Florian Metzger

Altered frontal brain oxygenation in detoxified alcohol dependent patients with unaffected verbal fluency performance.

Despite prominent prefrontal deficits and alterations in anatomy, neurophysiology, and neuropsychology after long-term alcohol consumption in alcohol dependent patients, only a few investigations of functional brain activity have been published. Using functional near-infrared spectroscopy (fNIRS), we examined the concentration changes in oxygenated (O(2)Hb) and deoxygenated (HHb) haemoglobin in 17 right-handed alcohol dependent patients after detoxification and 17 matched healthy controls during a verbal fluency task. Alcohol dependent patients were characterized by normal behavioural performance (number of words produced) and physiological activation patterns (increase of O(2)Hb and decrease of HHb) over frontotemporal regions during phonological and semantical verbal fluency. However, the degree of activation was diminished (lower magnitude of oxygenation) and the localization of the activation was more restricted to inferior frontal areas as compared with the healthy participants. fNIRS is a sensitive and valid method, to detect alterations in brain functioning in clinical groups like alcohol dependent patients. Altered prefrontal functional brain activation during verbal fluency in alcohol dependent patients in a detoxified state may precede behavioural or cognitive alterations with a later onset.

Pushing the performance of Biased Neighbor Selection through Biased Unchoking

Locality promotion in P2P content distribution networks is currently a major research topic. One of the goals of all discussed approaches is to reduce the interdomain traffic that causes high costs for ISPs. However, the focus of the work in this field is generally on the type of locality information that is provided to the overlay and on the entities that exchange this information. An aspect that is mostly neglected is how this information is used by the peers. In this paper, we consider the predominant approach of Biased Neighbor Selection and compare it with Biased Unchoking, which is an alternative locality aware peer selection strategy that we propose in this paper. We show that both mechanisms complement each other for the BitTorrent file sharing application and achieve the best performance when combined.

Vagus somatosensory evoked potentials--a possibility for diagnostic improvement in patients with mild cognitive impairment?.

Objective: Vagus somatosensory evoked potentials (VSEP) are far-field potentials probably generated in nuclei of then. vagus in the lower brainstem. They represent a putative, easily applicable method for discrimination between patients with Alzheimer’s disease (AD), patients with mild cognitive impairment (MCI), and healthy controls (HC). Methods: Thirteen patients with AD, 12 with MCI, and 27 age- and gender-matched HC were investigated by stimulating the cutaneous branch of the n. vagus; 8, 6, and 20, respectively, were included in the main part of the analysis. Results: In fronto-central recordings (electrode positions Fz-F4) a grading from HC over MCI to AD could be found, with a significant linear trend over the three groups and significantly increased latencies of the cognitively impaired patients but no significant difference between MCI and AD. Conclusion: The results indicate that the method of VSEP is able to discriminate between cognitively declined patients and HC, whereas no clear-cut differences were detected between MCI and AD.

Auricular vagus somatosensory evoked potentials in vascular dementia

A new method for the assessment of vagus nerve function has recently been introduced into clinical practice. In the present study we could show that, contrary to our results in Alzheimer’s disease (AD), in patients with vascular dementia (VaD) vagus sensory evoked potentials (VSEP) did not show statistically significant differences as compared to healthy controls. Thus, we hypothesize that the new method of VSEP could possibly contribute to a differential diagnosis between early cases of AD and VaD.

TCP video streaming and mobile networks

The rise in popularity of TCP-based video streaming in recent years is unbroken. These streaming services not just operate on wired access lines but more and more specifically target users of mobile networks as well. Yet it still remains difficult to evaluate the performance of such streaming approaches in mobile networks. This is especially critical as mobile networks exhibit much more potential for undesirable interactions between the network protocol layers and control plane properties on one side and the protocols and strategies of the application layer on the other side, ultimately resulting in scenarios with bad QoE for video streaming.This paper aims to rectify this lack of knowledge and understanding in a multi-pronged approach as follows: The first contribution provides an easy means to investigate such interactions with a streaming simulation framework built on ns-3. In a second contribution three exemplary scenarios within this framework are investigated in order to uncover the nature of such interactions. The final undertaking attempts to unravel the issues of the mobility scenario using context information. Such information can be collected through crowdsensing and collaboratively processed in a Big Data approach. This results in a tailor-made analytical solution through the formulation of a Mixed Integer Linear Program (MILP) that can prevent video stalling in this particular scenario.

Vagus somatosensory evoked potentials are delayed in Alzheimer’s disease, but not in major depression

In Alzheimer’s disease (AD), the degeneration of brainstem nuclei is different from major depression (MD). Thus, vagus somatosensory evoked potentials (VSEP) proposed for the functional assessment of brainstem nuclei should show prolonged latencies in AD but not in MD. In 55 AD patients, 57 MD patients and two age-matched control groups evoked potentials were recorded upon stimulation of the auricular branch of the vagus nerve. In the AD, not in the MD group, latencies were significantly longer as compared to controls. Thus, the method of VSEP could contribute to the important differential diagnosis of AD and MD in elderly patients.

