Institute Homepage
Institute Homepage EN Sign In

Publications

DEPARTMENTS

Emperical Interference

Haptic Intelligence

Modern Magnetic Systems

Perceiving Systems

Physical Intelligence

Robotic Materials

Social Foundations of Computation

Research Groups

Autonomous Vision

Autonomous Learning

Bioinspired Autonomous Miniature Robots

Dynamic Locomotion

Embodied Vision

Human Aspects of Machine Learning

Intelligent Control Systems

Learning and Dynamical Systems

Locomotion in Biorobotic and Somatic Systems

Micro, Nano, and Molecular Systems

Movement Generation and Control

Neural Capture and Synthesis

Physics for Inference and Optimization

Organizational Leadership and Diversity

Probabilistic Learning Group

Topics

Robot Learning

Conference Paper

2022

Autonomous Learning

Robotics

AI

Career

Award

Book Auditory cues for attention management Glatz, C. 51:158, MPI Series in Biological Cybernetics, Logos Verlag, Berlin, Germany, 2018
{An exhaustible supply of mental resources necessitate that we are selective for what we attend to. Attention prioritizes what ought to be processed and what ignored, allocating valuable resources to selected information at the cost of unattended information elsewhere. For this purpose it is necessary to know the conditions that help the brain decide when attention should be paid, where to and to what information. This dissertation shows how auditory cues can support the management of limited attentional resources based on auditory characteristics. Auditory cues can increase the overall alertness, orient attention to unattended information, or manage attentional resources by informing of an upcoming task-switch and, therefore, indicate when to pay attention to which task.}
BibTeX
Article Autofocusing-based phase correction Loktyushin, A., Ehses, P., Schölkopf, B., Scheffler, K. {Magnetic Resonance in Medicine}, 80(3):958-968, Wiley-Liss, New York, 2018
{Purpose Phase artifacts due to B0 inhomogeneity can severely degrade the quality of MR images. The artifacts are particularly prominent in long-TE scans and usually appear as ghosting and blur. We propose a retrospective phase correction method based on autofocusing. The proposed method uses raw data acquired with standard imaging sequences, and does not rely on navigators or external measures of field inhomogeneity. Methods We formulate and solve the optimization problem, where we seek the latent phase offsets that are associated with an optimal value of the image quality measure that is evaluated in the spatial domain. As a quality measure we use entropy computed on spatial image gradients. We propose two types of objective function, both compatible with parallel imaging and accelerated image acquisition. Results We evaluate the method on both synthetic and real data. In real data case we evaluate the performance on a range of sequences and images acquired with different acceleration factors. The experimental results demonstrate that our method is capable of minimizing ghosting artifacts and that the quality of the output images is similar to navigator-based reconstructions. Conclusion The presented technique can be alternative to or complement navigator-based methods, and is able to improve images with severe phase artifacts from all standard imaging sequences.}
DOI BibTeX
Miscellaneous Banto: a free participant recruitment and booking system de la Rosa, S. TeaP 2018: Abstracts of the 60th Conference of Experimental Psychologists, 54, Pabst Science Publishers, Lengerich, Germany, 2018
{Many psychological experiments require human participants for which researchers often need to share the same equipment (computers, fMRI scanners, etc.). As a result recruitment of participants is a time consuming task that requires coordination between researchers. Here we present a new free online tool for participant recruitment called Banto that manages participant recruitment and equipment booking. Banto was partially developed with the help of the Department of Perception, Cognition and Action at the Max Planck Institute of Biological Cybernetics, T\"ubingen, Germany. Banto works like an online posting board: experimenters post their experiments and participants sign up for them. Once a participant signs up for an experiment appointment, all equipment that experimenters specified as necessary for the experiment (e.g. computers, rooms) is automatically booked along. While Banto is free to use we ask users to support the project by claiming some overhead costs for participant recruitment in future grant applications.}
DOI BibTeX
Miscellaneous Bilateral Direct Electrical Stimulation (DES-) and Neural Event Triggered (NET-) fMRI in the Macaque Anterior Insula Smuda, J. 2018 BibTeX
Article Binocular rivalry transitions predict inattention symptom severity in adult ADHD Jusyte, A., Zaretskaya, N., Höhnle, N., Bartels, A., Schönenberg, M. {European Archives of Psychiatry and Clinical Neuroscience}, 268(4):373-382, 2018
{Attention deficit and hyperactivity disorder (ADHD) is a prevalent childhood disorder that is often maintained throughout the development and persists into adulthood. Established etiology models suggest that deficient inhibition underlies the core ADHD symptoms. While experimental evidence for impaired motor inhibition is overwhelming, little is known about the sensory inhibition processes, their changes throughout the development, and the relationship to ADHD symptoms. Here, we used the well-established binocular rivalry (BR) paradigm to investigate for the very first time the inhibitory processes related to visual perception in adults with ADHD. In BR, perception alternates between two dichoptically presented images throughout the viewing period, with shorter dominant percept durations and longer transition periods indicating poorer suppression/inhibition. Healthy controls (N \textequals 28) and patients with ADHD (N \textequals 32) were presented with two dissimilar images (orthogonal gratings) separately to each eye through a mirror stereoscope and asked to report their perceptual experiences. There were no differences between groups in any of the BR markers. However, an association between transition durations and symptom severity emerged in the ADHD group. Importantly, an exploratory multiple regression analysis revealed that inattention symptoms were the sole predictor for the duration of transition periods. The lack of impairments to sensory inhibition in adult, but not pediatric ADHD may reflect compensatory changes associated with development, while a correlation between inhibition and inattention symptoms may reveal an invariant core of the disorder.}
DOI BibTeX
Article Biological foundations and beneficial effects of trance Hove, M., Stelzer, J. {Behavioral and Brain Sciences}, 41:26-27, 2018
{Singh proposes a cultural evolutionary theory of shamanic practices, including trance. We argue that cultural factors are deeply intertwined with biological aspects in shaping shamanic practices, and the underlying biology is critical. We discuss the neural underpinnings of rhythm-induced trance, how they can facilitate insight, and how altered states can promote healing.}
DOI BibTeX
Ph.D. Thesis Biophysical Simulation of the Functional Magnetic Resonance Signal Formation in Realistic Neurovascular Networks Báez-Yáñez, M. Eberhard-Karls-Universität Tübingen, Tübingen, Germany, 2018 BibTeX
Miscellaneous Bipartite connectivity mapping (BCM) Lohmann, G., Stelzer, J., Scheffler, K. Sixth Biennial Conference on Resting-State and Brain Connectivity, 2018 BibTeX
Article Body size estimation of self and others in females varying in BMI Thaler, A., Geuss, M., Mölbert, S., Giel, K., Streuber, S., Romero, J., Black, M., Mohler, B. {PLoS One}, 13(2):1-24, Public Library of Science, San Francisco, CA, 2018
{Previous literature suggests that a disturbed ability to accurately identify own body size may contribute to overweight. Here, we investigated the influence of personal body size, indexed by body mass index (BMI), on body size estimation in a non-clinical population of females varying in BMI. We attempted to disentangle general biases in body size estimates and attitudinal influences by manipulating whether participants believed the body stimuli (personalized avatars with realistic weight variations) represented their own body or that of another person. Our results show that the accuracy of own body size estimation is predicted by personal BMI, such that participants with lower BMI underestimated their body size and participants with higher BMI overestimated their body size. Further, participants with higher BMI were less likely to notice the same percentage of weight gain than participants with lower BMI. Importantly, these results were only apparent when participants were judging a virtual body that was their own identity (Experiment 1), but not when they estimated the size of a body with another identity and the same underlying body shape (Experiment 2a). The different influences of BMI on accuracy of body size estimation and sensitivity to weight change for self and other identity suggests that effects of BMI on visual body size estimation are self-specific and not generalizable to other bodies.}
