| 1. |
- Löfhede, Johan, et al.
(författare)
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Classification of burst and suppression in the neonatal electroencephalogram
- 2008
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Ingår i: Journal of Neural Engineering. - : Institute of Physics Publishing Ltd.. - 1741-2560 .- 1741-2552. ; 5:4, s. 402-410
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Tidskriftsartikel (refereegranskat)abstract
- Fisher's linear discriminant (FLD), a feed-forward artificial neural network (ANN) and a support vector machine (SVM) were compared with respect to their ability to distinguish bursts from suppressions in electroencephalograms (EEG) displaying a burst-suppression pattern. Five features extracted from the EEG were used as inputs. The study was based on EEG signals from six full-term infants who had suffered from perinatal asphyxia, and the methods have been trained with reference data classified by an experienced electroencephalographer. The results are summarized as the area under the curve (AUC), derived from receiver operating characteristic (ROC) curves for the three methods. Based on this, the SVM performs slightly better than the others. Testing the three methods with combinations of increasing numbers of the five features shows that the SVM handles the increasing amount of information better than the other methods.
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| 2. |
- Liljekvist Soltic, Ingela, et al.
(författare)
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Studies of host-graft interactions in vitro.
- 2007
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Ingår i: Journal of Neural Engineering. - : IOP Publishing. - 1741-2560 .- 1741-2552. ; 4:3, s. 255-263
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Tidskriftsartikel (refereegranskat)abstract
- Progenitor and stem cell transplantation represent therapeutic strategies for retinal disorders that are accompanied by photoreceptor degeneration. The transplanted cells may either replace degenerating photoreceptors or secrete beneficial factors that halt the processes of photoreceptor degeneration. The present study analyzes whether rat retinal progenitor cells differentiated into photoreceptor phenotypic cells in neurospheres have a potential to interact with rat retinal explants. Immunocytochemistry for rhodopsin and synaptophysin indicated photoreceptor cell-like differentiation in neurospheres that were stimulated by basic fibroblast growth factor and epidermal growth factor. Differentiation into neural phenotypes including photoreceptor cells was effectively blocked by an addition of leukemia inhibitory factor. Grafting of neurospheres onto retinal explants demonstrated a consistent penetration of glial cell processes into the explanted tissue. On the other hand, the incorporation of donor cells into explants was very low. A general finding was that neurospheres grafting was associated with local decrease in Muller cell activation in the explants. Further characterization of these effect(s) could provide further insight into progenitor cell-based therapies of retinal degenerative disorders.
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| 3. |
- Johansson, Johannes D., 1977-, et al.
(författare)
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Impact of cysts during radio frequency (RF) lesioning in deep brain structures : a simulation and in-vitro study
- 2007
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Ingår i: Journal of Neural Engineering. - : Institute of Physics Publishing (IOPP). - 1741-2560 .- 1741-2552. ; 4:2, s. 87-95
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Tidskriftsartikel (refereegranskat)abstract
- Radiofrequency lesioning of nuclei in the thalamus or the basal ganglia can be used to reduce symptoms caused by e.g. movement disorders such as Parkinson's disease. Enlarged cavities containing cerebrospinal fluid (CSF) are commonly present in the basal ganglia and tend to increase in size and number with age. Since the cavities have different electrical and thermal properties compared with brain tissue, it is likely that they can affect the lesioning process and thereby the treatment outcome. Computer simulations using the finite element method and in vitro experiments have been used to investigate the impact of cysts on lesions' size and shape. Simulations of the electric current and temperature distributions as well as convective movements have been conducted for various sizes, shapes and locations of the cysts as well as different target temperatures. Circulation of the CSF caused by the heating was found to spread heat effectively and the higher electric conductivity of the CSF increased heating of the cyst. These two effects were together able to greatly alter the resulting lesion size and shape when the cyst was in contact with the electrode tip. Similar results were obtained for the experiments.
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| 4. |
- Antonsson, Johan, et al.
