1,720,973 research outputs found
Replication Data for: "Regional response to light illuminance across the human hypothalamus"
No full textContrast image used to extract beta estimates
Multimodal Investigation of Non-Image Forming Effects of Light on the Brain: Impact of Time of Day and Developmental Stage
No full textLighting can significantly influence various aspects of our life, including health, performance, and behavior. Inappropriate lighting is associated with numerous challenges in these areas, while appropriate lighting can enhance well-being and functionality. Key factors such as timing, intensity, and spectral composition play crucial roles in determining appropriate versus inappropriate lighting conditions. The human brain processes light via two pathways: the classical visual system, responsible for image formation, and the non-image forming (NIF) system, which reacts to environmental light levels. The NIF system is especially sensitive to shorter blue wavelengths (~480 nm), influencing circadian rhythms, neuroendocrine functions, and neurobehavioral responses.
Over the years, lighting technology has transitioned from incandescent and fluorescent bulbs to energy-efficient light emitting diodes (LEDs). This shift has altered the spectral composition of indoor lighting, increasing the prevalence of blue light, as typical "white" LEDs peak between 440- 460 nm. Moreover, the widespread use of LEDs has extended our exposure to blue-enriched light into biological night, which can be detrimental to health by disrupting circadian rhythms and other physiological processes. Given these developments, it is essential to understand how light interacts with the brain and influences its functions beyond vision. Furthermore, the understanding of the NIF system, combined with advancements in LED technology, has given rise to the concept of integrative lighting, which aims to optimize both visual clarity and biological effects. To maximize the health benefits of integrative lighting and minimize adverse impacts, it is essential to investigate how light affects brain function and how factors like age and timing of exposure modulate these effects.
To further explore the NIF effects of light on human brain, we employed ultra-high-field 7 Tesla (UHF 7T) functional magnetic resonance imaging (fMRI) for its high resolution, allowing us to image small subcortical structures affected by light, such as the hypothalamus and thalamus nuclei. Healthy adolescents and young adults participated in an fMRI protocol at various times of day while exposed to different light intensities and engaged in auditory cognitive tasks. Additionally, we used transcranial magnetic stimulation combined with electroencephalography (TMS-EEG) to assess NIF effects at the cortical level, with participants completing a TMS-EEG protocol in the afternoon under varying light conditions.
In this thesis, we initially focused on understanding how light affects one of its primary targets: the hypothalamus. This involved two studies. We first investigated whether there were regional variations in response to light exposure within the human hypothalamus during cognitive tasks in the morning among young adults. The results indicated distinct response patterns to increasing light levels across different regions of the hypothalamus. Notably, higher light levels led to increased activity in the posterior hypothalamus, while the anterior and ventral regions showed reduced activity. This suggests that the posterior hypothalamus may be a key area where light stimulates cognition and alertness, potentially through mechanisms involving orexin and histamine signaling.
We expanded this investigation by doing fMRI in the evening and including adolescents to assess how time-of-day and developmental age influence hypothalamic response dynamics. The findings reinforced the anterior-posterior gradient observed in response to varying light levels. Specifically, increased illuminance continued to activate the posterior hypothalamus while decreasing activity in the anterior and ventral regions during the evening and in adolescents. Time-of-day did not alter the hypothalamic response, while age did; adolescents exhibited a stronger response to light compared to adults, showing more significant deactivation in the anterior and ventral regions. This suggests greater sensitivity in adolescents and highlights other functional differences related to age.
Next, we investigated the thalamus' established role in NIF functions, as highlighted in the literature. Given its key position as a central hub in the brain' signaling network, the thalamus likely plays a crucial role in relaying NIF signals to the cortex, thereby influencing alertness and cognitive function. In this context, we hypothesized that the impact of light on cognition might extends beyond altering regional activity to also affect functional connectivity throughout the brain.
Our third study focused therefore on how light affects functional connectivity between the thalamus and two cortical regions involved in executive functions, particularly working memory. We examined how light modulates connectivity among these areas while considering age and time-of-day differences. Our findings revealed that moderate illuminance blue-enriched light enhanced a cortico-cortical connectivity across all groups. Interestingly, low illuminance orange light also strengthened a connectivity from the thalamus to one of the cortical regions. Additionally, both time-of-day and age influenced how light affected connectivity. For instance, the highest illuminance blue-enriched light strengthened the thalamus-to-medial frontal gyrus connectivity in the morning among adults. Moreover, moderate illuminance blue-enriched light positively impacted the thalamus-to-supramarginal gyrus connectivity in adolescents. This investigation deepens our understanding of the complex neural mechanisms by which light affects cognitive processes and highlights the role of time-of-day and age.
In the final study, we extended our investigation to cortical level by using TMS-EEG to examine, for the first time, the effect of light on cortical excitability. Our findings revealed a distinct response between adolescents and adults. While cortical excitability in adults followed an apparent inverted U-shaped function with increasing illuminance, light showed no effect on cortical excitability in adolescents. These results further emphasize the different sensitivity of adolescents to light.
Overall, this thesis explores aspects of the brain circuitry involved in how light affects cognitive functions. It emphasizes the significance of factors like time-of-day and age, highlighting that a deeper understanding of how light influences cognitive processes and its modulatory factors can lead to integrative lighting solutions that promote health and well-being in the future.TEENLIGH
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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