DOI BibTeX
Article Body-relative horizontal-vertical anisotropy in human representations of traveled distances Hinterecker, T., Pretto, P., de Winkel, K., Karnath, H., Bülthoff, H., Meilinger, T. {Experimental Brain Research}, 236(10):2811-2827, Springer-Verlag, Heidelberg, 2018
{A growing number of studies investigated anisotropies in representations of horizontal and vertical spaces. In humans, compelling evidence for such anisotropies exists for representations of multi-floor buildings. In contrast, evidence regarding open spaces is indecisive. Our study aimed at further enhancing the understanding of horizontal and vertical spatial representations in open spaces utilizing a simple traveled distance estimation paradigm. Blindfolded participants were moved along various directions in the sagittal plane. Subsequently, participants passively reproduced the traveled distance from memory. Participants performed this task in an upright and in a 30\mbox{$^\circ$} backward-pitch orientation. The accuracy of distance estimates in the upright orientation showed a horizontal\textendashvertical anisotropy, with higher accuracy along the horizontal axis compared with the vertical axis. The backward-pitch orientation enabled us to investigate whether this anisotropy was body or earth-centered. The accuracy patterns of the upright condition were positively correlated with the body-relative (not the earth-relative) coordinate mapping of the backward-pitch condition, suggesting a body-centered anisotropy. Overall, this is consistent with findings on motion perception. It suggests that the distance estimation sub-process of path integration is subject to horizontal\textendashvertical anisotropy. Based on the previous studies that showed isotropy in open spaces, we speculate that real physical self-movements or categorical versus isometric encoding are crucial factors for (an)isotropies in spatial representations.}
DOI BibTeX
Article Brain amyloid-burden and cerebrovascular disease are synergistically associated with neurometabolism in cognitively unimpaired older adults Schreiner, S., Kirchner, T., Narkhede, A., Wyss, M., Van Bergen, J., Steininger, S., Gietl, A., Leh, S., Treyer, V., Buck, A., Pruessmann, K., Nitsch, R., Hock, C., Henning, A., Brickman, A., Unschuld, P. {Neurobiology of Aging}, 63:152-161, 2018
{Alzheimer\textquotesingles disease (AD) is the most common cause for cognitive dysfunction at high age. In AD, pathological hallmarks such as beta-amyloid (A\ss) aggregation and also neurometabolic change, as indicated by altered myo-inositol (mI) and N-acetylaspartate (NAA) levels, typically precede manifestation of cognitive dysfunction by years. While cerebrovascular disease occurs at earliest stages of AD pathogenesis, the interplay between vascular and neurometabolic brain change is largely unknown. Thirty cognitively normal elderly persons (age\textequals70$\pm$5.6 years, MMSE\textequals29.2$\pm$1) received 11-C-Pittsburgh Compound B PET for estimating A\ss-plaque density, 7 Tesla (7T) fluid-attenuated inversion recovery MRI for quantifying white matter hyperintensity volume, and high-resolution FIDLOVS-based magnetic resonance spectroscopic imaging (MRSI) at 7T to investigate tissue-specific neurometabolism in the posterior cingulate and precuneus (PCP). Beta-amyloid (\ss\textequals0.45, p\textequals0.018) and white matter hyperintensities (\ss\textequals0.40, p\textequals0.046) were independently and interactively (\ss\textequals -0.49, p\textequals0.026) associated with a higher ratio of mI over NAA (mI/NAA) in PCP gray matter but not in white matter. Our data suggest that cerebrovascular disease and A\ss burden are synergistically related to AD-related gray matter neurometabolism at high age.}
DOI BibTeX
Miscellaneous Bursting behavior in sparse random networks of excitatory and inhibitory neurons Vinogradov, O. Third Workshop on Advanced Methods in Theoretical Neuroscience (WANMTN 2018), 2018 BibTeX
Miscellaneous Bursting behavior in sparse random networks of excitatory and inhibitory neurons Vinogradov, O., Sukenik, N., Moses, E., Levina, A. Bernstein Conference 2018, 2018
{Network bursting is the most common type of spontaneous activity of dissociated neuronal cultures [1,2]. The frequency, length, amplitude, and shape of bursts vary substantially depending on the culture preparation, age, environment, and cellular composition [3]. Most of the models proposed to explain network bursting explicitly included components that drive bursting behavior, such as feedback, adaptation, or synaptic fatigue [4,5,6,7]. However, it is not clear whether such specific components are a necessary prerequisite of bursting activity. In the current study, we show that bursting occurs as one of the spontaneous dynamical states of a sparse random network of excitatory and inhibitory leaky Integrate-and-fire neurons with delta synapses. This type of network models is one of the most simple candidates to study the behavior of dissociated neuronal cultures. Yet, previously described synchronous states of such network models are not reconcilable with experimental observations [8]. These states have a relatively high frequency of global oscillations or show only a small amount of network synchrony. We investigated the behavior of the model outside of the typically studied parameter-intervals and found that population bursting appears in networks with strong synapses and very slow external Poisson input. In this specific region of the parameters space, the system shows slow bistable dynamics. The network spontaneously fluctuates between almost quiescent asynchronous state and fast synchronous firing. This transition closely resembles the network bursting in neuronal cultures. Our model displays a variety of burst\textquoterights shapes, amplitudes, and frequencies, some of which exhibit a clear parameter dependence. For instance, we demonstrate that the frequency of bursts depends on the coupling strength and relative strength of inhibitory synapses. Finally, we show that this type of dynamics is preserved in networks of different sizes when the synaptic strength is scaled proportionally 1K$\surd$. Overall, our model suggests that the sparse random network of excitatory and inhibitory neurons can exhibit various types of network bursting activity on the mesoscopic level. This concept can further extend mechanistic understanding of the variability of bursting dynamics in living neuronal cultures.}
DOI BibTeX
Article Causal Inference in the Perception of Verticality de Winkel, K., Katliar, M., Diers, D., Bülthoff, H. {Scientific Reports}, 8:1-12, 2018
{The perceptual upright is thought to be constructed by the central nervous system (CNS) as a vector sum; by combining estimates on the upright provided by the visual system and the body\textquoterights inertial sensors with prior knowledge that upright is usually above the head. Recent findings furthermore show that the weighting of the respective sensory signals is proportional to their reliability, consistent with a Bayesian interpretation of a vector sum (Forced Fusion, FF). However, violations of FF have also been reported, suggesting that the CNS may rely on a single sensory system (Cue Capture, CC), or choose to process sensory signals based on inferred signal causality (Causal Inference, CI). We developed a novel alternative-reality system to manipulate visual and physical tilt independently. We tasked participants (n \textequals 36) to indicate the perceived upright for various (in-)congruent combinations of visual-inertial stimuli, and compared models based on their agreement with the data. The results favor the CI model over FF, although this effect became unambiguous only for large discrepancies ($\pm$60\mbox{$^\circ$}). We conclude that the notion of a vector sum does not provide a comprehensive explanation of the perception of the upright, and that CI offers a better alternative.}
DOI BibTeX
Miscellaneous Challenges in estimating T1 Relaxation Times of Macromolecules in the Human Brain at 9.4T Murali-Manohar, S., Wright, A., Henning, A. MRS Workshop 2018 Metabolic Imaging, 2018
{In order to determine the T1 relaxation times of the metabolites in human brain including the ones that have either shorter T2 relaxation times or represent J-coupled spin systems, shorter TE times have to be chosen where there is a significant macromolecular contribution. Therefore, the behaviour of macromolecules (MMs) and their relaxation have to be understood clearly. In [1] the T1 relaxation time of the macromolecular baseline has been determined as a whole using single inversion recovery but values have not been provided for individual MMs, in [2] it has been estimated for the MM peak at 0.93 ppm. Here we attempt to understand the T1 relaxation pattern for the individual macromolecules at 9.4T in the human brain with a double inversion recovery (DIR) technique in order to measure the relaxation of individual MM components which relax at different rates and uniquely impact the overlying metabolite spectrum in traditional excitation approaches.}
