| 31. |
- Gleich, Tobias, et al.
(författare)
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Prefrontal and Striatal Glutamate Differently Relate to Striatal Dopamine : Potential Regulatory Mechanisms of Striatal Presynaptic Dopamine Function?
- 2015
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Ingår i: Journal of Neuroscience. - : Society for Neuroscience. - 0270-6474 .- 1529-2401. ; 35:26, s. 9615-9621
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Tidskriftsartikel (refereegranskat)abstract
- Theoretical and animal work has proposed that prefrontal cortex (PFC) glutamate inhibits dopaminergic inputs to the ventral striatum (VS) indirectly, whereas direct VS glutamatergic afferents have been suggested to enhance dopaminergic inputs to the VS. In the present study, we aimed to investigate relationships of glutamate and dopamine measures in prefrontostriatal circuitries of healthy humans. We hypothesized that PFC and VS glutamate, as well as their balance, are differently associated with VS dopamine. Glutamate concentrations in the left lateral PFC and left striatum were assessed using 3-Tesla proton magnetic resonance spectroscopy. Striatal presynaptic dopamine synthesis capacity was measured by fluorine-18-l-dihydroxyphenylalanine (F-18-FDOPA) positron emission tomography. First, a negative relationship was observed between glutamate concentrations in lateral PFC and VS dopamine synthesis capacity (n = 28). Second, a positive relationship was revealed between striatal glutamate and VS dopamine synthesis capacity (n = 26). Additionally, the intraindividual difference between PFC and striatal glutamate concentrations correlated negatively with VS dopamine synthesis capacity (n = 24). The present results indicate an involvement of a balance in PFC and striatal glutamate in the regulation of VS dopamine synthesis capacity. This notion points toward a potential mechanism how VS presynaptic dopamine levels are kept in a fine-tuned range. A disruption of this mechanism may account for alterations in striatal dopamine turnover as observed in mental diseases (e.g., in schizophrenia).SIGNIFICANCE STATEMENT The present work demonstrates complementary relationships between prefrontal and striatal glutamate and ventral striatal presynaptic dopamine using human imaging measures: a negative correlation between prefrontal glutamate and presynaptic dopamine and a positive relationship between striatal glutamate and presynaptic dopamine are revealed. The results may reflect a regulatory role of prefrontal and striatal glutamate for ventral striatal presynaptic dopamine levels. Such glutamate–dopamine relationships improve our understanding of neurochemical interactions in prefrontostriatal circuits and have implications for the neurobiology of mental disease.
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| 32. |
- Hurtig, Per, 1980-, et al.
(författare)
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Low-Latency Scheduling in MPTCP
- 2019
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Ingår i: IEEE/ACM Transactions on Networking. - : IEEE. - 1063-6692 .- 1558-2566. ; 1, s. 302-315
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Tidskriftsartikel (refereegranskat)abstract
- The demand for mobile communication is continuously increasing, and mobile devices are now the communication device of choice for many people. To guarantee connectivity and performance, mobile devices are typically equipped with multiple interfaces. To this end, exploiting multiple available interfaces is also a crucial aspect of the upcoming 5G standard for reducing costs, easing network management, and providing a good user experience. Multi-path protocols, such as multi-path TCP (MPTCP), can be used to provide performance optimization through load-balancing and resilience to coverage drops and link failures, however, they do not automatically guarantee better performance. For instance, low-latency communication has been proven hard to achieve when a device has network interfaces with asymmetric capacity and delay (e.g., LTE and WLAN). For multi-path communication, the data scheduler is vital to provide low latency, since it decides over which network interface to send individual data segments. In this paper, we focus on the MPTCP scheduler with the goal of providing a good user experience for latency-sensitive applications when interface quality is asymmetric. After an initial assessment of existing scheduling algorithms, we present two novel scheduling techniques: the block estimation (BLEST) scheduler and the shortest transmission time first (STTF) scheduler. BLEST and STTF are compared with existing schedulers in both emulated and real-world environments and are shown to reduce web object transmission times with up to 51% and provide 45% faster communication for interactive applications, compared with MPTCP's default scheduler.
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| 33. |
- Karch, Julian D, et al.
(författare)
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Identifying predictors of within-person variance in MRI-based brain volume estimates
- 2019
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Ingår i: NeuroImage. - : Elsevier BV. - 1095-9572 .- 1053-8119. ; 200, s. 575-589
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Tidskriftsartikel (refereegranskat)abstract
- Adequate reliability of measurement is a precondition for investigating individual differences and age-related changes in brain structure. One approach to improve reliability is to identify and control for variables that are predictive of within-person variance. To this end, we applied both classical statistical methods and machine-learning-inspired approaches to structural magnetic resonance imaging (sMRI) data of six participants aged 24-31 years gathered at 40-50 occasions distributed over 6-8 months from the Day2day study. We explored the within-person associations between 21 variables covering physiological, affective, social, and environmental factors and global measures of brain volume estimated by VBM8 and FreeSurfer. Time since the first scan was reliably associated with Freesurfer estimates of grey matter volume and total cortex volume, in line with a rate of annual brain volume shrinkage of about 1 percent. For the same two structural measures, time of day also emerged as a reliable predictor with an estimated diurnal volume decrease of, again, about 1 percent. Furthermore, we found weak predictive evidence for the number of steps taken on the previous day and testosterone levels. The results suggest a need to control for time-of-day effects in sMRI research. In particular, we recommend that researchers interested in assessing longitudinal change in the context of intervention studies or longitudinal panels make sure that, at each measurement occasion, (a) a given participant is measured at the same time of day; (b) participants overall are measured at about the same time of day. Furthermore, the potential effects of physical activity, including moderate amounts of aerobic exercise, and testosterone levels on MRI-based measures of brain structure deserve further investigation.