(författare)
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Diffuse reflectance spectroscopy measurements for tissue type discrimination during deep brain stimulation
- 2008
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Ingår i: Journal of neural engineering. - : IOP Publishing. - 1741-2560 .- 1741-2552. ; 5:2, s. 185-190
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Tidskriftsartikel (refereegranskat)abstract
- Diffuse reflectance spectroscopy as a method for improving intracerebral guidance during functional neurosurgery has been investigated. An optical probe was developed for measurements during stereotactic and functional neurosurgery in man. The aim of the study was to investigate the spectral differences between white and grey matter and between white matter and functional targets. Diffuse reflectance spectroscopy measurements in ten patients were recorded at incremental steps towards and in three different functional targets (STN, GPi and Zi). The recorded spectra along the trajectory were sorted into white or grey matter, based on preoperative MRI images or the recorded spectral shape and intensity. The difference between tissue types was calculated as a quotient. Significant intensity differences between white and grey matter were found to be at least 14% (p < 0.05) and 20% (p < 0.0001) for MRI and spectral-sorted data respectively. The reflectance difference between white matter and the functional targets of GPi was higher than for STN and Zi. The results indicate that diffuse reflectance spectroscopy has a potential to be developed to a suitable complement to other intracerebral guidance methods.
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| 5. |
- Löfgren, Nils, 1969, et al.
(författare)
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Spectral distance for ARMA models applied to electroencephalogram for early detection of hypoxia
- 2006
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Ingår i: Journal of Neural Engineering. - : IOP Publishing. - 1741-2560 .- 1741-2552. ; 3:3, s. 227-34
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Tidskriftsartikel (refereegranskat)abstract
- A novel measure of spectral distance is presented, which is inspired by the prediction residual parameter presented by Itakura in 1975, but derived from frequency domain data and extended to include autoregressive moving average (ARMA) models. This new algorithm is applied to electroencephalogram (EEG) data from newborn piglets exposed to hypoxia for the purpose of early detection of hypoxia. The performance is evaluated using parameters relevant for potential clinical use, and is found to outperform the Itakura distance, which has proved to be useful for this application. Additionally, we compare the performance with various algorithms previously used for the detection of hypoxia from EEG. Our results based on EEG from newborn piglets show that some detector statistics divert significantly from a reference period less than 2 min after the start of general hypoxia. Among these successful detectors, the proposed spectral distance is the only spectral-based parameter. It therefore appears that spectral changes due to hypoxia are best described by use of an ARMA- model-based spectral estimate, but the drawback of the presented method is high computational effort.
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| 6. |
- Song, Dan, et al.
(författare)
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Computationally Efficient Models of Neuromuscular Recruitment and Mechanics
- 2008
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Ingår i: Journal of Neural Engineering. - : IOP Publishing. - 1741-2560 .- 1741-2552. ; 5:2, s. 175-184
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Tidskriftsartikel (refereegranskat)abstract
- We have improved the stability and computational efficiency of a physiologically realistic, virtual muscle (VM 3.*) model (Cheng et al 2000 J. Neurosci. Methods 101 117-30) by a simpler structure of lumped fiber types and a novel recruitment algorithm. In the new version (VM 4.0), the mathematical equations are reformulated into state-space representation and structured into a CMEX S-function in SIMULINK. A continuous recruitment scheme approximates the discrete recruitment of slow and fast motor units under physiological conditions. This makes it possible to predict force output during smooth recruitment and derecruitment without having to simulate explicitly a large number of independently recruited units. We removed the intermediate state variable, effective length (L-eff), which had been introduced to model the delayed length dependency of the activation-frequency relationship, but which had little effect and could introduce instability under physiological conditions of use. Both of these changes greatly reduce the number of state variables with little loss of accuracy compared to the original VM. The performance of VM 4.0 was validated by comparison with VM 3.1.5 for both single-muscle force production and a multi-joint task. The improved VM 4.0 model is more suitable for the analysis of neural control of movements and for design of prosthetic systems to restore lost or impaired motor functions. VM 4.0 is available via the internet and includes options to use the original VM model, which remains useful for detailed simulations of single motor unit behavior.
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