BibTeX
Article Change, stability, and instability in the Pavlovian guidance of behaviour from adolescence to young adulthood Moutoussis, M., Bullmore, E., Goodyer, I., Fonagy, P., Jones, P., Dolan, R., Dayan, P. {PLoS Computational Biology}, 14(12):1-26, Public Library of Science, San Francisco, CA, 2018
{Pavlovian influences are important in guiding decision-making across health and psychopathology. There is an increasing interest in using concise computational tasks to parametrise such influences in large populations, and especially to track their evolution during development and changes in mental health. However, the developmental course of Pavlovian influences is uncertain, a problem compounded by the unclear psychometric properties of the relevant measurements. We assessed Pavlovian influences in a longitudinal sample using a well characterised and widely used Go-NoGo task. We hypothesized that the strength of Pavlovian influences and other \textquoteleftpsychomarkers\textquoteright guiding decision-making would behave like traits. As reliance on Pavlovian influence is not as profitable as precise instrumental decision-making in this Go-NoGo task, we expected this influence to decrease with higher IQ and age. Additionally, we hypothesized it would correlate with expressions of psychopathology. We found that Pavlovian effects had weak temporal stability, while model-fit was more stable. In terms of external validity, Pavlovian effects decreased with increasing IQ and experience within the task, in line with normative expectations. However, Pavlovian effects were poorly correlated with age or psychopathology. Thus, although this computational construct did correlate with important aspects of development, it does not meet conventional requirements for tracking individual development. We suggest measures that might improve psychometric properties of task-derived Pavlovian measures for future studies.}
DOI BibTeX
Miscellaneous Changes of inferred functional connectivity under subsampling Hasanpour, M., Massobrio, P., Levina, A. Bernstein Conference 2018, 2018
{Studies of anatomical and functional connectivity lay down a basis for our understanding of the brain networks [1]. On a macroscale the measures are based on the coarse observations that allow capturing major connection tracts in the brain. However, on mesoscale and microscale, derivation of the networks\textquoteright connectivity have to rely on observation form a tiny fraction of the system. The inference of the whole network properties thus has to be done by extrapolation from the observed set to an unobserved one [2]. Our primary goal here is to understand how to make this inference rigorously. Network science\textquoteright tools describe relevant network properties, but so far it is not known how the subsampling alters them. One of centrally used observables to characterize brain network is a small-worldness index: an average clustering coefficient divided by a diameter of the network. In a set of different network classes (random, small-word, scale-free) we demonstrate analytically and numerically that the average local clustering coefficient is preserved by subsampling (Figure A). Therefore changes in the small-worldness under subsampling is driven by changes in the inferred diameter. We observe that the diameter is strongly influenced by the subsampling thus our inference of small-worldness without correction for the sample size is biased. As next step, we are aiming at finding regularities in diameter changes under subsampling. The brain networks have a highly complex structure, that is not captured by the simple random networks we consider in theoretical studies. To account for it, we investigate functional networks extracted from the developed cultures using High-Density Multi-Electrode Array (HD-MEA). We pre-process the recordings using SpiCoDyn package [3] and employ transfer entropy (TE) as a measure capturing information flow [4]. We define functional connectivity by conventional thresholding the TE matrix at the level of one standard deviation above the mean. We consider different window-subsampling of the full HD-MEA (Figure B). The threshold for significant functional connections depends on the sampled set (Figure C). Thus the network inferred from the subsampling of the whole system differs from the subnetwork with the same nodes inferred from the complete recordings. Next, we are going to study how the difference in thresholding alters our inference of the underlying network properties and how we can define a more sampling-independent thresholding strategy.}
DOI BibTeX
Article Characterization of macromolecular baseline of human brain using metabolite cycled semi-LASER at 9.4T Giapitzakis, I., Avdievich, N., Henning, A. {Magnetic Resonance in Medicine}, 80(2):462-473, 2018
{Purpose Macromolecular resonances (MM) arise mainly from cytosolic proteins and overlap with metabolites, influencing metabolite quantification. Macromolecules can serve as valuable biomarkers for diseases and pathologies. The objectives of this study were to characterize MM at 9.4T in the human brain (occipital and left parietal lobe) and to describe the RF coil setup used for MM acquisition in the two regions. Methods An adiabatic inversion pulse was optimised for metabolite nulling at 9.4T using double inversion recovery and was combined for the first time with metabolite cycled (MC) semi-LASER and appropriate coil configuration. MM spectra (seven volunteers) from two brain locations were averaged and smoothed creating MM templates, which were then parametrized using simulated Voigt-shaped lines within LCModel. Quantification was performed on individual data sets, including corrections for different tissue composition and the T1 and T2 relaxation of water. Results Our coil configuration method resulted in efficient math formula (\textgreater30 T/$\surd$kW) for both brain regions. The 15 MM components were detected and quantified in MM baselines of the two brain areas. No significant differences in concentration levels of MM between different regions were found. Two new MM peaks were reported (M7 M8). Conclusion Double inversion, which was combined with MC semi-LASER, enabled the acquisition of high spectral resolution MM spectra for both brain regions at 9.4T. The 15 MM components were detected and quantified. Two new MM peaks were reported for the first time (M7 M8) and preliminarily assigned to $\beta$-methylene protons of aspartyl-groups.}
DOI BibTeX
Article Chemical exchange saturation transfer MRI contrast in the human brain at 9.4 T Zaiss, M., Schuppert, M., Deshmane, A., Herz, K., Ehses, P., Füllbier, L., Lindig, T., Bender, B., Ernemann, U., Scheffler, K. {NeuroImage}, 179:144-155, Academic Press, Orlando, FL, 2018
{PURPOSE: The high chemical shift separation at 9.4 T allows for selective saturation of proton pools in exchange with water protons. For the first time, highly selective and comprehensive chemical exchange saturation transfer (CEST) experiments were performed in the human brain at 9.4 T. This work provides insight into CEST signals in the human brain in comparison with existing animal studies, as well as with CEST effects in vivo at lower field strengths. METHODS: A novel snapshot-CEST method for human brain scans at 9.4 T was optimized and employed for highly-spectrally-resolved (95 offsets) CEST measurements in healthy subjects and one brain tumor patient. Reproducibility and stability between scans was verified in grey and white matter after B0, B1, and motion correction of the acquired 3D CEST volumes. Two-step Lorentzian fitting was used to further improve separation of spectrally discernible signals to create known and novel CEST contrast maps at 9.4 T. RESULTS: At a saturation power of B1 \textequals 0.5 $\mu$T most selective CEST effects could be obtained in the human brain with high inter-scan reproducibility. While contrast behavior of previously measured signals at lower field, namely amide-, guanidyl- and NOE-CEST effects, could be reproduced, novel signals at 2.7 ppm, and -1.6 ppm could be verified in healthy subjects and in a brain tumor patient for the first time. CONCLUSION: High spectral resolution chemical exchange saturation transfer at 9.4 T allows deeper insights into the Z-spectrum structure of the human brain, and provides many different contrasts showing different correlations in healthy tissue and in tumor-affected areas of the brain, generating hypotheses for future investigations of in-vivo-CEST at UHF.}
DOI BibTeX
Miscellaneous Clinical CEST MRI studies at ultra-high B0 field (7T and 9.4T) Zaiss, M. 7th International Workshop on Chemical Exchange Saturation Transfer (CEST 2018), 69, 2018
