The meditative mind: a comprehensive meta-analysis of MRI studies

Over the past decade mind and body practices, such as yoga and meditation, have raised interest in different scientific fields; in particular, the physiological mechanisms underlying the beneficial effects observed in meditators have been investigated. Neuroimaging studies have studied the effects of meditation on brain structure and function and findings have helped clarify the biological underpinnings of the positive effects of meditation practice and the possible integration of this technique in standard therapy. The large amount of data collected thus far allows drawing some conclusions about the neural effects of meditation practice. In the present study we used activation likelihood estimation (ALE) analysis to make a coordinate-based meta-analysis of neuroimaging data on the effects of meditation on brain structure and function. Results indicate that meditation leads to activation in brain areas involved in processing self-relevant information, self-regulation, focused problem-solving, adaptive behavior, and interoception. Results also show that meditation practice induces functional and structural brain modifications in expert meditators, especially in areas involved in self-referential processes such as self-awareness and self-regulation. These results demonstrate that a biological substrate underlies the positive pervasive effect of meditation practice and suggest that meditation techniques could be adopted in clinical populations and to prevent disease

Effects of healthy ageing on the precision of episodic memory

Episodic memory decline is one of the hallmarks of human cognitive ageing, but our understanding of the neurocognitive mechanisms underlying this decline remains limited. In particular, it is unclear whether healthy ageing differentially affects distinct components of episodic memory retrieval; specifically, the probability of successfully retrieving information from memory, and the quality, or precision, of the retrieved memory representations. The research reported in this PhD thesis used continuous measures of memory retrieval to dissociate these two alternative sources of age-related memory deficits and their cognitive and neural underpinnings, providing more detailed insight into the nature of age-related episodic memory decline. Two behavioural experiments reported in Chapter 2 provided initial evidence for differential effects of healthy ageing on the success and precision of episodic memory retrieval, suggesting greater sensitivity of mnemonic precision to age-related declines. Chapter 3 assessed whether these decreases in memory precision are specific to long-term memory or may be explained by age-related decreases in the fidelity of perceptual or working memory processes. The results from this experiment demonstrated that age-related reductions in the precision of episodic memory retrieval persisted after controlling for decreases in the fidelity of perception and working memory, suggesting a predominantly long-term memory basis for this deficit. The functional and structural magnetic resonance imaging experiments reported in Chapters 4 and 5 sought to elucidate the neural basis of age-related changes in the success and precision of episodic memory retrieval. Results from Chapter 4 revealed distinct encoding and retrieval contributions to the decreases in these two aspects of memory retrieval exhibited by older adults. At retrieval, age-related reductions in activity associated with successful memory retrieval were observed in the hippocampus, while decreases in activity underlying the precision of memory retrieval were evident in the angular gyrus. Furthermore, at encoding, age-related decreases in activity predicting both later success and precision of memory retrieval were evident in the fusiform gyrus, while prefrontal reductions were observed in the encoding activity predicting the subsequent success of memory retrieval only. In addition to these functional changes, Chapter 5 provided evidence for the role of structural integrity of the lateral parietal cortex in individual differences in mnemonic precision across older adults. Together, the results reported in this thesis highlight the sensitivity of memory precision to age-related cognitive decline, and suggest both distinct and common factors underlying age-related decreases in the success and precision of episodic memory retrieval

Fluid reasoning and the developing brain.

