KEYWORDS: Electroencephalography, Signal processing, Nonlinear optics, Field programmable gate arrays, Epilepsy, Network architectures, Biomedical optics, Nanotechnology, Current controlled current source, Very large scale integration
For processing of EEG signals, we propose a new architecture for the hardware emulation of discrete-time Cellular Nonlinear Networks (DT-CNN).
Our results show the importance of a high computational accuracy in EEG signal prediction that cannot be achieved with existing analogue VLSI circuits. The refined architecture of the processing elements and its resource schedule, the cellular network structure with local couplings, the FPGA-based embedded system containing the DT-CNN, and the data flow in the entire system will be discussed in detail.
The proposed DT-CNN design has been implemented and tested on an Xilinx FPGA development platform. The embedded co-processor with a multi-threading kernel is utilised for control and pre-processing tasks and data exchange to the host via Ethernet. The performance of the implemented DT-CNN has been determined for a popular example and compared to that of a conventional computer.
Approximately 1% of the world's population suffer from epileptic seizures throughout their lives that mostly come
without sign or warning. Thus, epilepsy is the most common chronical disorder of the neurological system. In the
past decades, the problem of detecting a pre-seizure state in epilepsy using EEG signals has been addressed in
many contributions by various authors over the past two decades. Up to now, the goal of identifying an impending
epileptic seizure with sufficient specificity and reliability has not yet been achieved. Cellular Nonlinear Networks
(CNN) are characterized by local couplings of dynamical systems of comparably low complexity. Thus, they
are well suited for an implementation as highly parallel analogue processors. Programmable sensor-processor
realizations of CNN combine high computational power comparable to tera ops of digital processors with low
power consumption. An algorithm allowing an automated and reliable detection of epileptic seizure precursors
would be a"huge step" towards the vision of an implantable seizure warning device that could provide information
to patients and for a time/event specific treatment directly in the brain. Recent contributions have shown that
modeling of brain electrical activity by solutions of Reaction-Diffusion-CNN as well as the application of a CNN
predictor taking into account values of neighboring electrodes may contribute to the realization of a seizure
warning device.
In this paper, a CNN based predictor corresponding to a spatio-temporal filter is applied to multi channel
EEG data in order to identify mutual couplings for different channels which lead to a enhanced prediction
quality. Long term EEG recordings of different patients are considered. Results calculated for these recordings
with inter-ictal phases as well as phases with seizures will be discussed in detail.
KEYWORDS: Brain, Epilepsy, Electroencephalography, Statistical analysis, Signal detection, Current controlled current source, Chromium, Nervous system, Time series analysis, Reliability
Epilepsy is the most common chronic disorder of the nervous system. Generally, epileptic seizures appear without foregoing sign or warning. The problem of detecting a possible pre-seizure state in epilepsy from EEG signals has been addressed by many authors over the past decades. Different approaches of time series analysis of brain electrical activity already are providing valuable insights into the underlying complex dynamics. But the main goal the identification of an impending epileptic seizure with a sufficient specificity and reliability, has not been achieved up to now.
An algorithm for a reliable, automated prediction of epileptic seizures would enable the realization of implantable seizure warning devices, which could provide valuable information to the patient and time/event specific drug delivery or possibly a direct electrical nerve stimulation. Cellular Nonlinear Networks (CNN) are promising candidates for future seizure warning devices. CNN are characterized by local couplings of comparatively simple dynamical systems. With this property these networks are well suited to be realized as highly parallel, analog computer chips. Today available CNN hardware realizations exhibit a processing speed in the range of TeraOps combined with low power consumption.
In this contribution new algorithms based on the spatio-temporal dynamics of CNN are considered in order to analyze intracranial EEG signals and thus taking into account mutual dependencies between neighboring regions of the brain. In an identification procedure Reaction-Diffusion CNN (RD-CNN) are determined for short segments of brain electrical activity, by means of a supervised parameter optimization. RD-CNN are deduced from Reaction-Diffusion Systems, which usually are applied to investigate complex phenomena like nonlinear wave propagation or pattern formation. The Local Activity Theory provides a necessary condition for emergent behavior in RD-CNN. In comparison linear spatio-temporal autoregressive filter models are considered, for a prediction of EEG signal values. Thus Signal features values for successive, short, quasi stationary segments of brain electrical activity can be obtained, with the objective of detecting distinct changes prior to impending epileptic seizures.
Furthermore long term recordings gained during presurgical diagnostics in temporal lobe epilepsy are analyzed and the predictive performance of the extracted features is evaluated statistically. Therefore a Receiver Operating Characteristic analysis is considered, assessing the distinguishability between distributions of supposed preictal and interictal periods.
In previous publications,1-6 several approaches targeting the problem of seizure prediction7 in epilepsy8 have been
proposed. In this contribution recent results based on an EEG-signal prediction algorithm will be presented and
discussed in detail. Therefore segmented data aquired by multi-electrode Stereoelectroencephalography (SEEG)
and Electrocorticography (ECoG) are presented to a delay-type DTCNN with linear weight functions and a 3×1
network topology. This leads to series of signal predictors and according to that to series of prediction errors.