Aberrant functional connectivity in depression as an index of state and trait rumination

Depression has been shown to be related to a variety of aberrant brain functions and structures. Particularly the investigation of alterations in functional connectivity (FC) in major depressive disorder (MDD) has been a promising endeavor, since a better understanding of pathological brain networks may foster our understanding of the disease. However, the underling mechanisms of aberrant FC in MDD are largely unclear. Using functional near-infrared spectroscopy (fNIRS) we investigated FC in the cortical parts of the default mode network (DMN) during resting-state in patients with current MDD. Additionally, we used qualitative and quantitative measures of psychological processes (e.g., state/trait rumination, mind-wandering) to investigate their contribution to differences in FC between depressed and non-depressed subjects. Our results indicate that 40% of the patients report spontaneous rumination during resting-state. Depressed subjects showed reduced FC in parts of the DMN compared to healthy controls. This finding was linked to the process of state/trait rumination. While rumination was negatively correlated with FC in the cortical parts of the DMN, mind-wandering showed positive associations.

Functional brain imaging of walking while talking – An fNIRS study

Since functional imaging of whole body movements is not feasible with functional magnetic resonance imaging (fMRI), the present study presents in vivo functional near-infrared spectroscopy (fNIRS) as a suitable technique to measure body movement effects on fronto-temporo-parietal cortical activation in single- and dual-task paradigms. Previous fNIRS applications in studies addressing whole body movements were typically limited to the assessment of prefrontal brain areas. The current study investigated brain activation in the frontal, temporal and parietal cortex of both hemispheres using functional near-infrared spectroscopy (fNIRS) with two large 4×4 probe-sets with 24 channels each during single and dual gait tasks. 12 young healthy adults were measured using fNIRS walking on a treadmill: the participants performed two single-task (ST) paradigms (walking at different speeds, i.e. 3 and 5km/h) and a dual task (DT) paradigm where a verbal fluency task (VFT) had to be executed while walking at 3km/h. The results show an increase of activation in Brocas area during the more advanced conditions (ST 5km/h vs. ST 3km/h, DT vs. ST 3km/h, DT vs. 5km/h), while the corresponding area on the right hemisphere was also activated. DT paradigms including a cognitive task in conjunction with whole body movements elicit wide-spread cortical activation patterns across fronto-temporo-parietal areas. An elaborate assessment of these activation patterns requires more extensive fNIRS assessments than the traditional prefrontal investigations, e.g. as performed with portable fNIRS devices.

Brain activation in frontotemporal and Alzheimer’s dementia: a functional near-infrared spectroscopy study

BackgroundFrontotemporal dementia is an increasingly studied disease, the underlying functional impairments on a neurobiological level of which have not been fully understood. Patients with the behavioral-subtype frontotemporal dementia (bvFTD) are particularly challenging for clinical measurements such as functional imaging due to their behavioral symptoms. Here, an alternative imaging method, functional near-infrared spectroscopy (fNIRS), is introduced to measure task-related cortical brain activation based on blood oxygenation. The current study investigated differences in cortical activation patterns of patients with bvFTD, Alzheimer’s dementia (AD), and healthy elderly subjects measured by fNIRS.MethodEight probable bvFTD patients completed the semantic, phonological, and control conditions of a verbal fluency task. Eight AD patients and eight healthy controls were compared on the same task. Simultaneously, an fNIRS measurement was conducted and analyzed using a correction method based on the expected negative correlation between oxygenated and deoxygenated hemoglobin.ResultsHealthy controls show an increase in cortical activation measured in frontoparietal areas such as the dorsolateral prefrontal cortex. The activation pattern of patients with AD is similar, but weaker. In contrast, bvFTD patients show a more frontopolar pattern, with activation of Broca’s area, instead of the dorsolateral prefrontal cortex and the superior temporal gyrus. The frontoparietal compensation mechanisms, seen in the healthy elderly, were missing in bvFTD patients.ConclusionDifferent frontoparietal cortical activation patterns may indicate a correlate of diverse pathophysiological mechanisms of AD and bvFTD during verbal fluency processing. The AD pattern is weaker and more similar to the healthy pattern, whereas the bvFTD pattern is qualitatively different, namely more frontopolar and without frontoparietal compensation activation. It adheres to a change of cortical activation during the course of the disease.

Analysis of web-based video delivery

The recent shift from specialized video streaming solutions to user-friendly Web-based video delivery platforms has attracted large audiences to these platforms. However, this could also result in future bandwidth bottlenecks and a degradation of network parameters if traffic demands continue to rise. Due to the reliable TCP protocol the influence of network degradations expresses itself only in the playback and buffering behavior of the media player but not in a loss of video quality. In this paper, we describe and conduct performance measurements of the YouTube platform as the largest representative of Web video delivery platforms. First we give insights into the composition of its architecture. Then we describe the video streaming process for which we present models of the clients approaches to video stream buffering and playback control. Afterwards the performance of Web streaming is evaluated using this model in a network emulator. We find that YouTubes rate limiting provides sufficient QoE to the user during good network conditions, but degrades fast with increased packet loss and latency.