70 research outputs found
Superhero scientists: shining the spotlight on diversity in scientific professions
No full textAuthors David Allen and Alex Sinclair discuss challenging stereotypes and interview MRI scientist Hamied Haroon
The Effects of Social Stress on Memory:If, How and When
No full textAbstract: Physical stress, such as from the cold-pressor test, has been robustly associated with altered memory retrieval, but it is not yet clear whether the same happens following psychosocial stress. Studies using psychosocial stressors report mixed effects on memory, leading to uncertainty about the common cognitive impact of both forms of stress. The current study uses a stepped replication design, with four near-identical experiments, each differing by a single critical factor. In three experiments we induced psychosocial stress after participants encoded word stimuli, then assessed retrieval after a prolonged delay. These experiments found no group level influence of postencoding stress on recognition of neutral words or cued recall of word-pairs, but a small effect on recollection of semantically-related words. There was, however, some indication of positive relationships within the stress group between measures of stress (cortisol in experiment 1 and self-reported-anxiety in experiment 3) and recollection of single word stimuli. In the fourth experiment, we found that psychosocial stress immediately before retrieval did not influence word recognition. Overall, our findings demonstrate that psychosocial stress has a typically modest impact on memory, lower than previously claimed, but that individual differences in stress responsivity, particularly for tasks that tap recollection, may help to explain variability in previous findings
Tractography dissection variability: what happens when 42 groups dissect 14 white matter bundles on the same dataset?
No full textAbstract: White matter bundle segmentation using diffusion MRI fiber tractography has become the method of choice to identify white matter fiber pathways in vivo in human brains. However, like other analyses of complex data, there is considerable variability in segmentation protocols and techniques. This can result in different reconstructions of the same intended white matter pathways, which directly affects tractography results, quantification, and interpretation. In this study, we aim to evaluate and quantify the variability that arises from different protocols for bundle segmentation. Through an open call to users of fiber tractography, including anatomists, clinicians, and algorithm developers, 42 independent teams were given processed sets of human wholebrain streamlines and asked to segment 14 white matter fascicles on six subjects. In total, we received 57 different bundle segmentation protocols, which enabled detailed volume-based and streamline-based analyses of agreement and disagreement among protocols for each fiber pathway. Results show that even when given the exact same sets of underlying streamlines, the variability across protocols for bundle segmentation is greater than all other sources of variability in the virtual dissection process, including variability within protocols and variability across subjects. In order to foster the use of tractography bundle dissection in routine clinical settings, and as a fundamental analytical tool, future endeavors must aim to resolve and reduce this heterogeneity. Although external validation is needed to verify the anatomical accuracy of bundle dissections, reducing heterogeneity is a step towards reproducible research and may be achieved through the use of standard nomenclature and definitions of white matter bundles and well-chosen constraints and decisions in the dissection process
Psychosocial stress has weaker than expected effects on episodic memory and related cognitive abilities: a meta-analysis
No full textThe impact of stress on episodic memory and related cognitive abilities is well documented in both animal and human literature. However, it is unclear whether the same cognitive effects result from all forms of stress - in particular psychosocial stress. This review systematically explored the effects of psychosocial stress on episodic memory and associated cognitive abilities. PubMed, PsycInfo, and Web of Science databases were searched. Fifty-one studies were identified and compared based on the timing of stress induction. A small positive effect of post-learning psychosocial stress with a long retention interval was shown. No other effects of psychosocial stress were seen. Re-analysis of previous meta-analyses also showed no significant effect of psychosocial stress on episodic memory, highlighting potentially different effects between stressor types. Psychosocial stress also had a moderately different effect when emotional vs. neutral stimuli were compared. Finally, psychosocial stress also decreased performance on executive function, but not working memory tasks. Our findings demonstrate that psychosocial stress may not have the clear effects on episodic memory previously ascribed to it
Distortion correction for diffusion-weighted MRI tractography and fMRI in the temporal lobes