{CEST benefits of ultra-high fields due to the better frequency separation(1,2). However, is this just a benefit for the interested MR scientist or is this also of use to address clinical questions? This can only be answered if CEST measurements of humans are performed at 7T or even 9.4T both available for human scans. While judgment about clinical benefits require larger studies, CEST in humans at UHF brings interesting preliminary insights and strong hypothesis generation.}
BibTeX
Miscellaneous Collaborative Spatial Search within Walkable Virtual Environments: the Influence of Global Reference Information Hanrieder, M., Kaiser, K., Hatzipanayioti, A., Mohler, B., Meilinger, T. TeaP 2018: Abstracts of the 60th Conference of Experimental Psychologists, 101, Pabst Science Publishers, Lengerich, Germany, 2018
{Collaborative spatial search is an important task, for example, when firefighters or rescue teams search for victims within a building. In two experiments we examined the distinction between individual and collaborative search and the influence of common reference information on these two types of search. In Experiment 1, individuals and dyads were asked to walk through and fully cover virtual city environments of varied complexity displayed on head mounted displays. We recorded search time and missed locations. With increasing environmental size and resultant increasing memory load participants missed more target locations. Dyads showed longer added trajectories than individuals, but less self-overlap with their own trajectory (i.e., walking the same section multiple times). This suggests that the between-trajectories-overlap between searchers was responsible for the inefficient trajectories in collaborative search. In Experiment 2, we provided participants with a compass to facilitate organization of their searches. However, results were similar to those of Experiment 1. Mere orientation cues without a-priori environmental information seem insufficient to divide the search task and improve search performance.}
DOI BibTeX
Miscellaneous Collaborative vs Individual Problem Solving Hatzipanayioti, A., Bechtold, M., Mohler, B., Bülthoff, H., Meilinger, T. 16th European Workshop on Imagery and Cognition: From World to Mind: Images and Representations (EWIC 2018), 41, 2018
{In everyday life we come across numerous problem solving situations that we either resolve alone or in collaboration with another person. The aim of the present study was to examine the underlying cognitive mechanisms that are involved in collaborative problem solving using virtual reality technology. Participants worked either individually or in pairs (collaborative condition) to solve a virtual rubik\textquoterights cube type puzzle task. The puzzle-task included 9 cubes with different colours on different sides and a solution space with 4 empty cube positions. Participants were instructed to choose the correct cubes among the distractor ones and arrange them within the solution space such that each side of the solution space displayed a single color. In the collaborative condition participants stood opposite to each other, allowing for communication, and each person was represented within the virtual world by a virtual head and a virtual controller. Results showed that participants were faster in solving the task when they were working in pairs compared to individually. Moreover, they employed a strategy of dividing the cube space according to their physical position in space. Our conjecture is that pairs, given their location in space, had access to all relevant information of the problem at a single point in time, compared to individuals. That is, together they could view all sides and all colors of the solution space, whereas individuals had to remember the color of cubes that were not visible from their perspective (i.e. the back side of the solution space). In this interpretation access from multiple perspectives at once, as in the collaborative condition allows for better problem solving. In a follow up experiment, we are currently testing whether collaborative problem solving from adjacent problem solvers is similar to individual performance.}
BibTeX
Miscellaneous Collaborative vs. Individual Problem Solving Hatzipanayioti, A., Bechtold, M., Mohler, B., Bülthoff, H., Meilinger, T. 11th International Conference on Spatial Cognition (SC 2018), 2018 BibTeX
Article Combination of surface and "vertical" loop elements improves receive performance of a human head transceiver array at 9.4 T Avdievich, N., Giapitzakis, I., Pfrommer, A., Borbath, T., Henning, A. {NMR in Biomedicine}, 31(2):1-13, 2018
{Ultra-high-field (UHF, $\geq$7 T) human magnetic resonance imaging (MRI) provides undisputed advantages over low-field MRI ($\leq$3 T), but its development remains challenging because of numerous technical issues, including the low efficiency of transmit (Tx) radiofrequency (RF) coils caused by the increase in tissue power deposition with frequency. Tight-fit human head transceiver (TxRx) arrays improve Tx efficiency in comparison with Tx-only arrays, which are larger in order to fit multi-channel receive (Rx)-only arrays inside. A drawback of the TxRx design is that the number of elements in an array is limited by the number of available high-power RF Tx channels (commonly 8 or 16), which is not sufficient for optimal Rx performance. In this work, as a proof of concept, we developed a method for increasing the number of Rx elements in a human head TxRx surface loop array without the need to move the loops away from a sample, which compromises the array Tx performance. We designed and constructed a prototype 16-channel tight-fit array, which consists of eight TxRx surface loops placed on a cylindrical holder circumscribing a head, and eight Rx-only vertical loops positioned along the central axis (parallel to the magnetic field B0) of each TxRx loop, perpendicular to its surface. We demonstrated both experimentally and numerically that the addition of the vertical loops has no measurable effect on the Tx efficiency of the array. An increase in the maximum local specific absorption rate (SAR), evaluated using two human head voxel models (Duke and Ella), measured 3.4 or less. At the same time, the 16-element array provided 30 improvement of central signal-to-noise ratio (SNR) in vivo relative to a surface loop eight-element array. The novel array design also demonstrated an improvement in the parallel Rx performance in the transversal plane. Thus, using this method, both the Rx and Tx performance of the human head array can be optimized simultaneously.}
DOI BibTeX
Article Combined PET/MRI: Global Warming: Summary Report of the 6th International Workshop on PET/MRI, March 27-29, 2017, Tübingen, Germany Bailey, D., Pichler, B., Gückel, B., Antoch, G., Barthel, H., Bhujwalla, Z., Biskup, S., Biswal, S., Bitzer, M., Boellaard, R., Braren, R., Brendle, C., Brindle, K., Chiti, A., la Fougère, C., Gillies, R., Goh, V., Goyen, M., Hacker, M., Heukamp, L., et al. {Molecular Imaging and Biology}, 20(1):4-20, 2018
{The 6th annual meeting to address key issues in positron emission tomography (PET)/magnetic resonance imaging (MRI) was held again in T\"ubingen, Germany, from March 27 to 29, 2017. Over three days of invited plenary lectures, round table discussions and dialogue board deliberations, participants critically assessed the current state of PET/MRI, both clinically and as a research tool, and attempted to chart future directions. The meeting addressed the use of PET/MRI and workflows in oncology, neurosciences, infection, inflammation and chronic pain syndromes, as well as deeper discussions about how best to characterise the tumour microenvironment, optimise the complementary information available from PET and MRI, and how advanced data mining and bioinformatics, as well as information from liquid biomarkers (circulating tumour cells and nucleic acids) and pathology, can be integrated to give a more complete characterisation of disease phenotype. Some issues that have dominated previous meetings, such as the accuracy of MR-based attenuation correction (AC) of the PET scan, were finally put to rest as having been adequately addressed for the majority of clinical situations. Likewise, the ability to standardise PET systems for use in multicentre trials was confirmed, thus removing a perceived barrier to larger clinical imaging trials. The meeting openly questioned whether PET/MRI should, in all cases, be used as a whole-body imaging modality or whether in many circumstances it would best be employed to give an in-depth study of previously identified disease in a single organ or region. The meeting concluded that there is still much work to be done in the integration of data from different fields and in developing a common language for all stakeholders involved. In addition, the participants advocated joint training and education for individuals who engage in routine PET/MRI. It was agreed that PET/MRI can enhance our understanding of normal and disrupted biology, and we are in a position to describe the in vivo nature of disease processes, metabolism, evolution of cancer and the monitoring of response to pharmacological interventions and therapies. As such, PET/MRI is a key to advancing medicine and patient}
