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Task-related functional connectivity ( fc-MRI ) indexes the interaction of brain regions during cognitive tasks. Two general classes of methods exist to investigate fc-MRI: the most widely-used method calculates temporal correlations between voxels/regions within subjects, and then determines if within-subject correlations are reliable across subjects ( ws-fcMRI ); the other calculates the average (BOLD) signal within voxels/regions and then performs correlations across subjects ( as-fcMRI ). That is, while both methods rely on correlational techniques, the level at which correlations are calculated is fundamentally different. While conceptually distinct, it is not known how well these two methods of fc-MRI analyses converge on the same findings. The current study addresses this question across a number of analyses. First, using default-mode network regions as seeds, we show that as-fcMRI does not strongly predict ws-fcMRI during episodic simulation tasks. Next, we show that the relationship between as-fcMRI and ws-fcMRI is contingent on whether correlations are calculated between regions from the same functional network (default mode or dorsal attention networks) or between regions from different functional networks. Lastly, we compare seed partial least squares (PLS) – a well-established as-fcMRI method – with a novel version of seed PLS that combines the multivariate approach of PLS analyses and within-subject correlations. The results showed that while many regions exhibited congruent as-fcMRI and ws-fcMRI effects, in some regions the two analyses produced effects in opposite directions. Results are discussed in relation to the Simpson's Paradox, a phenomenon in which across-subject correlations are reversed within individuals present in a sample. Overall, our results suggest that the findings of as-fcMRI do not always map onto those from ws-fcMRI . We end by discussing the advantages associated with using ws-fcMRI to assess the task-related interactions between brain regions. [ABSTRACT FROM AUTHOR]

In a range of externally-directed tasks, intra-individual variability of fMRI BOLD signal has been shown to be a stronger predictor of cognitive performance than mean BOLD signal. BOLD variability's strong association with cognitive performance is hypothesised to be due to it capturing the dynamic range of neural systems. Although increased BOLD variability is also speculated to play a role in internally-directed thought, particularly when creative and flexible cognition is required, there is a relative lack of research exploring whether BOLD variability is related to internally-directed cognition. Thus, we investigated the relationship between BOLD variability and a key component of creativity – divergent thinking – in various tasks that required participants to think flexibly. We also determined whether any associations between BOLD variability and creativity overlapped with, or differed, from associations between mean BOLD signal and creativity. First, we performed task Partial Least Squares (PLS) analyses that compared BOLD signal (either mean or variability) during two future imagination conditions that differed in the amount of cognitive flexibility required: a Congruent condition in which autobiographical details (people, places, objects) comprising an imagined event belonged to the same social sphere (e.g., university) and an Incongruent condition in which details belonged to different social spheres and required greater cognitive flexibility to integrate. Results indicated that the Incongruent condition was associated with a widespread reduction in both BOLD variability and mean signal (relative to the Congruent condition), but in largely non-overlapping regions. Next, we used behavioral PLS to determine whether individual differences in performance on future simulation tasks as well as the Alternate Uses Task relates to BOLD variability and mean BOLD signal. Better performance on these tasks was predominantly associated with increases in mean BOLD signal and decreases in BOLD variability, in a range of disparate brain regions. Together, the results suggest that, unlike tasks requiring externally-directed cognition, superior performance on tasks requiring creative internal mentation is associated with less (not more) variability. • Imagination task requiring creativity caused decreases in BOLD mean and variability. • Creative individuals showed increased BOLD mean during imagination tasks. • Creative individuals showed reduced BOLD variability during imagination tasks. • The spatial distribution of mean and variability effects were largely non-overlapping. [ABSTRACT FROM AUTHOR]

Dyslexia is a developmental disorder characterized by reading and phonological difficulties, yet important questions remain regarding its underlying neural correlates. In this study, we used partial least squares (PLS), a multivariate analytic technique, to investigate the neural networks used by dyslexics while performing a word-rhyming task. Although the overall reading network was largely similar in dyslexics and typical readers, it did not correlate with behavior in the same way in the two groups. In particular, there was a positive association between reading performance and both right superior temporal gyrus and bilateral insula activation in dyslexic readers but a negative correlation in typical readers. Together with differences in lateralization unique to dyslexics, this suggests that the combination of poor reading performance with high insula activity and atypical laterality is a consistent marker of dyslexia. These findings emphasize the importance of understanding right-hemisphere activation in dyslexia and provide promising directions for the remediation of reading disorders. [ABSTRACT FROM AUTHOR]

Abstract: Models of autobiographical memory propose two routes to retrieval depending on cue specificity. When available cues are specific and personally-relevant, a memory can be directly accessed. However, when available cues are generic, one must engage a generative retrieval process to produce more specific cues to successfully access a relevant memory. The current study sought to characterize the neural bases of these retrieval processes. During functional magnetic resonance imaging (fMRI), participants were shown personally-relevant cues to elicit direct retrieval, or generic cues (nouns) to elicit generative retrieval. We used spatiotemporal partial least squares to characterize the spatial and temporal characteristics of the networks associated with direct and generative retrieval. Both retrieval tasks engaged regions comprising the autobiographical retrieval network, including hippocampus, and medial prefrontal and parietal cortices. However, some key neural differences emerged. Generative retrieval differentially recruited lateral prefrontal and temporal regions early on during the retrieval process, likely supporting the strategic search operations and initial recovery of generic autobiographical information. However, many regions were activated more strongly during direct versus generative retrieval, even when we time-locked the analysis to the successful recovery of events in both conditions. This result suggests that there may be fundamental differences between memories that are accessed directly and those that are recovered via the iterative search and retrieval process that characterizes generative retrieval. [Copyright &y& Elsevier]