Fluid reasoning is the cornerstone of human cognition, both during development and in adulthood. Despite this, the neural mechanisms underlying the development of fluid reasoning are largely unknown. In this review, we provide an overview of this important cognitive ability, the method of measurement, its changes over the childhood and adolescence of an individual, and its underlying neurobiological underpinnings. We review important findings from psychometric, cognitive, and neuroscientific literatures, and outline important future directions for this interdisciplinary research

An Efficient Method for online Detection of Polychronous Patterns in Spiking Neural Network

Polychronous neural groups are effective structures for the recognition of precise spike-timing patterns but the detection method is an inefficient multi-stage brute force process that works off-line on pre-recorded simulation data. This work presents a new model of polychronous patterns that can capture precise sequences of spikes directly in the neural simulation. In this scheme, each neuron is assigned a randomized code that is used to tag the post-synaptic neurons whenever a spike is transmitted. This creates a polychronous code that preserves the order of pre-synaptic activity and can be registered in a hash table when the post-synaptic neuron spikes. A polychronous code is a sub-component of a polychronous group that will occur, along with others, when the group is active. We demonstrate the representational and pattern recognition ability of polychronous codes on a direction selective visual task involving moving bars that is typical of a computation performed by simple cells in the cortex. The computational efficiency of the proposed algorithm far exceeds existing polychronous group detection methods and is well suited for online detection.Comment: 17 pages, 8 figure

Brain regions that process case: Evidence from basque

The aim of this event-related fMRI study was to investigate the cortical networks involved in case processing, an operation that is crucial to language comprehension yet whose neural underpinnings are not well-understood. What is the relationship of these networks to those that serve other aspects of syntactic and semantic processing? Participants read Basque sentences that contained case violations, number agreement violations or semantic anomalies, or that were both syntactically and semantically correct. Case violations elicited activity increases, compared to correct control sentences, in a set of parietal regions including the posterior cingulate, the precuneus, and the left and right inferior parietal lobules. Number agreement violations also elicited activity increases in left and right inferior parietal regions, and additional activations in the left and right middle frontal gyrus. Regions-of-interest analyses showed that almost all of the clusters that were responsive to case or number agreement violations did not differentiate between these two. In contrast, the left and right anterior inferior frontal gyrus and the dorsomedial prefrontal cortex were only sensitive to semantic violations. Our results suggest that whereas syntactic and semantic anomalies clearly recruit distinct neural circuits, case, and number violations recruit largely overlapping neural circuits and that the distinction between the two rests on the relative contributions of parietal and prefrontal regions, respectively. Furthermore, our results are consistent with recently reported contributions of bilateral parietal and dorsolateral brain regions to syntactic processing, pointing towards potential extensions of current neurocognitive theories of language. Hum Brain Mapp, 2012. © 2011 Wiley Periodicals, Inc

Prospective Memory in Older Adults : Where We Are Now and What Is Next

M. Kliegel acknowledges financial support from the Swiss National Science Foundation (SNSF).Peer reviewedPostprin

Multiscale and multimodal network dynamics underpinning working memory

Working memory (WM) allows information to be stored and manipulated over short time scales. Performance on WM tasks is thought to be supported by the frontoparietal system (FPS), the default mode system (DMS), and interactions between them. Yet little is known about how these systems and their interactions relate to individual differences in WM performance. We address this gap in knowledge using functional MRI data acquired during the performance of a 2-back WM task, as well as diffusion tensor imaging data collected in the same individuals. We show that the strength of functional interactions between the FPS and DMS during task engagement is inversely correlated with WM performance, and that this strength is modulated by the activation of FPS regions but not DMS regions. Next, we use a clustering algorithm to identify two distinct subnetworks of the FPS, and find that these subnetworks display distinguishable patterns of gene expression. Activity in one subnetwork is positively associated with the strength of FPS-DMS functional interactions, while activity in the second subnetwork is negatively associated. Further, the pattern of structural linkages of these subnetworks explains their differential capacity to influence the strength of FPS-DMS functional interactions. To determine whether these observations could provide a mechanistic account of large-scale neural underpinnings of WM, we build a computational model of the system composed of coupled oscillators. Modulating the amplitude of the subnetworks in the model causes the expected change in the strength of FPS-DMS functional interactions, thereby offering support for a mechanism in which subnetwork activity tunes functional interactions. Broadly, our study presents a holistic account of how regional activity, functional interactions, and structural linkages together support individual differences in WM in humans