DOI BibTeX
Article Comparison of B0 versus B0 and B1 field inhomogeneity correction for glycosaminoglycan chemical exchange saturation transfer imaging Müller-Lutz, A., Lijmani, A., Stabinska, J., Zaiss, M., Boos, J., Wittsack, H. {Magnetic Resonance Materials in Physics, Biology and Medicine}, 31(5):645-651, No longer published by Elsevier, Amsterdam, 2018
{Purpose The study compares glycosaminoglycan chemical exchange saturation transfer (gagCEST) imaging of intervertebral discs corrected for solely B0 inhomogeneities or both B0 and B1 inhomogeneities. Methods Lumbar intervertebral discs of 20 volunteers were examined with T2-weighted and gagCEST imaging. Field inhomogeneity correction was performed with B0 correction only and with correction of both B0 and B1. GagCEST effects measured by the asymmetric magnetization transfer ratio (MTRasym) and signal-to-noise ratio (SNR) were compared between both methods. Results Significant higher MTRasym and SNR values were obtained in the nucleus pulposus using B0 and B1 correction compared with B0-corrected gagCEST. The GagCEST effect was significantly different in the nucleus pulposus compared with the annulus fibrosus for both methods. Conclusion The B0 and B1 field inhomogeneity correction method leads to an improved quality of gagCEST imaging in IVDs compared with only B0 correction.}
DOI BibTeX
Miscellaneous Comparison of the BOLD hemodynamic response function at 3T and 9.4T Ress, D., Kim, J., Taylor, A., Scheffler, K., Hagberg, G., Himmelbach, M. 48th Annual Meeting of the Society for Neuroscience (Neuroscience 2018), 2018
{Ultra-high-field (UHF) functional magnetic resonance imaging (fMRI) has shown tremendous potential for advancing non-invasive neuroscience in the human brain. To enable analysis of fMRI data at UHF, we need to measure the hemodynamic response function (HRF) at UHF and compare it to that obtained at conventional field strengths. Methods: 2-s duration visual stimulation consisted of round regions of flickering colored dots that appear for 0.67 s, followed by a second differently colored region of dots at a second location, then a third. Subjects (N \textequals 6) had to push a button with the color matching the dot display, a fast-paced and moderately demanding task. Each stimulus was followed by a 28-s period during which subjects performed a slow-paced color-detection task at fixation. 16 stimuli were presented per run, and 5 runs per session. fMRI data were collected using a point-spread-function-corrected EPI sequence that obtained 1.5-mm voxels at 3T, 1-mm at 9.4T, both at 1.25-s TR. We averaged the BOLD response across the 80 stimulus presentations to measure the HRF in visual cortex (V1), superior colliculus (SC), and lateral geniculate nucleus (LGN). Results: Good quality HRFs were measured in all regions at both field strengths (Figure, upper row). Cortical HRFs always had significant undershoots, but these were not observed in subcortical regions. No significant \textquotedblleftinitial dips\textquotedblright were observed. In V1, time-to-peak for 9.4T HRFs was significantly longer, 6.77$\pm$0.28 s, then was observed at 3T, 5.51$\pm$0.25 s (Figure, lower row). Subcortical HRFs were significantly faster than in cortex, but again 9.4T HRFs were slower (LGN 5.18$\pm$0.16 s, SC 4.77$\pm$0.22 s) than those measured at 3T (LGN 4.54$\pm$0.19 s, SC 4.08$\pm$0.19 s). Conclusions: HRFs recorded at UHF exhibit significantly slower temporal dynamics than at 3T. Also, sub-cortical HRFs are significantly faster than those observed in cortex, with minimal undershoot. Analysis of UHF and sub-cortical fMRI needs to take these differences into account to permit accurate linear analysis of experimental results.}
BibTeX
Miscellaneous Comparison of two alternative sequences for human in-vivo brain MR Current Density Imaging (MRCDI) Göksu, C., Hanson, L., Siebner, H., Ehses, P., Scheffler, K., Thielscher, A. Joint Annual Meeting ISMRM-ESMRMB 2018, 2018
{MRCDI is a novel technique, utilizing different phase-sensitive MR methods for non-invasive measurements of weak currents in the human body, which is important in several neuroscience applications. Here, we compare the in-vivo performance of two different MR methods, multi-echo spin echo (MESE) and steady-state free precession free induction decay (SSFP-FID), with single- vs. multi-gradient-echo readouts. We demonstrate that multi-gradient-echo readouts improve both methods. We validate the linear dependence of the measured current-induced magnetic field on the injected current strength for both methods, and propose the more efficient SSFP-FID method as being well suited for highly sensitive single-slice human in-vivo MRCDI.}
BibTeX
Book Chapter Complex Role of the Serotonin Receptors in Depression: Implications for Treatment Amidfar, M., Colic, L., Walter, M., Kim, Y. In Understanding Depression: Volume 1. Biomedical and Neurobiological Background, 83-95, Springer, Singapore, 2018
{Evidence from pharmacological, neuroimaging, postmortem, and genetic studies underlines the various roles of 5-HT receptor subtypes in the pathogenesis of major depressive disorder. Recent investigations further supported the notion of their interaction with the antidepressant medication and advanced the knowledge on underlying mechanisms of their action. The heterogeneous properties of individual 5-HT receptors offer a chance for development of new generation of antidepressants, which may be more beneficial and effective than traditional selective serotonin reuptake inhibitors (SSRIs). Antagonists of 5-HT2A, 5-HT2C, 5-HT3, 5-HT6, and 5-HT7 receptors, as well as agonists of 5-HT1A, 5-HT1B, 5-HT2C, 5-HT4, and 5-HT6 receptors, were observed to produce antidepressant-like responses. Paradoxical antidepressant-like effects of both agonists and antagonists of 5-HT receptors are likely connected to the diverse neurochemical mechanisms they instantiate. Augmented behavioral effects of SSRIs and other antidepressants used in combined treatment with 5-HT receptor agonists or antagonists have also been reported. The involvement of 5-HT receptors in depression is complex. Identifying the role of 5-HT receptors in response to antidepressants is an essential step in recognizing their mechanisms of action and, thereby, potentially producing more effective antidepressants with fewer side effects in patients with major depressive disorder.}
DOI BibTeX
Article Compressed sensing for high-resolution nonlipid suppressed 1H FID MRSI of the human brain at 9.4T Nassirpour, S., Chang, P., Avdievitch, N., Henning, A. {Magnetic Resonance in Medicine}, 80(6):2311-2325, Wiley-Liss, New York, 2018
{Purpose The aim of this study was to apply compressed sensing to accelerate the acquisition of high resolution metabolite maps of the human brain using a nonlipid suppressed ultra-short TR and TE 1H FID MRSI sequence at 9.4T. Methods X-t sparse compressed sensing reconstruction was optimized for nonlipid suppressed 1H FID MRSI data. Coil-by-coil x-t sparse reconstruction was compared with SENSE x-t sparse and low rank reconstruction. The effect of matrix size and spatial resolution on the achievable acceleration factor was studied. Finally, in vivo metabolite maps with different acceleration factors of 2, 4, 5, and 10 were acquired and compared. Results Coil-by-coil x-t sparse compressed sensing reconstruction was not able to reliably recover the nonlipid suppressed data, rather a combination of parallel and sparse reconstruction was necessary (SENSE x-t sparse). For acceleration factors of up to 5, both the low-rank and the compressed sensing methods were able to reconstruct the data comparably well (root mean squared errors [RMSEs] $\leq$ 10.5 for Cre). However, the reconstruction time of the low rank algorithm was drastically longer than compressed sensing. Using the optimized compressed sensing reconstruction, acceleration factors of 4 or 5 could be reached for the MRSI data with a matrix size of 64 $\times$ 64. For lower spatial resolutions, an acceleration factor of up to R$\sim$4 was successfully achieved. Conclusion By tailoring the reconstruction scheme to the nonlipid suppressed data through parameter optimization and performance evaluation, we present high resolution (97 $\micro$L voxel size) accelerated in vivo metabolite maps of the human brain acquired at 9.4T within scan times of 3 to 3.75 min.}
DOI BibTeX
Article Constrained optimization for position calibration of an NMR field camera Chang, P., Nassirpour, S., Eschelbach, M., Scheffler, K., Henning, A. {Magnetic Resonance Imaging}, 80(1):380-390, 2018
