Title Participants Abstract "Analysis of an Interneuron Gamma Mechanism for Cross-Frequency Coupling" "Mojtaba Chehelcheraghi, Chie Nakatani, Cees van Leeuwen" "Signals with multiple oscillatory components may exhibit cross frequency coupling (CFC): a slow component modulating the amplitude and/or frequency of a fast one. CFC is ubiquitous in oscillatory brain signals but how it arises has remained unclear. We recently proposed a systematic approach to simulate CFC, in which all common modulations are generated by a Neural Mass Model 7. A key mechanism in this approach is the dynamic self-feedback circuit of the fast inhibitory interneuron population that generates Gamma band oscillatory activity. Depending on noise-input level, the circuit switches between a limit cycle regime enabling amplitude modulation and a resonance regime enabling frequency modulation. In this study, we analyze the behavior of this circuit, using the describing function method for the limit cycle regime and root locus analysis for the resonance regime. The relationship between circuit parameters and behavior is investigated by bifurcation analysis." "Influencing connectivity and cross-frequency coupling by real-time source localized neurofeedback of the posterior cingulate cortex reduces tinnitus related distress" "Sven Vanneste, Leen Joos, Jan Ost, Dirk De Ridder" "Background: In this study we are using source localized neurofeedback to moderate tinnitus related distress by influencing neural activity of the target region as well as the connectivity within the default network. Hypothesis: We hypothesize that up-training alpha and down-training beta and gamma activity in the posterior cingulate cortex has a moderating effect on tinnitus related distress by influencing neural activity of the target region as well as the connectivity within the default network and other functionally connected brain areas. Methods: Fifty-eight patients with chronic tinnitus were included in the study. Twenty-three tinnitus patients received neurofeedback training of the posterior cingulate cortex with the aim of up-training alpha and down-training beta and gamma activity, while 17 patients underwent training of the lingual gyrus as a control situation. A second control group consisted of 18 tinnitus patients on a waiting list for future tinnitus treatment. Results: This study revealed that neurofeedback training of the posterior cingulate cortex results in a significant decrease of tinnitus related distress. No significant effect on neural activity of the target region could be obtained. However, functional and effectivity connectivity changes were demonstrated between remote brain regions or functional networks as well as by altering cross frequency coupling of the posterior cingulate cortex. Conclusion: This suggests that neurofeedback could remove the information, processed in beta and gamma, from the carrier wave, alpha, which transports the high frequency information and influences the salience attributed to the tinnitus sound. Based on the observation that much pathology is the result of an abnormal functional connectivity within and between neural networks various pathologies should be considered eligible candidates for the application of source localized EEG based neurofeedback training. (c) 2016 The Authors. Published by Elsevier Inc." "From thoughtless awareness to effortful cognition: alpha - theta cross-frequency dynamics in experienced meditators during meditation, rest and arithmetic" "Kaat Alaerts" "Neural activity is known to oscillate within discrete frequency bands and the synchronization between these rhythms is hypothesized to underlie information integration in the brain. Since strict synchronization is only possible for harmonic frequencies, a recent theory proposes that the interaction between different brain rhythms is facilitated by transient harmonic frequency arrangements. In this line, it has been recently shown that the transient occurrence of 2:1 harmonic cross-frequency relationships between alpha and theta rhythms (i.e. falpha ≈ 12 Hz; ftheta ≈ 6 Hz) is enhanced during effortful cognition. In this study, we tested whether achieving a state of 'mental emptiness' during meditation is accompanied by a relative decrease in the occurrence of 2:1 harmonic cross-frequency relationships between alpha and theta rhythms. Continuous EEG recordings (19 electrodes) were obtained from 43 highly experienced meditators during meditation practice, rest and an arithmetic task. We show that the occurrence of transient alpha:theta 2:1 harmonic relationships increased linearly from a meditative to an active cognitive processing state (i.e. meditation " "Cross-frequency and band-averaged response variance prediction in the hybrid deterministic-statistical energy analysis method" "Edwin Reynders" "© 2018 The Authors The hybrid deterministic-statistical energy analysis method has proven to be a versatile framework for modeling built-up vibro-acoustic systems. The stiff system components are modeled deterministically, e.g., using the finite element method, while the wave fields in the flexible components are modeled as diffuse. In the present paper, the hybrid method is extended such that not only the ensemble mean and variance of the harmonic system response can be computed, but also of the band-averaged system response. This variance represents the uncertainty that is due to the assumption of a diffuse field in the flexible components of the hybrid system. The developments start with a cross-frequency generalization