1,720,986 research outputs found
Preliminary Findings Demonstrating Latent Effects of Early Adolescent Marijuana Use Onset on Cortical Architecture
No full textBackground: As the most commonly used illicit substance during early adolescence, long-term or latent effects of early adolescent marijuana use across adolescent developmental processes remain to be determined. Methods: We examined cortical thickness, gray/white matter border contrast (GWR) and local gyrification index (LGI) in 42 marijuana (MJ) users. Voxelwise regressions assessed early-onset (age = 16 years-old) differences and relationships to continued use while controlling for current age and alcohol use. Results: Although groups did not differ by onset status, groups diverged in their correlations between cannabis use and cortical architecture. Among early-onset users, continued years of MJ use and current MJ consumption were associated with thicker cortex, increased GWR and decreased LGI. Late-onset users exhibited the opposite pattern. This divergence was observed in all three morphological measures in the anterior dorsolateral frontal cortex (p < .05, FWE-corrected). Conclusions: Divergent patterns between current MJ use and elements of cortical architecture were associated with early MJ use onset. Considering brain development in early adolescence, findings are consistent with disruptions in pruning. However, divergence with continued use for many years thereafter suggests altered trajectories of brain maturation during late adolescence and beyond.This research was funded by the National Institute on Drug Abuse (R01 DA030344, Filbey)
Long-term effects of marijuana use on the brain.
No full textThe existing literature on the long-term effects of marijuana on the brain provides an inconsistent picture (i.e., presence or absence of structural changes) due to methodological differences across studies. We overcame these methodological issues by collecting multimodal measures in a large group of chronic marijuana using adults with a wide age range that allows for characterization of changes across lifespan without developmental or maturational biases as in other studies. Our findings suggest that chronic marijuana use is associated with complex neuroadaptive processes and that onset and duration of use have unique effects on these processes
Effects of Repetitive Transcranial Magnetic Stimulation on the Connectivity of the Resting-State Triple Network in Cannabis Users
No full textA large number of studies have reported the association between pathological neural diseases (e.g.,
addicted disorders) and abnormal interactions in a large-scale brain network which is called the
triple network. Cannabis users have shown dysfunctional interactions in the triple network during
resting state (RS), which has been related to problematic symptoms of cannabis use. Among
diverse tools, non-invasive repetitive transcranial magnetic stimulation (rTMS) has been
introduced as an effective tool to moderate aberrant activity in the triple network. The posterior
cingulate cortex (PCC) and precuneus are important hubs in the default mode network (DMN) and
have cannabinoid receptors targeted by delta 9 tetrahydrocannabinol (THC) which is the main
component of cannabis. This led us to test whether neuromodulation of these regions may
moderate dysfunctional interactions between the areas of the triple network at rest. To that end,
we collected electroencephalographic (EEG) recordings during RS after 10 Hz (high frequency,
HF) and 1 Hz rTMS (low frequency, LF) in 12 cannabis users and 11 non-cannabis users. Using
the exact Low-Resolution Electromagnetic Tomography (eLORETA) software, we examined
connectivity strength in the triple network with resting-state EEG recordings. The results showed
that HF rTMS to the PCC and precuneus has increased the delta connectivity following the LF
rTMS between DMN and central executive network (CEN) in cannabis users, specifically between
the PCC and left dorsolateral prefrontal cortex (dlPFC). In contrast, no effects of HF rTMS were
observed in non-cannabis users. To sum up, our results present that HF rTMS to the PCC and
precuneus can effectively modulate a partial connectivity (DMN-CEN) of large-scale network in
cannabis users
Adolescents show differential dysfunctions related to Alcohol and Cannabis Use Disorder severity in emotion and executive attention neuro-circuitries
No full textAlcohol and cannabis are two substances that are commonly abused by adolescents in the United States and which, when abused, are associated with negative medical and psychiatric outcomes across the lifespan. These negative psychiatric outcomes may reflect the detrimental impact of substance abuse on neural systems mediating emotion processing and executive attention. However, work indicative of this has mostly been conducted either in animal models or adults with Alcohol and/or Cannabis Use Disorder (AUD/CUD). Little work has been conducted in adolescent patients. In this study, we used the Affective Stroop task to examine the relationship in 82 adolescents between AUD and/or CUD symptom severity and the functional integrity of neural systems mediating emotional processing and executive attention. We found that AUD symptom severity was positively related to amygdala responsiveness to emotional stimuli and negatively related to responsiveness within regions implicated in executive attention and response control (i.e., dorsolateral prefrontal cortex, anterior cingulate cortex, precuneus) as a function of task performance. In contrast, CUD symptom severity was unrelated to amygdala responsiveness but positively related to responsiveness within regions including precuneus, posterior cingulate cortex, and inferior parietal lobule as a function of task performance. These data suggest differential impacts of alcohol and cannabis abuse on the adolescent brain. Keywords: Adolescent, Alcohol Use Disorder, Amygdala, Cannabis Use Disorder, fMRI, Prefrontal corte
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
Automatic and reproducible positioning of phase-contrast MRI for the quantification of global cerebral blood flow.