{Purpose: Knowledge of the positions of field probes in an NMR field camera is necessary for monitoring the B0 field. The typical method of estimating these positions is by switching the gradients with known strengths and calculating the positions using the phases of the FIDs. We investigated improving the accuracy of estimating the probe positions and analyzed the effect of inaccurate estimations on field monitoring. Methods: The field probe positions were estimated by 1) assuming ideal gradient fields, 2) using measured gradient fields (including nonlinearities), and 3) using measured gradient fields with relative position constraints. The fields measured with the NMR field camera were compared to fields acquired using a dual-echo gradient recalled echo B0 mapping sequence. Comparisons were done for shim fields from second- to fourth-order shim terms. Results: The position estimation was the most accurate when relative position constraints were used in conjunction with measured (nonlinear) gradient fields. The effect of more accurate position estimates was seen when compared to fields measured using a B0 mapping sequence (up to 10\textendash15 more accurate for some shim fields). The models acquired from the field camera are sensitive to noise due to the low number of spatial sample points. Conclusion Position estimation of field probes in an NMR camera can be improved using relative position constraints and nonlinear gradient fields.}
DOI BibTeX
Article Continuous Subjective Rating of Perceived Motion Incongruence During Driving Simulation Cleij, D., Venrooij, J., Pretto, P., Pool, D., Mulder, M., Bülthoff, H. {IEEE Transactions on Human-Machine Systems}, 48(1):17-29, 2018
{Motion cueing algorithms are used in motion simulation to map the inertial vehicle motion onto the limited simulator motion space. This mapping causes mismatches between the unrestricted visual motion and the constrained inertial motion, which results in perceived motion incongruence (PMI). It is still largely unknown what exactly causes visual and inertial motion in a simulator to be perceived as incongruent. Current methods for measuring motion incongruence during motion simulation result in time-invariant measures of the overall incongruence, which makes it difficult to determine the relevance of the individual and short-duration mismatches between visual and inertial motion cues. In this paper, a novel method is presented to subjectively measure the time-varying PMI continuously throughout a simulation. The method is analyzed for reliability and validity of its measurements, as well as for its applicability in relating physical short-duration cueing errors to PMI. The analysis shows that the method is reliable and that the results can be used to obtain a deeper insight into the formation of motion incongruence during driving simulation.}
DOI BibTeX
Article Coordination Properties of GdDO3A-Based Model Compounds of Bioresponsive MRI Contrast Agents Gunduz, S., Vibhute, S., Botar, R., Kalman, F., Toth, I., Tircsó, G., Regueiro-Figueroa, M., Esteban-Gomez, D., Platas-Iglesias, C., Angelovski, G. {Inorganic Chemistry}, 57(10):5973-5986, 2018
{We report a detailed characterization of the thermodynamic stability and dissociation kinetics of Gd3+ complexes with DO3A derivatives containing a (methylethylcarbamoylmethylamino)acetic acid (L1), (methylpropylcarbamoylmethylamino)acetic acid (L2), 2-dimethylamino-N-ethylacetamide (L3), or 2-dimethylamino-N-propylacetamide (L4) group attached to the fourth nitrogen atom of the macrocyclic unit. These ligands are model systems of Ca2+- and Zn2+-responsive contrast agents (CA) for application in magnetic resonance imaging (MRI). The results of the potentiometric studies (I \textequals 0.15 M NaCl) provide stability constants with log KGdL values in the range 13.9\textendash14.8. The complex speciation in solution was found to be quite complicated due to the formation of protonated species at low pH, hydroxido complexes at high pH, and stable dinuclear complexes in the case of L1,2. At neutral pH significant fractions of the complexes are protonated at the amine group of the amide side chain (log KGdL$\times$H \textequals 7.2\textendash8.1). These ligands form rather weak complexes with Mg2+ and Ca2+ but very stable complexes with Cu2+ (log KCuL \textequals 20.4\textendash22.3) and Zn2+ (log KZnL \textequals 15.5\textendash17.6). Structural studies using a combination of 1H NMR and luminescence spectroscopy show that the amide group of the ligand is coordinated to the metal ion at pH $\sim$8.5, while protonation of the amine group provokes the decoordination of the amide O atom and a concomitant increase in the hydration number and proton relaxivity. The dissociation of the complexes occurs mainly through a rather efficient proton-assisted pathway, which results in kinetic inertness comparable to that of nonmacrocyclic ligands such as DTPA rather than DOTA-like complexes.}
DOI BibTeX
Modern Magnetic Systems Article Correction of axial position uncertainty and systematic detector errors in ptychographic diffraction imaging Loetgering, L., Rose, M., Keskinbora, K., Baluktsian, M., Dogan, G., Sanli, U., Bykova, I., Weigand, M., Schütz, G., Wilhein, T. {Optical Engineering}, 57(8), The Society, Redondo Beach, Calif., 2018 DOI BibTeX
Miscellaneous Correlation between APT-CEST and 18F-Choline PET in glioma at 3T Rega, M., Torrealdea, F., Hearle, J., Zaiss, M., Carvalho, A., Asaf, A., Punwani, S., Golay, X., Dickson, J., Shankar, A., Hyare, H. Joint Annual Meeting ISMRM-ESMRMB 2018, 2018
{Chemical exchange saturation transfer MRI is emerging as a powerful diagnostic tool and has been shown to correlate with glioma tumour grade and molecular genetics. In this study, we aim to investigate whether APT signal is a non-invasive biomarker of Teenage and Young Adult glioma cell proliferation through correlation with 18F-Cho PET SUV as the gold standard. The strong positive correlation found in APT and 18F-Cho PET SUV indirectly demonstrates that APT SI may be a marker of glioma cell proliferation and further demonstrates the potential of APT in the assessment of glioma burden.}
BibTeX
Miscellaneous Critical avalanches in a spatially structured model of cortical On-Off dynamics Zeraati, R., Engel, T., Levina, A. Bernstein Conference 2018, 2018
{Cortical activity is permeated with endogenously generated fluctuations that affect responses to sensory stimuli and correlate with behavioral variability. These ongoing dynamics have been studied on two different spatial scales. On a local scale of single cortical columns, ongoing activity spontaneously transitions between episodes of vigorous (On) and faint (Off) spiking, synchronously across cortical layers. Dynamics of these local On-Off transitions are modulated during goal-directed behavior and predict behavioral performance [1]. On a wider spatial scale of interacting cortical columns, spontaneous activity propagates as cascades of bursts known as neural avalanches. The size of these avalanches is well approximated by a power-law distribution, suggesting that brain operates close to a critical point [2], which was shown to be optimal for information processing [3,4]. Whether and how local On-Off dynamics can coexist with critical avalanches in the same network is still an open question. To investigate this question, we developed a branching model capable of capturing both the local On-Off dynamics and the propagation of neural avalanches on a wider spatial scale. Each unit in the model represents a cortical column, with a spatially structured connectivity to other units mimicking the cortex spatial organization. The columns spontaneously transition between On and Off episodes driven by a self-excitation, excitatory inputs from the neighboring columns, and by stochastic external inputs. On and Off episode durations in our model follow exponential distributions, similar to the On-Off dynamics observed in single cortical columns (Fig 1C) [1]. We examined under what conditions these local On-Off dynamics are consistent with the propagation of critical avalanches. We found that models with local connectivity do not exhibit critical dynamics in the limit of a large system size. In a critical model, the cut-off of the avalanche-size distribution is expected to scale with the system size. In contrast, in models with only nearest-neighbor connectivity, the cut-off stays constant for systems larger than some characteristic size-scale. We demonstrate that the scaling property can be recovered with a larger radius of connections or by rewiring a small fraction of local connections to long-range random connections (Fig 1D-E). Our results highlight the possible role of long-range connections in the cortex in defining the operating regime of the brain dynamics.}
DOI BibTeX
Article Crystal structure of 8-(4-methyl­phen­yl)-2′-de­oxy­adenosine hemihydrate Ardhapure, A., Sanghvi, Y., Borozdina, Y., Kapdi, A., Schulzke, C. {Acta Crystallographica Section E: Crystallographic Communications}, 74(1):1-5, 2018