of the reciprocity relationship between the total energy in a diffuse field and the cross spectrum of the blocked reverberant loading at the boundaries of that field. By making extensive use of this generalization in a first-order perturbation analysis, explicit expressions are derived for the cross-frequency and band-averaged variance of the vibrational energies in the diffuse components and for the cross-frequency and band-averaged variance of the cross spectrum of the vibro-acoustic field response of the deterministic components. These expressions are extensively validated against detailed Monte Carlo analyses of coupled plate systems in which diffuse fields are simulated by randomly distributing small point masses across the flexible components, and good agreement is found." "A neural mass model of cross frequency coupling" "Mojtaba Chehelcheraghi, Cees van Leeuwen, Erik Steur, Chie Nakatani" "Electrophysiological signals of cortical activity show a range of possible frequency and amplitude modulations, both within and across regions, collectively known as cross-frequency coupling. To investigate whether these modulations could be considered as manifestations of the same underlying mechanism, we developed a neural mass model. The model provides five out of the theoretically proposed six different coupling types. Within model components, slow and fast activity engage in phase-frequency coupling in conditions of low ambient noise level and with high noise level engage in phase-amplitude coupling. Between model components, these couplings can be coordinated via slow activity, giving rise to more complex modulations. The model, thus, provides a coherent account of cross-frequency coupling, both within and between components, with which regional and cross-regional frequency and amplitude modulations could be addressed." "Efficiency of Conscious Access Improves with Coupling of Slow and Fast Neural Oscillations" "Chie Nakatani, Cees van Leeuwen" "Global workspace access is considered as a critical factor for the ability to report a visual target. A plausible candidate mechanism for global workspace access is coupling of slow and fast brain activity. We studied coupling in EEG data using cross-frequency phase–amplitude modulation measurement between delta/theta phases and beta/gamma amplitudes from two experimental sessions, held on different days, of a typical attentional blink (AB) task, implying conscious access to targets. As the AB effect improved with practice between sessions, theta–gamma and theta–beta coupling increased generically. Most importantly, practice effects observed in delta–gamma and delta–beta couplings were specific to performance on the AB task. In particular, delta–gamma coupling showed the largest increase in cases of correct target detection in the most challenging AB conditions. All these practice effects were observed in the right temporal region. Given that the delta band is the main frequency of the P3 ERP, which is a marker of global workspace activity for conscious access, and because the gamma band is involved in visual object processing, the current results substantiate the role of phase–amplitude modulation in conscious access to visual target representations." "Sliding Mode Control for Power Electronic Converters in Transmission andDistribution Grids- Applied to Three-Phase LCL-Filter Grid Coupling and Series Converteror UPFC" "Jan Verveckken" "With the introduction of wide-bandgap semiconductors, significantly higher switching frequencies are feasible for power electronic applications; computa- tional power to process the control algorithms is however not increasing with the same pace. Sliding mode controllers are known to have low computational demands and high robustness. Unlike continuous control methods, a sliding mode controller produces discrete control outputs, similar to the desired discrete switching behaviour of power electronics. This difference allows sliding mode control to combine two control levels, the external control level - where the application control goals are achieved, and the internal control - where the switching states of the power electronic converter are decided. We investigate if these controllers are able to reach state-of-the-art performance in power electronic applications in the distribution and transmission grid. Specifically, we investigate sliding mode control of three-phase LCL-filter grid connections and of a series converter of Unified Power Flow Controllers. In literature, the design of an LCL-filter for power electronic applications is based on recursive calculations and/or experience, with no guarantee of optimality. We adapt an analytic design method for analog filters in signal transmission to a grid-connection filter interpretation. Based on inductor design rules, we expand the method to incorporate the inherent impedances of power components as compared to the discrete components it was designed for. This allows us to optimise the controller analytically to any function of the filter components. We design an LCL-filter optimised for total life-cycle cost including the projected incurred power losses. Compared to other design methods, our resulting LCL- filter is significantly cheaper in the projected life cycle. Previous work did not yet design a sliding mode controller for a three-phase LCL-filter grid connection. Based on the dynamic model of an LCL-filter grid connection, we develop an external and internal sliding mode controller. The design method and tuning of the sliding mode controller is