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| 34. |
- Kühn, Simone, et al.
(författare)
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Brain areas consistently linked to individual differences in perceptual decision-making in younger as well as older adults before and after training
- 2011
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Ingår i: Journal of cognitive neuroscience. - Cambridge, Mass. : MIT Press. - 0898-929X .- 1530-8898. ; 23:9, s. 2147-2158
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Tidskriftsartikel (refereegranskat)abstract
- Perceptual decision-making performance depends on several cognitive and neural processes. Here, we fit Ratcliff's diffusion model to accuracy data and reaction-time distributions from one numerical and one verbal two-choice perceptual-decision task to deconstruct these performance measures into the rate of evidence accumulation (i.e., drift rate), response criterion setting (i.e., boundary separation), and peripheral aspects of performance (i.e., nondecision time). These theoretical processes are then related to individual differences in brain activation by means of multiple regression. The sample consisted of 24 younger and 15 older adults performing the task in fMRI before and after 100 daily 1-hr behavioral training sessions in a multitude of cognitive tasks. Results showed that individual differences in boundary separation were related to striatal activity, whereas differences in drift rate were related to activity in the inferior parietal lobe. These associations were not significantly modified by adult age or perceptual expertise. We conclude that the striatum is involved in regulating response thresholds, whereas the inferior parietal lobe might represent decision-making evidence related to letters and numbers.
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| 35. |
- Kühn, Simone, et al.
(författare)
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Spend time outdoors for your brain–an in-depth longitudinal MRI study
- 2022
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Ingår i: World Journal of Biological Psychiatry. - : Informa UK Limited. - 1562-2975 .- 1814-1412. ; 23:3, s. 201-207
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Tidskriftsartikel (refereegranskat)abstract
- Objectives: The effects of nature on physical and mental health are an emerging topic in empirical research with increasing influence on practical health recommendations. Here we set out to investigate the association between spending time outdoors and brain structural plasticity in conjunctions with self-reported affect. Methods: We established the Day2day study, which includes an unprecedented in-depth assessment of variability of brain structure in a serial sequence of 40–50 structural magnetic resonance imaging (MRI) acquisitions of each of six young healthy participants for 6–8 months (n = 281 MRI scans in total). Results: A whole-brain analysis revealed that time spent outdoors was positively associated with grey matter volume in the right dorsolateral prefrontal cortex and positive affect, also after controlling for physical activity, fluid intake, free time, and hours of sunshine. Conclusions: Results indicate remarkable and potentially behaviorally relevant plasticity of cerebral structure within a short time frame driven by the daily time spent outdoors. This is compatible with anecdotal evidence of the health and mood-promoting effects of going for a walk. The study may provide the first evidence for underlying cerebral mechanisms of so-called green prescriptions with possible consequences for future interventions in mental disorders.
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| 36. |
- Kühn, Simone, et al.
(författare)
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The dynamics of change in striatal activity following updating training
- 2013
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Ingår i: Human Brain Mapping. - : Wiley. - 1065-9471 .- 1097-0193. ; 34:7, s. 1530-1541
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Tidskriftsartikel (refereegranskat)abstract
- Increases in striatal activity have been suggested to mediate training-related improvements in working-memory ability. We investigated the temporal dynamics of changes in task-related brain activity following training of working memory. Participants in an experimental group and an active control group, trained on easier tasks of a constant difficulty in shorter sessions than the experimental group, were measured before, after about 1 week, and after more than 50 days of training. In the experimental group an initial increase of working-memory related activity in the functionally defined right striatum and anatomically defined right and left putamen was followed by decreases, resulting in an inverted u-shape function that relates activity to training over time. Activity increases in the striatum developed slower in the active control group, observed at the second posttest after more than 50 days of training. In the functionally defined left striatum, initial activity increases were maintained after more extensive training and the pattern was similar for the two groups. These results shed new light on the relation between activity in the striatum (especially the putamen) and the effects of working memory training, and illustrate the importance of multiple measurements for interpreting effects of training on regional brain activity.
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| 37. |
- Kuhn, Simone, et al.
