual’s cognitive profile. Together these data confirm that individual variation in aspects of ongoing experience can be inferred from hidden neurocognitive architecture and demonstrate that performance trade-offs between executive control and long-term semantic knowledge are linked to a person’s tendency to imagine situations that transcend the here and now

Missing the forest because of the trees : Slower alternations during binocular rivalry are associated with lower levels of visual detail during ongoing thought

Conscious awareness of the world fluctuates, either through variation in how vividly we perceive the environment, or when our attentional focus shifts away from information in the external environment towards information that we generate via imagination. Our study combined individual differences in experience sampling, psychophysical reports of perception, and neuroimaging descriptions of structural connectivity to better understand these changes in conscious awareness. In particular, we examined (1) whether aspects of ongoing thought—indexed via multi-dimensional experience sampling during a sustained-attention task—are associated with the white-matter fibre organization of the cortex as reflected by their relative degree of anisotropic diffusion, and (2) whether these neuro-cognitive descriptions of ongoing experience are related to a more constrained measure of visual consciousness through analysis of bi-stable perception during binocular rivalry. Individuals with greater fractional anisotropy in right hemisphere white-matter regions involving the inferior fronto-occipital fasciculus, the superior longitudinal fasciculus, and the cortico-spinal tract, described their ongoing thoughts as lacking external details. Subsequent analysis indicated that the combination of low fractional anisotropy in these right hemisphere regions, with reports of thoughts with high-levels of external details, was associated with the shortest periods of dominance during binocular rivalry. Since variation in binocular rivalry reflects differences between bottom-up and top-down influences on vision, our study suggests that reports of ongoing thoughts with vivid external details may occur when conscious precedence is given to bottom-up representation of perceptual information

Facing up to the wandering mind: Patterns of off-task laboratory thought are associated with stronger neural recruitment of right fusiform cortex while processing facial stimuli.

Human cognition is not always tethered to events in the external world. Laboratory and real world experience sampling studies reveal that attention is often devoted to self-generated mental content rather than to events taking place in the immediate environment. Recent studies have begun to explicitly examine the consistency between states of off-task thought in the laboratory and in daily life, highlighting differences in the psychological correlates of these states across the two contexts. Our study used neuroimaging to further understand the generalizability of off-task thought across laboratory and daily life contexts. We examined (1) whether context (daily life versus laboratory) impacts on individuals' off-task thought patterns and whether individual variations in these patterns are correlated across contexts; (2) whether neural correlates for the patterns of off-task thoughts in the laboratory show similarities with those thoughts in daily life, in particular, whether differences in cortical grey matter associated with detail and off-task thoughts in the para-hippocampus, identified in a prior study on laboratory thoughts, were apparent in real life thought patterns. We also measured neural responses to common real-world stimuli (faces and scenes) and examined how neural responses to these stimuli were related to experiences in the laboratory and in daily life - finding evidence of both similarities and differences. There were consistent patterns of off-task thoughts reported across the two contexts, and both patterns had a commensurate relationship with medial temporal lobe architecture. However, compared to real world off-task thoughts, those in the laboratory focused more on social content and showed a stronger correlation with neural activity when viewing faces compared to scenes. Overall our results show that off-task thought patterns have broad similarities in the laboratory and in daily life, and the apparent differences may be, in part, driven by the richer environmental context in the real world. More generally, our findings are broadly consistent with emerging evidence that shows off-task thoughts emerge through the prioritisation of information that has greater personal relevance than events in the here and now

The psychological correlates of distinct neural states occurring during wakeful rest

When unoccupied by an explicit external task, humans engage in a wide range of different types of self-generated thinking. These are often unrelated to the immediate environment and have unique psychological features. Although contemporary perspectives on ongoing thought recognise the heterogeneity of these self-generated states, we lack both a clear understanding of how to classify the specific states, and how they can be mapped empirically. In the current study, we capitalise on advances in machine learning that allow continuous neural data to be divided into a set of distinct temporally re-occurring patterns, or states. We applied this technique to a large set of resting state data in which we also acquired retrospective descriptions of the participants' experiences during the scan. We found that two of the identified states were predictive of patterns of thinking at rest. One state highlighted a pattern of neural activity commonly seen during demanding tasks, and the time individuals spent in this state was associated with descriptions of experience focused on problem solving in the future. A second state was associated with patterns of activity that are commonly seen under less demanding conditions, and the time spent in it was linked to reports of intrusive thoughts about the past. Finally, we found that these two neural states tended to fall at either end of a neural hierarchy that is thought to reflect the brain's response to cognitive demands. Together, these results demonstrate that approaches which take advantage of time-varying changes in neural function can play an important role in understanding the repertoire of self-generated states. Moreover, they establish that important features of self-generated ongoing experience are related to variation along a similar vein to those seen when the brain responds to cognitive task demands

Neural basis of emotional awareness

Emotional awareness is the ability to recognize and describe emotion in oneself and others. A prominent theory postulates that emotional awareness depends on the cognitive skills developed for differentiation and integration of the schemata for processing emotional information. Nevertheless, emotional awareness might also depend on emotional experiences elicited at an earlier stage before emotional information are cognitively processed, especially the processing mechanisms involved in emotional attention and interoceptive awareness (sensing of bodily state). In order to explore the neural bases of emotional awareness, this thesis studied people with relatively extreme characteristics of emotional awareness, namely alexithymia and mindfulness. Study One explored the neural correlates of alexithymia, a condition reflecting a reduced level of emotional awareness in oneself, in 22 female depressive patients and 21 matched nonclinical controls. Degree of alexithymia was found to be associated with reducing white-matter diffusivity at corpus callosum for the patients and at right superior longitudinal fasciculus for the controls, confirming our a priori hypothesis that alexithymia in these two groups may be associated with different neural mechanisms. Further analysis using resting-state functional connectivity showed that increasing alexithymia in depressive patients was associated with decreasing coupling of right precentral gyrus and several right brain regions associated with self-reference and emotion regulation, while increasing alexithymia in controls was associated with increasing coupling between the prefrontal site for evaluating stimuli significance and the occipital site for gathering of perceptual information. These functional connectivity changes at different remote brain regions were interpreted as associated with the microstructural changes of the different neural correlates of alexithymia for the two groups. Study Two sought to substantiate the findings in Study One that alexithymia without depression would be associated with reduced detection of stimuli significance, by studying a non-depressive subject with lesions at the extrastriate cortex. The findings were interpreted as supportive of the proposal by attributing that the lesion might have impaired the colliculus-pulvinar-amygdala pathway for rapid evaluation of stimulus emotional significance. Study Three investigated 22 male meditation practitioners on their mindfulness, a trait associated with heightened level of emotional awareness, and neurophysiological reactivity upon perception of emotional stimuli. The results showed that mindfulness would predict both the behavioral ratings of stimulus valence and amplitudes of P2 (an ERP component) for the contrast between positive and negative stimuli. Combining these findings with the existing theories on mindfulness, a mechanism for explaining how mindfulness trait might contribute to reduce negativity bias was proposed. In summary, findings of the three studies described in this thesis would offer significant insights on how dynamic interactions of neural networks across both early and late stages of affective processing may have impacts on emotional awareness. In terms of clinical implications, firstly, our findings suggested that microstructural changes in corpus callosum might be specific to comorbid Type II alexithymia (high in cognitive characteristics only) in depressive patients. Secondly, mindfulness training might have implications on treatment of affective disorders that are associated with attentional bias, through its effect on negativity bias reduction.published_or_final_versionPsychologyDoctoralDoctor of Philosoph