Using static and dynamic canonical correlation coefficients as quantitative EEG markers for Alzheimer's disease severity.

We analyzed the relation between Alzheimer's disease (AD) severity as measured by Mini-Mental State Examination (MMSE) scores and quantitative electroencephalographic (qEEG) markers that were derived from canonical correlation analysis. This allowed an investigation of EEG synchrony between groups of EEG channels. In this study, we applied the data from 79 participants in the multi-centric cohort study PRODEM-Austria with probable AD. Following a homogeneous protocol, the EEG was recorded both in resting state and during a cognitive task. A quadratic regression model was used to describe the relation between MMSE and the qEEG synchrony markers. This relation was most significant in the δ and θ frequency bands in resting state, and between left-hemispheric central, temporal and parietal channel groups during the cognitive task. Here, the MMSE explained up to 40% of the qEEG marker's variation. QEEG markers showed an ambiguous trend, i.e. an increase of EEG synchrony in the initial stage of AD (MMSE>20) and a decrease in later stages. This effect could be caused by compensatory brain mechanisms. We conclude that the proposed qEEG markers are closely related to AD severity. Despite the ambiguous trend and the resulting diagnostic ambiguity, the qEEG markers could provide aid in the diagnostics of early-stage AD.

A novel method for the identification of synchronization effects in multichannel ECoG with an application to epilepsy.

In this paper, we present a novel method for the identification of synchronization effects in multichannel electrocorticograms (ECoG). Based on autoregressive modeling, we define a dependency measure termed extrinsic-to-intrinsic power ratio (EIPR) which quantifies directed coupling effects in the time domain. Hereby, a dynamic input channel selection algorithm assures the estimation of the model parameters despite the strong spatial correlation among the high number of involved ECoG channels. We compare EIPR to the partial directed coherence, show its ability to indicate Granger causality and successfully validate a signal model. Applying EIPR to ictal ECoG data of patients suffering from temporal lobe epilepsy allows us to identify the electrodes of the seizure onset zone. The results obtained by the proposed method are in good accordance with the clinical findings.

Identification of material flow systems: Extensions and case study.

The paper consists of two main parts. The first part is concerned with different aspects of mathematical modeling of material flow systems for the linear static case. The problems considered are the description of the model class, data reconciliation, identification of subsystems and the analysis of system properties relevant e.g. for simulation. In the second part an application of the modeling tools proposed in the first part to a study on the metabolism of phosphorus in an Austrian region is given.

Identification of material flow systems.

Material Flow Analysis (MFA) has become an important instrument in environmental science and pollution research. In this paper, we look at the MFA problem as a particularly structured system identification problem. Special emphasis is given to the linear, static case, where we describe a procedure for reconciliating the flow measurements and for estimating the unmeasured flows and the transfer coefficients by taking into account a priori restrictions such as balance equations.

[Dynamics of endogenous bacterial nitrite formation in the stomach. 6. Redox potential and nitrite formation in stomach secretions]. / Dynamik der endogenen bakteriellen Nitritbildung im Magen. 6. Mitteilung: Redoxpotential und Nitritbildung im Magensekret.

The redox potential depending on the pH-value and the concentration of nitrite was examined in the fasting gastric juice samples of 132 anamnestically healthy, young, voluntary test-persons. It turned out that small pH-values (acid) are associated with high redox potentials and big pH-values (neutral) with smaller redox potentials. Therefore the hydrogen ion pressure (rH-value) resulting from these two quantities generally is situated in the indifferent range. Reducing properties of the whole juice can only occasionally be found, and apparently only then, if a neutral juice is acidified. Oxidizing properties have to be classified as exceptional cases. It cannot absolutely be traced on behalf of the findings, that can be raised with natural juices, if and when answered affirmatively, which effects the redox potential has on the formation of bacterial nitrite.

Segmentation of the EEG by minimization of the total gain in information.

A new procedure for detecting departures from constancy of the parameters of a probabilistic model over a period of time is proposed. It basically consists of specification of a joint probability distribution for data and models and minimization of the total gain in information. In contrast to conventional techniques, this procedure can be used to determine both the number of different models and the positions of the points at which the switches from one model to another occur. It is demonstrated how this new method can be applied to the problem of identification of different stages of EEG background activity. The lengths of these stages might serve as indicators for drug effects in the EEG.

Procedure for identification of different stages of EEG background activity and its application to the detection of drug effects.

A procedure for the detection of a change in EEG background activity is introduced. Here the time path of the relative power in the alpha band is modelled by fitting two lines, each corresponding to a different level of background activity. The jumping point between these two lines is estimated and serves as an indicator of drug effects.