{In the asymmetric unit, equalling the unit cell (triclinic, P1, Z \textequals 1), two mol­ecules of the title compound, 8-(4-methyl­phen­yl)-D-2′-de­oxy­adenosine, C17H19N5O3, are present, with distinct conformations of the two sugar moieties, together with one solvent water mol­ecule. All three ribose O atoms are involved in hydrogen bonding and the crystal packing is largely determined by hydrogen-bonding or hydrogen\textendashheteroatom inter­actions (O\textemdashH...O, O\textemdashH...N, N\textemdashH...O, C\textemdashH...O and C\textemdashH...N) with one independent mol­ecule directly linked to four neighbouring mol­ecules and the other mol­ecule directly linked to six neighbouring mol­ecules. The two independent mol­ecules of the asymmetric unit display three weak intra­molecular C\textemdashH-to-heteroatom contacts, two of which are very similar despite the different conformations of the deoxyribosyl moieties. The aromatic ring systems of both mol­ecules are in proximity to each other and somehow aligned, though not coplanar. The absolute structures of the two mol­ecules were assumed with reference to the reactant 8-bromo-D-2′-de­oxy­adenosine as they could not be determined crystallographically.}
DOI BibTeX
Modern Magnetic Systems Article Current-induced skyrmion generation through morphological thermal transitions in chiral ferromagnetic heterostructures Lemesh, I., Litzius, K., Böttcher, M., Bassirian, P., Kerber, N., Heinze, D., Zázvorka, J., Büttner, F., Caretta, L., Mann, M., Weigand, M., Finizio, S., Raabe, J., Im, M., Stoll, H., Schütz, G., Dupé, B., Kläui, M., Beach, G. S. D. {Advanced Materials}, 30(49), Wiley-VCH, Weinheim, 2018 DOI BibTeX
Article Data Visualization using Linear and Non-linear Dimensionality Reduction Methods Kim, J., Youn, J. {Journal of the Korea Society of Computer and Information}, 23(12):21-26, 2018
{As the large amount of data can be efficiently stored, the methods extracting meaningful features from big data has become important. Especially, the techniques of converting high- to low-dimensional data are crucial for the \textquoterightData visualization\textquoteright. In this study, principal component analysis (PCA; linear dimensionality reduction technique) and Isomap (non-linear dimensionality reduction technique) are introduced and applied to neural big data obtained by the functional magnetic resonance imaging (fMRI). First, we investigate how much the physical properties of stimuli are maintained after the dimensionality reduction processes. We moreover compared the amount of residual variance to quantitatively compare the amount of information that was not explained. As result, the dimensionality reduction using Isomap contains more information than the principal component analysis. Our results demonstrate that it is necessary to consider not only linear but also nonlinear characteristics in the big data analysis.}
DOI BibTeX
Miscellaneous Decoding the direction of implied motion in human early visual cortex Altan, G., Bartels, A. 48th Annual Meeting of the Society for Neuroscience (Neuroscience 2018), 2018
{Implied motion perception is a striking case of our capacity to infer motion features from static pictures that imply movement. At a higher, cognitive level, the mere configuration of an object (such as a snapshot of a walking human) can imply motion in a directional way. Previous studies have shown that implied motion processing recruits direction selective neurons and activates cortical motion processing regions. However, it is unknown whether object-processing regions or early visual regions are involved in implied motion processing. In the present study we used fMRI and multivariate pattern classification to examine which human brain regions differentiate implicit direction information in static images of implied motion. We hence examined BOLD ac­tivity patterns within independently defined early visual (V1-V3), motion (V5+/MT+) and object-processing (LO1, LO2) regions when participants viewed still images with directional implied motion (rightward vs. leftward). The stimuli contained both animate (birds) and inanimate (airplanes, cars) objects as sources of implied motion. The objects were presented at the center of the visual field on a horizontally blurred background in the periphery. We found that response patterns in visual areas V2, V3, human motion complex V5+/MT+, and object responsive region LO2 coded for the direction of the implied motion stimuli significantly better than chance. Decoding in visual areas V1 and LO1 was at chance level. We then examined decoding in retinotopically defined foveal and peripheral representations of V1-V3. Only the foveal representation was stimulated by the foreground objects, the periphery by blurred background. We found that peripheral V1-V3 allowed decoding of implied motion directions, while foveal representations did not. Hence, high-level information of implied motion directionality is represented in peripheral V1-V3, i.e. regions that were never given the information through bottom-up stimulation. This suggests that higher-level cognitive processes (potentially based in LO2, V5+/MT+) detect implied motion direction based on object configuration and feed it back to cover the peripheral context in early visual cortex, potentially encoding expected background-motion. The results provide direct evidence for information in early visual cortex originating from feedback, compatible with predictive coding theory.}
BibTeX
Article Decoding visual roughness perception: an fMRI study Kim, J., Bülthoff, I., Bülthoff, H. {Somatosensory \& Motor Research}, 35(3-4):212-217, 2018
{The neural substrates of tactile roughness perception have been investigated by many neuroimaging studies, while relatively little effort has been devoted to the investigation of neural representations of visually perceived roughness. In this human fMRI study, we looked for neural activity patterns that could be attributed to five different roughness intensity levels when the stimuli were perceived visually, i.e., in absence of any tactile sensation. During functional image acquisition, participants viewed video clips displaying a right index fingertip actively exploring the sandpapers that had been used for the behavioural experiment. A whole brain multivariate pattern analysis found four brain regions in which visual roughness intensities could be decoded: the bilateral posterior parietal cortex (PPC), the primary somatosensory cortex (S1) extending to the primary motor cortex (M1) in the right hemisphere, and the inferior occipital gyrus (IOG). In a follow-up analysis, we tested for correlations between the decoding accuracies and the tactile roughness discriminability obtained from a preceding behavioural experiment. We could not find any correlation between both although, during scanning, participants were asked to recall the tactilely perceived roughness of the sandpapers. We presume that a better paradigm is needed to reveal any potential visuo-tactile convergence. However, the present study identified brain regions that may subserve the discrimination of different intensities of visual roughness. This finding may contribute to elucidate the neural mechanisms related to the visual roughness perception in the human brain.}
DOI BibTeX
Article Decoupling of a double-row 16-element tight-fit transceiver phased array for human whole-brain imaging at 9.4 T Avdievich, N., Giapitzakis, I., Pfrommer, A., Shajan, G., Scheffler, K., Henning, A. {NMR in Biomedicine}, 31(9):1-13, Heyden & Son, London, 2018
{One of the major challenges in constructing multi-channel and multi-row transmit (Tx) or transceiver (TxRx) arrays is the decoupling of the array\textquotesingles loop elements. Overlapping of the surface loops allows the decoupling of adjacent elements and also helps to improve the radiofrequency field profile by increasing the penetration depth and eliminating voids between the loops. This also simplifies the design by reducing the number of decoupling circuits. At the same time, overlapping may compromise decoupling by generating high resistive (electric) coupling near the overlap, which cannot be compensated for by common decoupling techniques. Previously, based on analytical modeling, we demonstrated that electric coupling has strong frequency and loading dependence, and, at 9.4 T, both the magnetic and electric coupling between two heavily loaded loops can be compensated at the same time simply by overlapping the loops. As a result, excellent decoupling was obtained between adjacent loops of an eight-loop single-row (1 $\times$ 8) human head tight-fit TxRx array. In this work, we designed and constructed a 9.4-T (400-MHz) 16-loop double-row (2 $\times$ 8) overlapped TxRx head array based on the results of the analytical and numerical electromagnetic modeling. We demonstrated that, simply by the optimal overlap of array loops, a very good decoupling can be obtained without additional decoupling strategies. The constructed TxRx array provides whole-brain coverage and approximately 1.5 times greater Tx efficiency relative to a transmit-only/receive-only (ToRo) array, which consists of a larger Tx-only array and a nested tight-fit 31-loop receive (Rx)-only array. At the same time, the ToRo array provides greater peripheral signal-to-noise ratio (SNR) and better Rx parallel performance in the head\textendashfeet direction. Overall, our work provides a recipe for a simple, robust and very Tx-efficient design suitable for parallel transmission and whole-brain imaging at ultra-high fields.}