These prediction error series are arranged in a 2 dimensional representation called error profile.9 This profile
enables the choice of optimal positions for implanting long time electrodes, by means of which perhaps a mostly
effective seizure prediction may become possible. So far data of different patients have been studied in detail
and some distinct electrode points were found showing distinct changes before a seizure onset.
In this contribution new results in the field of video processing regarding the problem of obstacle detection will be presented.
Video sequences obtained from a camera mounted in a driving car are used as the input to a CNN and different templates are applied to extract multiple features from video sequences. Thereby, CNN with nonlinear weight functions have been considered allowing a reliable feature extraction. A detailed discussion of the algorithms and obtained results will be given in this paper.
For many epilepsy patients seizures cannot sufficiently be controlled by an antiepileptic pharmacatherapy. Furthermore, only in small number of cases a surgical treatment may be possible. The aim of this work is to contribute to the realization of an implantable seizure warning device. By using recordings of electroenzephalographical(EEG) signals obtained from the department of epileptology of the University of Bonn we studied a recently proposed algorithm for the detection of parameter changes in nonlinear systems. Firstly, after calculating the crosscorrelation function between the signals of two electrodes near the epileptic focus, a wavelet-analysis follows using a sliding window with the so called Mexican-Hat wavelet. Then the Shannon-Entropy of the wavelet-transformed data has been determined providing the information content on a time scale in subject to the dilation of the wavelet-transformation. It shows distinct changes at the seizure onset for all dilations and for all patients.
In previous publications it has been shown that the prediction algorithm for multi-layer delay-type DTCNN may be used for the analysis of EEG-signals in order to find precursors of impending epileptic seizures. It has been stated that the application of time efficient training algorithms together with the consideration of symmetric templates lead to a significant decrease of the calculation complexity, allowing the analysis of long-term recordings of EEG-signals. In this contribution EEG-data, covering a total time of 6 days, were studied, applying the BFGS (Broiden-Fletcher-Goldfarb-Shanno) training method. To accomplish a very effective procedure, several symmetries have been tested and template structures leading to higher processing speed and optimal results have been implemented for the long-term studies. Distinct changes occuring before the onsets of impending seizures in the used data set were observed for different prediction parameters.
Reaction-Diffusion systems can be applied to describe a broad class of nonlinear phenomena, in particular in biological systems and in the propagation of nonlinear waves in excitable media. Especially, pattern formation and chaotic behavior are observed in Reaction-Diffusion systems and can be analyzed. Due to their structure multi-layer Cellular Neural Networks (CNN) are capable of representing Reaction-Diffusion systems effectively. In this contribution Reaction-Diffusion CNN are considered for modeling dynamics of brain activity in epilepsy. Thereby the parameters of Reaction-Diffusion systems are determined in a supervised optimization process, and brain electrical activity using invasive multi-electrode EEG recordings is analyzed with the aim to detect of precursors of impending epileptic seizures. A detailed discussion of first results and potentiality of the proposed approach will be given.
In this paper we present our work analysing electroencephalographic (EEG) signals for the detection of seizure precursors in epilepsy. Volterra-systems and Cellular Nonlinear Networks are considered for a multidimensional signal analysis which is called the feature extraction problem throughout this contribution. Recent results obtained by applying a pattern detection algorithm and a nonlinear prediction of brain electrical activity will be discussed in detail. The aim of this interdisciplinary project is the realization of an implantable seizure warning and preventing system.
Recently CNN with nonlinear weight functions are used for various problems. Thereby nonlinear weights are represented by polynomials or tabulated functions combined with a cubic spline interpolation.
In this paper a linear interpolation technique is considered to allow an accurate approximation of nonlinear weight functions in CNN. In a previous publication the Table Minimising Algorithm (TMA) was introduced and applied to the Korteweg-de Vries-equation (KdV). In this contribution new results obtained by applying the algorithm to additional partial differential equations (PDE) will be given and discussed.
Cellular Neural Network-Universal Machines (CNN-UM) are analog devices, which are excellently suited for image processing. A big challenge thereby is the determination of CNN templates for special image processing tasks. In many cases appropriate templates can only be found by a parameter optimization. The determination of templates for complex applications in the area of CNN is usually performed by using a CNN software simulator. Unfortunately, in many cases the determined templates cannot be used in hardware realizations of CNN caused by realization effects. In order to find robust templates, which are not only working on CNN simulators, but also on hardware implementations, we present in this contribution a new kind of on-chip-multi-template-training. Furthermore, as a possible application, we will also present a CNN-based solution of the problem of Pattern Matching, which is a processing step in many areas of image processing, like e.g. in Motion Estimation, Image- and Video-Compression.
0.5% of the world population is suffering from a focal epilepsy. Several actual investigations showed that methods in nonlinear signal processing are important for the derivation of new feature extraction methods to enable the realisation of a portable epilepsy warning system. In this contribution we will present recent results for the pattern detection algorithm which we have proposed in previous investigations. In order to verify our first results we will present results of long time measurements. Furthermore the pattern detection algorithm has been transformed in order to run on the first realization of a possible warning device, which had been presented by Laiho et. al. A detail discussion of the results will be given in the paper.
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