based on a single- phase model. Using a detailed three-phase model including the power-electronic switches we simulate the designed sliding mode controller. We compare the implementation of a three-phase abc and an equivalent two-phase αβ version. The two-phase implementation reduces competing switching decisions between the three phases, creating a more performant control under equal conditions. Previous work concerning the power flow control with a UPFC focusses on steady-state models of the control problem which results in lower dynamic performance. Complex cross-coupling compensations and tuning mechanisms fail to respond optimally to reference changes and create averse affects during unbalanced conditions. The internal power electronic aspects of the control issue are generally considered out of scope. Using dynamic power flow models and the instantaneous derivations, we isolate the key instantaneous system dynamics and develop a Dynamic Inverse Model Controller as well as a Direct Power Controller. The Inverse Model Controller is an continuous external controller combined with a sliding mode internal controller, the direct power controller is a combined external and internal sliding mode controller. Based on a detailed model of a UPFC equipped with a multi-level inverter, including power-electronic switches, we simulate the developed control systems under balanced and unbalanced conditions, while comparing their performance to continuous controllers from literature. Both developed controllers outperform the literature in balanced as well as unbalanced conditions, the Direct Power Controller having the best performance in all cases. In a scaled laboratory model with a multi-level inverter, we demonstrate the Direct Power Controller in balanced conditions. The congruence of the experimental and simulated results convinces us that we fully comprehend the control problem and demonstrate the performance of our developed controllers adequately. With this work we demonstrate that sliding mode control is an adequate control method for power-electronic applications. The design methodology explained in this work is easily adaptable to other converter topologies and various other applications. The totality of the work spans several types of control problems and demonstrates adequate solutions to each of them, easily transportable to other applications." "Multichannel feedforward control schemes with coupling compensation for active sound profiling" "Jaime Alberto Mosquera Sánchez, Wim Desmet" "Active sound profiling includes a number of control techniques that enables the equalization, rather than the mere reduction, of acoustic noise. Challenges may rise when trying to achieve distinct targeted sound profiles simultaneously at multiple locations, e.g., within a vehicle cabin. This paper introduces distributed multichannel control schemes for independently tailoring structural borne sound reaching a number of locations within a cavity. The proposed techniques address the cross interactions amongst feedforward active sound profiling units, which compensate for interferences of the primary sound at each location of interest by exchanging run-time data amongst the control units, while attaining the desired control targets. Computational complexity, convergence, and stability of the proposed multichannel schemes are examined in light of the physical system at which they are implemented. The tuning performance of the proposed algorithms is benchmarked with the centralized and pure-decentralized control schemes through computer simulations on a simplified numerical model, which has also been subjected to plant magnitude variations. Provided that the representation of the plant is accurate enough, the proposed multichannel control schemes have been shown as the only ones that properly deliver targeted active sound profiling tasks at each error sensor location. Experimental results in a 1:3-scaled vehicle mock-up further demonstrate that the proposed schemes are able to attain reductions of more than 60 dB upon periodic disturbances at a number of positions, while resolving cross-channel interferences. Moreover, when the sensor/actuator placement is found as defective at a given frequency, the inclusion of a regularization parameter in the cost function is seen to not hinder the proper operation of the proposed compensation schemes, at the time that it assures their stability, at the expense of losing control performance." "EEG alpha-theta (cross-frequency) dynamics during arithmetic performance, mind wandering and meditative states" "Neural oscillations have been shown to be functionally relevant for human behaviour. In this way, brain rhythms oscillating at different frequencies have been associated to different cognitive functions. Consequently, the interplay between brain rhythms in different frequency ranges (i.e. cross-frequency coupling) is thought to be essential for cognition to emerge. This thesis focuses on cross-frequency dynamics between EEG alpha (8-14 Hz) and theta (4-8 Hz) rhythms during different cognitive states. Specifically, it investigates the functional relevance of alpha:theta cross-frequency numerical ratios during arithmetic performance, mind wandering and meditative states. This approach to alpha-theta cross-frequency dynamics is based on a recent theory positing that the formation of different cross-frequency numerical ratios between the peak frequencies of two brain rhythms is reflective of their level of interaction. In this way, it is proposed that harmonic