(författare)
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The neural representation of intrusive thoughts
- 2013
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Ingår i: Social Cognitive and Affective Neuroscience. - : Oxford University Press (OUP). - 1749-5024 .- 1749-5016. ; 8:6, s. 688-693
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Tidskriftsartikel (refereegranskat)abstract
- Based on the philosophical notion that language embodies thought we investigated whether a habitual tendency for intrusive thought that younger and older participants report over a period of 100 sessions, spread out over about 6 months, is associated with brain regions related to language production. In favour of this hypothesis, we found that individual differences in habitual intrusive thoughts are correlated with activity in the left inferior frontal gyrus (IFG, Broca's area) as well as the cingulate cortex (CC) during a two-choice reaction-time task in fMRI. Participants who habitually tended to experience intrusive thoughts showed greater activity during task-free (baseline) compared to task periods in brain regions involved in language production. Task performance was unrelated to individual differences in intrusive thoughts. We conclude that intrusive thoughts may be represented in a language-like format and that individuals reporting a habitually higher tendency for intrusive thoughts may have stronger and more habitual inner speech processes.
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| 38. |
- Kumar Maroju, Praveen, et al.
(författare)
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Attosecond pulse shaping using a seeded free-electron laser
- 2020
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Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 578, s. 386-391
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Tidskriftsartikel (refereegranskat)abstract
- Attosecond pulses are central to the investigation of valence- and core-electron dynamics on their natural timescales. The reproducible generation and characterization of attosecond waveforms has been demonstrated so far only through the process of high-order harmonic generation. Several methods for shaping attosecond waveforms have been proposed, including the use of metallic filters, multilayer mirrors and manipulation of the driving field. However, none of these approaches allows the flexible manipulation of the temporal characteristics of the attosecond waveforms, and they suffer from the low conversion efficiency of the high-order harmonic generation process. Free-electron lasers, by contrast, deliver femtosecond, extreme-ultraviolet and X-ray pulses with energies ranging from tens of microjoules to a few millijoules. Recent experiments have shown that they can generate subfemtosecond spikes, but with temporal characteristics that change shot-to-shot. Here we report reproducible generation of high-energy (microjoule level) attosecond waveforms using a seeded free-electron laser. We demonstrate amplitude and phase manipulation of the harmonic components of an attosecond pulse train in combination with an approach for its temporal reconstruction. The results presented here open the way to performing attosecond time-resolved experiments with free-electron lasers.
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| 39. |
- Lisofsky, Nina, et al.
(författare)
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Hippocampal volume and functional connectivity changes during the female menstrual cycle.
- 2015
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Ingår i: NeuroImage. - : Elsevier BV. - 1095-9572 .- 1053-8119. ; 118, s. 154-162
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Tidskriftsartikel (refereegranskat)abstract
- Hippocampal volume has been shown to be sensitive to variations in estrogen and progesterone levels across rodents' estrous cycle. However, little is known about the covariation of hormone levels and brain structure in the course of the human menstrual cycle. Here, we examine this covariation with a multi-method approach that includes several brain imaging methods and hormonal assessments. We acquired structural and functional scans from 21 naturally cycling women on four time points during their cycles (early follicular phase, late follicular phase, ovulation and luteal phase). Hormone blood concentrations and cognitive performance in different domains were assessed on each of the measurement occasions. Structural MRI images were processed by means of whole-brain voxel-based morphometry and FreeSurfer. With either method, bilateral increases in hippocampal volume were found in the late follicular phase relative to the early follicular phase. The gray matter probability in regions of hippocampal volume increase was associated with lower mean diffusivity in the same region. In addition, we observed higher functional connectivity between the hippocampi and the bilateral superior parietal lobe in the late follicular phase. We did not find any reliable cycle-related performance variations on the cognitive tasks. The present results show that hormonal fluctuations covary with hippocampal structure and function in the course of the human menstrual cycle.
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| 40. |
- Lövdén, Martin, et al.
(författare)
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Experience-dependent plasticity of white-matter microstructure extends into old age
- 2010
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Ingår i: Neuropsychologia. - : Elsevier BV. - 0028-3932 .- 1873-3514. ; 48:13, s. 3878-3883
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Tidskriftsartikel (refereegranskat)abstract
- Experience-dependent alterations in the human brain's white-matter microstructure occur in early adulthood, but it is unknown whether such plasticity extends throughout life. We used cognitive training, diffusion-tensor imaging (DTI), and structural MRI to investigate plasticity of the white-matter tracts that connect the left and right hemisphere of the frontal lobes. Over a period of about 180 days, 20 younger adults and 12 older adults trained for a total of one hundred and one 1-h sessions on a set of three working memory, three episodic memory, and six perceptual speed tasks. Control groups were assessed at pre- and post-test. Training affected several DTI metrics and increased the area of the anterior part of the corpus callosum. These alterations were of similar magnitude in younger and older adults. The findings indicate that experience-dependent plasticity of white-matter microstructure extends into old age and that disruptions of structural interhemispheric connectivity in old age, which are pronounced in aging, are modifiable by experience and amenable to treatment.
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