1,720,969 research outputs found
The visual system as target of non-invasive brain stimulation for migraine treatment: Current insights and future challenges
No full textThe visual network is crucially implicated in the pathophysiology of migraine. Several lines of evidence indicate that migraine is characterized by an altered visual cortex excitability both during and between attacks. Visual symptoms, the most common clinical manifestation of migraine aura, are likely the result of cortical spreading depression originating from the extrastriate area V3A. Photophobia, a clinical hallmark of migraine, is linked to an abnormal sensory processing of the thalamus which is converged with the non-image forming visual pathway. Finally, visual snow is an increasingly recognized persistent visual phenomenon in migraine, possibly caused by increased perception of subthreshold visual stimuli.
Emerging research in non-invasive brain stimulation (NIBS) has vastly developed into a diversity of areas with promising potential. One of its clinical applications is the single-pulse transcranial magnetic stimulation (sTMS) applied over the occipital cortex which has been approved for treating migraine with aura, albeit limited evidence. Studies have also investigated other NIBS techniques, such as repetitive TMS (rTMS) and transcranial direct current stimulation (tDCS), for migraine prophylaxis but with conflicting results. As a dynamic brain disorder with widespread pathophysiology, targeting migraine with NIBS is challenging. Furthermore, unlike the motor cortex, evidence suggests that the visual cortex may be less plastic. Controversy exists as to whether the same fundamental principles of NIBS, based mainly on findings in the motor cortex, can be applied to the visual cortex.
This review aims to explore existing literature surrounding NIBS studies on the visual system of migraine. We will first provide an overview highlighting the direct implication of the visual network in migraine. Next, we will focus on the rationale behind using NIBS for migraine treatment, including its effects on the visual cortex, and the shortcomings of currently available evidence. Finally, we propose a broader perspective of how novel approaches, the concept of brain networks and the integration of multimodal imaging with computational modeling, can help refine current NIBS methods, with the ultimate goal of optimizing a more individualized treatment for migraine
Clinical and biobehavioral perspectives: Is medication overuse headache a behavior of dependence?
No full textMedication overuse headache (MOH), previously known as analgesic abuse headache or medication misuse headaches, is a common form of chronic headache disorder that has a detrimental impact on health and society. Although it has been widely accepted that overusing abortive medications is paradoxically the cause of MOH and drug discontinuation is the treatment of choice, ongoing debates exist as to whether drug consumption per se is the cause or consequence of headache chronification. Certain features in MOH such as their compulsive drug-seeking behavior, withdrawal headaches and high relapse rates share similarities with drug dependence, suggesting that there might be common underlying biological and psychobehavioral mechanisms. In this regard, this article will discuss the updated evidence and current debates on the possible biobehavioral overlap between MOH and drug dependence.
To begin with, we will discuss whether MOH has characteristics of substance dependence based on standard psychiatry diagnostic criteria and other widely used dependence scales. Recent epidemiological studies underscoring common psychiatric comorbidities between the two disorders will also be presented. Although both demonstrate seemingly distinct personality traits, recent studies revealed similar decision-making impairment from a cognitive perspective, indicating the presence of a maladaptive reward system in both disorders. In addition, emerging imaging studies also support this notion by showing reversible morphological and functional brain changes related to the mesocorticolimbic reward circuitry in MOH, with a strong resemblance to those in addiction. Finally, an increased familial risk for drug dependence and genetic association with dopaminergic and drug dependence molecular pathways in MOH also support a possible link between MOH and addiction. Understanding the role of dependence in MOH will have a great impact on disease management as this will provide the missing piece of the puzzle in current therapeutic strategies
Exploring the mechanisms of chronic migraine: insights from behaviour, physiology and advanced neuroimaging
No full textChronic migraine (CM) often co-occurs with a debilitating condition known as medication overuse headache (MOH), where headaches paradoxically worsen due to medication overuse. The reasons some CM patients are prone to MOH remain unclear, but psychological factors such as pain perception or medication decision- making may play a role. This thesis explores these aspects through behavioural, neuroimaging, and physiological experiments.
The first study compared decision-making in CM patients with MOH, CM patients without MOH, and healthy controls. CM patients with MOH showed impaired decision-making under ambiguity but not under risk. Their performance inversely correlated with analgesic consumption, suggesting a link between decision-making under ambiguity and MOH.
The second study investigated the neural mechanisms underlying these findings. CM patients with MOH had reduced cortical thickness and subcortical nuclei volume in key components of the mesocorticolimbic reward circuity compared to those without MOH. Anterior cingulate cortical thickness inversely correlated with substance dependence scale, supporting the hypothesis that medication overuse in CM patients is related to a dysregulated reward system.
Subsequently, I explored the potential to modulate cortical excitability in the visual cortex using transcranial direct current stimulation (tDCS). My third study showed a deficient habituation of pattern-reversal visual evoked potential (VEP) response in migraine patients compared to healthy controls. However, the final study found no significant tDCS effects on VEP amplitudes or habituation slopes in heathy subjects, questioning assumptions about polarity-specific tDCS effects in the visual cortex and suggesting that common tDCS protocols for the motor cortex may not be effective for the visual cortex.
Collectively, these findings provide novel evidence that CM with MOH is linked to a dysregulated reward system. The lack of durable tDCS effects in the visual cortex indicates a different susceptibility to tDCS compared to the motor cortex. Future studies with alternative methods are warranted to explore potential therapeutic effects of tDCS for migraine
Light, photophobia and headache: an investigation of visually-induced migraine
Full text linkExacerbation of headache by light is a major symptom in migraine. A recent study unraveled the non-image forming (NIF) visual pathway to be a key component underlying photophobia in migraine. Several lines of evidence also indicate that an altered cortical excitability may render migraineurs more susceptible to attacks, although it is unclear whether the cortex is more or less excitable. Accordingly, this thesis investigated the link between migraine, visual systems and brain responsiveness using three complementary approaches. To begin with, I assessed the response of the NIF visual system to light of different wavelengths in healthy subjects. My results provided the first neuroimaging evidence that the suprachiasmatic nucleus (SCN) of the NIF system displays a sustained response to blue light but not to other wavelengths. This highlights the unique property of the SCN for mediating the circadian cycle, which some investigators have suggested drive the periodicity of migraine attacks. Next, I examined the interictal cortical sensitivity to light and visual stimuli in migraine. The fMRI results revealed a hypo-excitable response to diffuse illumination in migraineurs compared to healthy controls. The response, however, did not differ when subjects were exposed to a more aversive flickering checkerboard stimulus. Furthermore, the phenomenon appeared to be magnified in a group harboring the TRESK variant, who may be considered an extreme form of the migraine spectrum. This suggests that the initial cortical hypo- excitability may serve as a protective mechanism against further attacks. Surprisingly, I found no disturbance of glutamate, GABA and NAA in the visual cortex of interictal migraine subjects, arguing against the notion that these metabolites may mediate the protective mechanism or predispose the brain to migraine attacks. Finally, I optimized the PCR and prepared a DNA pool of 741 migraineurs and 416 controls for sequencing four candidate genes including TRESK and OPN4. Variants identified in these genes that associate with migraine may provide mechanistic insights into how genetic backgrounds alters neuronal and brain responsiveness and how this in turn increases migraine liability. Taken together, my studies reveal cortical hypo-excitability in patients with migraine between attacks and established a foundation for future studies including the NIF visual system in migraine. Longitudinal studies will also help unravel compensatory from primary changes in the migraine brain
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
- …