cross-frequency arrangements (e.g. 2:1 numerical ratio) would enable cross-frequency coupling. The rationale behind this premise is that only harmonic cross-frequency ratios allow stable and regular excitatory phase meetings between two neural populations (i.e. coincidence of time periods in which spiking is more likely to occur). The working hypothesis in this thesis was that alpha and theta rhythms would arrange more often in harmonic positions during both working memory tasks and mind wandering. This hypothesis was based on previous literature suggesting that alpha (8-14Hz) and theta (4-8 Hz) rhythms reflect different components of working memory that need to be integrated when information has to be stored and manipulated in the brain. This hypothesis was assessed throughout the four studies encompassing this thesis. In the first study (Chapter 2), we assess the incidence of different alpha:theta cross-frequency ratios during an arithmetic task with a strong working memory component, rest and meditation practice. It was shown that alpha and theta rhythms separated in the frequency domain during arithmetic performance (relative to rest and meditation) thereby increasing the incidence of cross-frequency numerical ratios between 2 and 3 (and therefore 2:1 and 3:1 phase synchrony). These changes were accompanied by a decreased occurrence of ratios between 1 and 1.6. Interestingly, the separation between alpha and theta rhythms in the frequency domain (i.e. increased occurrence of ratios around 2 and 3 and decreased occurrence of ratios between 1 and 1.6) were positively associated to arithmetic performance, thereby underlining their functional relevance. A similar pattern of results was observed in the second study (Chapter 3), in which the same paradigm was adopted but with participants that were highly experienced in meditation practice. In addition to the previously reported changes during arithmetic task (relative to rest and meditation practice), we report that meditation was associated to a decreased incidence of alpha:theta ratios between 2 and 3 and an increased incidence of alpha:theta ratios between 1 and 1.6 when compared to rest and arithmetic. Based on these latter results, it was speculated that these changes in alpha-theta cross-frequency dynamics could be attributed to reduced mind wandering during meditation. To further investigate the influence of meditation training in alpha:theta cross-frequency dynamics, we assessed in a third study (Chapter 4) whether the compliance to a meditation training course was significantly correlated to changes in the incidence of different alpha:theta cross-frequency ratios during meditation. In this way, we show that meditation training (i.e. minutes of attendance plus minutes of practice at home) was associated to an approximation of alpha and theta rhythms in the frequency domain (i.e. a decreased occurrence of alpha:theta cross-frequency ratios around 3 and an increased occurrence of cross-frequency ratios around 1.6). In line with the previous study, we speculated that these inter-individual differences in the incidence of different alpha:theta numerical ratios during mediation were associated to mind wandering. Finally, in the fourth study (Chapter 5) we directly assess whether the occurrence of different alpha:theta cross-frequency ratios were associated to mind wandering in the context of meditation practice. For this purpose, a sample of novice meditators were repeatedly interrupted during a breath focus meditation to report whether they were mind wandering or focusing on their breath. In line with previous findings, our results showed that mind wandering is associated to a separation of alpha and theta rhythms in the frequency domain (i.e. an increased incidence of alpha:theta ratios between 2 and 3 at the expense of the occurrence of alpha:theta ratios between 1 and 1.6). Together, our results consistently show a separation of alpha and theta rhythms in the frequency domain (higher mean alpha:theta numerical ratio) during both arithmetic performance (relative to rest) and mind wandering (in the context of meditation practice). Although these changes in alpha:theta cross-frequency ratios led to greater 2:1 and 3:1 harmonicity and phase synchrony between alpha and theta rhythms, the observed changes in the frequency architecture (as indexed by the incidence of different cross-frequency ratios) do not unequivocally reflect changes in the level of interaction between alpha (8-14Hz) and theta (4-8 Hz) rhythms. Therefore, we cannot conclude that here studied cognitive states involve different levels of communication between the neural populations that are entrained by neural oscillations in the alpha and theta range. In this way, changes in the incidence of different ratios cross-frequency ratios would remain descriptive and open to interpretation until future studies empirically disentangle whether: i) alpha and theta rhythms encompass two separate neural oscillations with exclusively sinusoidal properties and ii) different cross-frequency ratios reflect different levels of information exchange between neural rhythms. Regardless the interpretation we give to the incidence of different alpha:theta ratios, the here presented studies suggest the existence of a neurocognitive mechanism that supports both working memory task performance and mind wandering." "High-gamma oscillations precede visual steady-state responses : a human electrocorticography study" "Benjamin Wittevrongel, Elvira Khachatryan, Evelien Carrette, Marc M. Van Hulle"