No full textSingle shot echo-planar imaging (EPI) sequences are currently the most commonly used sequences for diffusion-weighted imaging (DWI) and functional magnetic resonance imaging (fMRI) as they allow relatively high signal to noise with rapid acquisition time. A major drawback of EPI is the substantial geometric distortion and signal loss that can occur due to magnetic field inhomogeneities close to air-tissue boundaries. If DWI-based tractography and fMRI are to be applied to these regions, then the distortions must be accurately corrected to achieve meaningful results. We describe robust acquisition and processing methods for correcting such distortions in spin echo (SE) EPI using a variant of the reversed direction k space traversal method with a number of novel additions. We demonstrate that dual direction k space traversal with maintained diffusion-encoding gradient strength and direction results in correction of the great majority of eddy current-associated distortions in DWI, in addition to those created by variations in magnetic susceptibility. We also provide examples to demonstrate that the presence of severe distortions cannot be ignored if meaningful tractography results are desired. The distortion correction routine was applied to SE-EPI fMRI acquisitions and allowed detection of activation in the temporal lobe that had been previously found using PET but not conventional fMRI. © 2010 Wiley-Liss, Inc
The effects of psychosocial stress on item, cued‐pair and emotional memory
No full textAbstract: Physical stress, such as from the cold‐pressor test, has been robustly associated with altered memory retrieval, but it is less clear whether the same happens following psychosocial stress. Studies using psychosocial stressors report mixed effects on memory, leading to uncertainty about the common cognitive impact of both forms of stress. The current study uses a series of four carefully designed experiments, each differing by only a single critical factor to determine the effects of psychosocial stress on specific aspects of episodic memory. In three experiments, we induced psychosocial stress after participants encoded words, then assessed retrieval of those words after a prolonged delay. These experiments found no effect of post‐encoding stress on recognition of neutral words or cued recall of word‐pairs, but a small effect on recollection of semantically related words. There were, however, positive relationships within the stress group between measures of stress (cortisol in experiment 1 and self‐reported‐anxiety in experiment 3) and recollection of single word stimuli. In the fourth experiment, we found that psychosocial stress immediately before retrieval did not influence word recognition. Recollection, particularly for semantically related stimuli, may therefore be more susceptible to the effects of psychosocial stress, and future studies can assess how this relates to other forms of stress. Overall, our findings suggest that the effects of psychosocial stress on episodic memory may be more subtle than expected, warranting further exploration in larger studies
The Effects of Psychosocial Stress on Memory and Cognitive Ability: A Meta-Analysis
No full textThe impact of stress on cognitive abilities, such as memory, is well documented in animal studies but it is not yet clear how stress in human social interactions affects memory. This review systematically explored the evidence regarding the effects of psychosocial stress on memory and associated cognitive abilities. PubMed, PsycInfo and Web of Science databases were searched for studies assessing the effects of psychosocial stress on long-term memory or related cognitive functions. Fifty-one studies were identified and compared based on the timing of stress induction. No overall effect of psychosocial stress induction was seen on long-term or working memory regardless of whether stress induction occurred following encoding or before retrieval. Psychosocial stress had a moderate effect in studies comparing memory for emotional compared to neutral stimuli, but the direction of this effect varied across studies. Psychosocial stress decreased performance on executive function tasks. Our findings demonstrate that psychosocial stress may not have the clear effects on memory previously ascribed to it, suggesting potentially different mechanisms from physiological stressors
Experimental Validation of a Prototype for Fault Detection and Classification of a Photovoltaic System Using dSPACE
No full textInternational audienceIn this paper, an experimental validation of a low-cost prototype for fault detection and classification of a photovoltaic (PV) system is presented. The prototype can detect, classify faults and displaying the results on the website via Internet of Things (IoT). The experiments result have been carried out at MIS Laboratory of Picardie Jules Verne University, (France). The code is developed under Matlab/Simulink environment and then implemented into a dSPACE- 1104 for experimental verification. The obtained results of the developed prototype offer similar results as the one obtained using a dSPACE-1104. This confirm the accuracy of the implemented fault detection and classification algorithm (the investigated fault are: short-circuit, open-circuit, shading effect, and dust accumulations on PV modules). \textcopyright 2020, The Author(s), under exclusive license to Springer Nature Switzerland AG
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