DOI BibTeX
Article Decoupling of a tight-fit transceiver phased array for human brain imaging at 9.4T: Loop overlapping rediscovered Avdievich, N., Giapitzakis, I., Pfrommer, A., Henning, A. {Magnetic Resonance in Medicine}, 79(2):1200-1211, 2018
{Purpose To improve the decoupling of a transceiver human head phased array at ultra-high fields (UHF, $\geq$ 7T) and to optimize its transmit (Tx) and receive (Rx) performance, a single-row eight-element (1 $\times$ 8) tight-fit transceiver overlapped loop array was developed and constructed. Overlapping the loops increases the RF field penetration depth but can compromise decoupling by generating substantial mutual resistance. Methods Based on analytical modeling, we optimized the loop geometry and relative positioning to simultaneously minimize the resistive and inductive coupling and constructed a 9.4T eight-loop transceiver head phased array decoupled entirely by overlapping loops. Results We demonstrated that both the magnetic and electric coupling between adjacent loops is compensated at the same time by overlapping and nearly perfect decoupling (below -30 dB) can be obtained without additional decoupling strategies. Tx-efficiency and SNR of the overlapped array outperformed that of a common UHF gapped array of similar dimensions. Parallel Rx-performance was also not compromised due to overlapping the loops. Conclusion As a proof of concept we developed and constructed a 9.4T (400 MHz) overlapped transceiver head array based on results of the analytical modeling. We demonstrated that at UHF overlapping loops not only provides excellent decoupling but also improves both Tx- and Rx-performance.}
DOI BibTeX
Miscellaneous Deep CEST MRI: 9.4T spectral super-resolution from 3T CEST MRI data Zaiss, M., Deshmane, A., Herz, K., Braun, M., Bender, B., Lindig, T., Scheffler, K. Joint Annual Meeting ISMRM-ESMRMB 2018, 2018
{CEST peaks are easy to detect at ultra-high-field strengths due to high signal and spectral separation. However, spectral coalescence and line broadening makes modeling of CEST effects at clinical field strengths (\textless\textequals3T) a challenge. In this proof-of-concept study of super-resolution CEST imaging, the underlying spectral features of 3T Z-spectra were predicted using a neural network trained on 9.4T data. Applying the neural network to untrained volunteer and patient data acquired at 3T resulted in the expected contrast in healthy gray and white matter and tumor tissue in Z-spectra and APT, NOE, and MT CEST maps.}
BibTeX
Conference Paper Deep Neural Network-Based Cooperative Visual Tracking Through Multiple Micro Aerial Vehicles Price, E., Lawless, G., Ludwig, R., Martinović, I., Bülthoff, H., Black, M., Ahmad, A. In {IEEE Robotics and Automation Letters}, 3:3193-3200, IEEE, Madrid, Spain, 2018
{Multi-camera tracking of humans and animals in outdoor environments is a relevant and challenging problem. Our approach to it involves a team of cooperating micro aerial vehicles (MAVs) with on-board cameras only. Deep neural networks (DNNs) often fail at detecting small-scale objects or those that are far away from the camera, which are typical characteristics of a scenario with aerial robots. Thus, the core problem addressed in this paper is how to achieve on-board, online, continuous and accurate vision-based detections using DNNs for visual person tracking through MAVs. Our solution leverages cooperation among multiple MAVs and active selection of most informative regions of image. We demonstrate the efficiency of our approach through simulations with up to 16 robots and real robot experiments involving two aerial robots tracking a person, while maintaining an active perception-driven formation. ROS-based source code is provided for the benefit of the community.}
DOI BibTeX
Article Delayed increase of thrombocyte levels after a single sub-anesthetic dose of ketamine: A randomized trial Colic, M., Woelfer, L., Colic, M., Leutritz, A., Liebe, T., Fensky, L., Sen, Z., Li, M., Hoffmann, J., Kretzschmar, M., Isermann, B., Walter, M. {European Neuropsychopharmacology}, 28(6):701-709, Elsevier, Amsterdam, 2018
{Recently, ketamine has been investigated as a potential antidepressant option for treatment resistant depression. Unlike traditional drugs, it yields immediate effects, most likely via increased glutamatergic transmission and synaptic plasticity. However, ketamine administration in humans is systemic and its long\textendashterm impact on blood parameters has not yet been described in clinical studies. Here we investigated potential sustained effects of ketamine administration (0.5 mg/kg ketamine racemate) on hematological and biochemical values in plasma and serum in a randomized double\textendashblinded study. 80 healthy young participants were included and whole blood samples were collected 5 days before, and 14 days after the infusion. To assess the group effect, repeated measure analyses of co\textendashvariance (rmANCOVA) were conducted for the following blood parameters: levels of sodium, potassium, calcium, hemoglobin and number of erythrocytes, lymphocytes, and thrombocytes. RmANCOVA revealed a significant time by treatment effect on thrombocyte levels (F1, 74 \textequals 13.54, p \textless 0.001, eta \textequals 0.155), driven by an increase in the ketamine group (paired t-test, t \textequals \textminus3.51, df \textequals 38, p \textequals 0.001). Specificity of thrombocyte effect was confirmed by logistic regression, and in addition, no other coagulation parameters showed significant interaction. Moreover, the relative increase in the ketamine group was stable across sexes and not predicted by age, BMI, smoking, alcohol or drug use, and contraception. Our results describe aftereffects of sub\textendashanesthetic ketamine administration on blood coagulation parameters, which should be considered especially when targeting psychiatric populations with relevant clinical comorbidities.}
DOI BibTeX
Conference Paper Design Guidelines for Reliability Communication in Autonomous Vehicles Faltaous, S., Baumann, M., Schneegass, S., Chuang, L. In AutomotiveUI \textquotesingle18: Proceedings of the 10th International Conference on Automotive User Interfaces and Interactive Vehicular Applications, 258-267, ACM Press, Toronto, ON, Canada, 2018 DOI BibTeX
Modern Magnetic Systems Article Deterministic creation and deletion of a single magnetic skyrmion observed by direct time-resolved X-ray microscopy Woo, S., Song, K. M., Zhang, X., Ezawa, M., Zhou, Y., Liu, X., Weigand, M., Finizio, S., Raabe, J., Park, M., Lee, K., Choi, J. W., Min, B., Koo, H. C., Chang, J. {Nature Electronics}, 1(5):288-296, Springer Nature, London, 2018 DOI BibTeX
Miscellaneous Differentiating between models of perceptual decision- making using pupil-size inferred confidence Kawaguchi, K. 19th Conference of Junior Neuroscientists of Tübingen (NeNa 2018), 2018 BibTeX
Modern Magnetic Systems Article Direct observation of Zhang-Li torque expansion of magnetic droplet solitons Chung, S., Tuan Le, Q., Ahlberg, M., Awad, A. A., Weigand, M., Bykova, I., Khymyn, R., Dvornik, M., Mazraati, H., Houshang, A., Jiang, S., Nguyen, T. N. A., Goering, E., Schütz, G., Gräfe, J., Åkerman, J. {Physical Review Letters}, 120(21), American Physical Society, Woodbury, N.Y., 2018
Magnetic droplets are nontopological dynamical solitons that can be nucleated in nanocontact based spin torque nano-oscillators (STNOs) with perpendicular magnetic anisotropy free layers. While theory predicts that the droplet should be of the same size as the nanocontact, its inherent drift instability has thwarted attempts at observing it directly using microscopy techniques. Here, we demonstrate highly stable magnetic droplets in all-perpendicular STNOs and present the first detailed droplet images using scanning transmission X-ray microscopy. In contrast to theoretical predictions, we find that the droplet diameter is about twice as large as the nanocontact. By extending the original droplet theory to properly account for the lateral current spread underneath the nanocontact, we show that the large discrepancy primarily arises from current-in-plane Zhang-Li torque adding an outward pressure on the droplet perimeter. Electrical measurements on droplets nucleated using a reversed current in the antiparallel state corroborate this picture.
DOI BibTeX