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Application of clustering techniques for visually evoked potentials based detection of vision impairments

Vijean V., M H., Yaacob S., Sulaiman M. N. B.

Biocybernetics and Biomedical Engineering

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2014

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Vol. 34, no. 3

169--177

EN

Visually evoked potentials (VEP) are evoked responses of the brain corresponding to a specific visual stimulus. Ophthalmologists often refer their patients to VEP test if the latter suffers any vision abnormalities that cannot be diagnosed using conventional analysis. By investigating the VEP responses, medical experts can narrow down the possible cause of the defect. Although this method provides valuable information to the medical practitioner, there are several drawbacks of the analysis that can affect the diagnosis result. The conventional averaging of the signals results in inter-trial variation between the VEP responses to be lost. This method also requires large number of trials, which causes fatigue in patients and reduces the diagnostic accuracy. Therefore, we have proposed a new method of analysis using statistical features derived from time and spectral space for the discrimination of vision impairments. Feature enhancement methods such as feature weighting and dimensional reduction are used to enhance the statistical features prior to the analysis. Four clustering methods are employed to increase the interclass separability of the control and myopic features while reducing the within class variability. The dimension of the weighted features is reduced using a combination of principal component analysis (PCA) and independent component analysis (ICA) techniques prior to classification. The proposed method is able to achieve 100% accuracy using extreme learning machine (ELM) and multi layer neural network (MLNN) classifiers.

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Transcranial magnetic stimulation as a tool for brain cortex excitability analysis in migraine pathophysiology

Nikitin S. S., Kurenkov A. L., Artemenko A. R.

Biocybernetics and Biomedical Engineering

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2011

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Vol. 31, no. 3

3-17

EN

Evidence is growing that neuronal excitability and responsiveness to sensory stimulation increase in migraine at cortical and brain stem levels. The perception of phosphenes induced by transcranial magnetic stimulation (TMS) allows analysis of visual cortex excitability during migraine attacks and interictal periods; TMS can also help assess prophylactic drug effects. The paper reviews studies of anticonvulsants and discuss the reduction of migraine frequency correlated inversely with an increase of phosphene thresholds and not correlated with motor thresholds. Multidisciplinary analysis along with TMS will aid our understanding of migraine mechanisms since most modem anticonvulsants have complex effects, not simply inhibition of cortical excitability.

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Quantification of motoneurone pool responses to transcranial magnetic stimulation with surface electromygraphy

Awiszus F.

Biocybernetics and Biomedical Engineering

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2005

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Vol. 25, no. 3

3-10

EN

Transcranial magnetic stimulation (TMS) is a noninvasive technique to investigate human motoneurone pools (spinal and cortical). Despite the fact that the number of publications dealing with TMS is growing rapidly, there is currently no clear standard how TMS responses should be quantified. Many current studies cite the guidelines that were published in 1994. These guidelines, however, mention (more or less implicitly) at least three ways to quantify the motor evoked potential (MEP) amplitude for a given stimulus strength. In order to clarify to what an extent these different quantification concepts provide different results, MEP measurements were performed on 12 hand muscles of 4 normal volunteers. The input/output curve derived from the threshold concept of the guidelines was found to differ significantly from the most popular concepts of input/ output curve quantification (averaged MEP amplitudes or amplitudes of averaged MEPs). On the other hand, using the median of MEP amplitudes provided an output measure that was consistent with the input/output curve derived from the threshold concept. These results indicate, that the differences in the output quantification concepts need to be taken into account when interpreting results of MEP measurements. In particular, using consistent concepts like threshold and median MEP amplitude should alleviate the problem of interpreting changes observed in MEP parameters obtained by TMS.