No full textPhase-Contrast MRI (PC-MRI) is a noninvasive technique to measure blood flow. In particular, global but highly quantitative cerebral blood flow (CBF) measurement using PC-MRI complements several other CBF mapping methods such as arterial spin labeling and dynamic susceptibility contrast MRI by providing a calibration factor. The ability to estimate blood supply in physiological units also lays a foundation for assessment of brain metabolic rate. However, a major obstacle before wider applications of this method is that the slice positioning of the scan, ideally placed perpendicular to the feeding arteries, requires considerable expertise and can present a burden to the operator. In the present work, we proposed that the majority of PC-MRI scans can be positioned using an automatic algorithm, leaving only a small fraction of arteries requiring manual positioning. We implemented and evaluated an algorithm for this purpose based on feature extraction of a survey angiogram, which is of minimal operator dependence. In a comparative test-retest study with 7 subjects, the blood flow measurement using this algorithm showed an inter-session coefficient of variation (CoV) of 4.07 ± 3.03%. The Bland-Altman method showed that the automatic method differs from the manual method by between -8% and 11%, for 95% of the CBF measurements. This is comparable to the variance in CBF measurement using manually-positioned PC MRI alone. In a further application of this algorithm to 157 consecutive subjects from typical clinical cohorts, the algorithm provided successful positioning in 89.7% of the arteries. In 79.6% of the subjects, all four arteries could be planned using the algorithm. Chi-square tests of independence showed that the success rate was not dependent on the age or gender, but the patients showed a trend of lower success rate (p = 0.14) compared to healthy controls. In conclusion, this automatic positioning algorithm could improve the application of PC-MRI in CBF quantification
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
Neural Mechanisms of Affective Processing in Obesity and Associations with Weight Loss
No full textObesity affects over one-third of the American population and is associated with a myriad of physiological and psychological health concerns. While obesity has a number of contributing factors, the most prevalent is consumption of food beyond caloric need. Thus, valuation of salient external stimuli is implicated, as well as approach- and avoidance behavior. These occur through affective processing, which drives an individual’s valuation and orientation toward valenced stimuli.
Affective processing abnormalities in individuals with obesity have been shown in the context of food, as well as other stimuli, including facial expression of emotion. However, to date, a direct comparison between facial affective processing in individuals with obesity and lean controls, as well as in individuals with obesity before and after weight loss, has not been examined. To that end, we used a facial affective processing task in a functional magnetic resonance imaging experiment to identify differences in affective processing between lean participants and participants with obesity, as well as participants with obesity before and after significant weight loss.
We found that lean individuals demonstrated greater bilateral insula activation when viewing neutral faces compared to affective faces, while participants with obesity demonstrated greater dorsolateral prefrontal cortex activity when viewing neutral faces compared to affective faces. Additionally, participants with obesity demonstrated increased functional connectivity within the affective network while viewing affective faces. However, there was no difference in affective processing in participants with obesity after weight loss. These results indicate that lean controls may demonstrate increased uncertainty and attention to neutral faces in an attempt to decipher unexpressed emotion, while participants with obesity may demonstrate greater executive control, perhaps in the maintenance of attention to faces without emotion expression.
In conclusion, these results suggest differences in affective processing between participants with obesity and lean controls, and a lack of change in affective processing after weight loss. These results may help guide future treatment options for obesity, particularly incorporating affective processing
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